Foot/toe Pain
Foot or toe pain is discomfort arising from musculoskeletal, neurological, vascular, or dermatological conditions affecting the structures of the foot and toes, commonly caused by plantar fasciitis, metatarsalgia, gout, Morton's neuroma, or trauma.
Foot and Toe Pain
Foot and toe pain is an extraordinarily common presenting complaint encompassing any discomfort localised to the anatomical structures distal to the ankle joint — including bones, joints, tendons, ligaments, fascia, nerves, blood vessels, and skin of the foot and toes. It is not a single diagnosis but rather a clinical syndrome that demands a systematic approach to identify the underlying aetiology, which can range from the trivially mechanical (a poorly fitting shoe) to the limb-threatening (critical limb ischaemia) or even life-threatening (septic arthritis, necrotising fasciitis).
The clinical approach is best framed around anatomical location (forefoot, midfoot, hindfoot, plantar, dorsal, specific toes), temporal pattern (acute vs. chronic), mechanism (traumatic vs. atraumatic), and patient context (age, comorbidities such as diabetes mellitus or peripheral arterial disease, occupation, footwear, activity level).
Think of foot pain as a "localisation exercise." Once you know where the pain is, you can dramatically narrow your differential. A podiatrist's mantra: "Location, location, location."
- Foot pain affects approximately 17–24% of the adult population at any given time [1][2].
- Prevalence increases with age: up to 36% in those > 65 years.
- In Hong Kong specifically:
- High prevalence of gout (the most common crystal arthropathy) due to dietary habits (purine-rich seafood, shellfish, organ meats) and rising metabolic syndrome prevalence [3].
- Diabetic foot is a major burden — Hong Kong has ~700,000 people with diabetes (~10% of the population), and 25% lifetime risk of developing a foot ulcer [4].
- Peripheral arterial disease (PAD) is increasingly prevalent with an ageing population and high smoking rates among older males [3][5].
- Hallux valgus is extremely common in the Chinese population, particularly among women wearing narrow-toed shoes.
3. Anatomy and Function
Understanding foot pain demands solid knowledge of the foot's anatomy. Let me walk you through it systematically.
The foot has 26 bones (plus 2 sesamoids) organised into three functional segments:
| Segment | Bones | Key Function |
|---|---|---|
| Hindfoot | Calcaneus, Talus | Weight-bearing transmission from tibia → ground; shock absorption |
| Midfoot | Navicular, Cuboid, 3 Cuneiforms (medial, intermediate, lateral) | Structural bridge; forms the rigid "keystone" of the arches |
| Forefoot | 5 Metatarsals, 14 Phalanges (2 for hallux, 3 for each lesser toe), 2 Sesamoids (under 1st MT head) | Push-off during gait; fine balance adjustments |
Arches of the foot — these are critical for load distribution and shock absorption:
- Medial longitudinal arch (MLA): calcaneus → talus → navicular → medial cuneiform → 1st metatarsal. Highest point at the navicular. Supported by the plantar fascia (static) and tibialis posterior tendon (dynamic). Collapse = pes planus (flat foot).
- Lateral longitudinal arch: calcaneus → cuboid → 4th & 5th metatarsals. Flatter, more rigid.
- Transverse arch: across the cuneiforms and metatarsal bases.
| Joint | Type | Clinical Relevance |
|---|---|---|
| Ankle (talocrural) | Hinge (synovial) | Dorsiflexion/plantarflexion |
| Subtalar | Synovial (talus on calcaneus) | Inversion/eversion; critical in pes planus |
| Talonavicular + calcaneocuboid = Chopart's joint | Transverse tarsal | Midfoot mobility |
| Tarsometatarsal (TMT) = Lisfranc joint | Synovial | Lisfranc injury; stabilised by Lisfranc ligament (medial cuneiform to 2nd MT base) |
| Metatarsophalangeal (MTP) | Condyloid | Hallux valgus (1st MTPJ), gout, sesamoiditis |
| Interphalangeal (IP) | Hinge | Hammer toe, claw toe, mallet toe |
- Plantar fascia (plantar aponeurosis): thick fibrous band from calcaneal tuberosity to proximal phalanges. Functions as a "windlass mechanism" — when toes dorsiflex (especially the great toe), the plantar fascia tightens and elevates the MLA, converting the foot into a rigid lever for push-off [6].
- Achilles tendon: the strongest tendon in the body; composed of gastrocnemius + soleus + plantaris inserting into the calcaneus. Vulnerable zone: 2–6 cm above insertion (watershed area of relatively poor blood supply).
- Tibialis posterior tendon: primary dynamic stabiliser of the MLA. Dysfunction → progressive pes planus [6].
- Peroneal tendons (peroneus longus and brevis): evert the foot, stabilise the lateral ankle.
- Flexor hallucis longus (FHL): runs behind the medial malleolus, through a groove in the talus — prone to tenosynovitis, especially in dancers (posterior ankle impingement).
- Plantar plate: fibrocartilaginous structure on the plantar aspect of the MTPJs that resists hyperextension. Disruption → metatarsalgia, crossover toe deformity.
Arterial supply:
- Posterior tibial artery → passes behind the medial malleolus → bifurcates into medial and lateral plantar arteries (supplies the sole). The lateral plantar artery forms the plantar arch [5].
- Anterior tibial artery → continues as the dorsalis pedis artery on the dorsum of the foot (palpable between extensor hallucis longus and extensor digitorum longus tendons).
- Peroneal (fibular) artery → gives branches to the lateral ankle and heel.
Nerve supply:
- Tibial nerve → passes through the tarsal tunnel (behind medial malleolus, under flexor retinaculum) → divides into medial and lateral plantar nerves. Compression here = tarsal tunnel syndrome.
- Deep peroneal nerve → innervates dorsum of 1st web space and extensor digitorum brevis.
- Superficial peroneal nerve → sensory to dorsum of foot.
- Sural nerve → lateral border of foot.
- Common digital nerves (from lateral and medial plantar nerves) → pass between metatarsal heads. Compression/neuroma formation between the metatarsal heads = Morton's neuroma (most commonly between 3rd and 4th metatarsal heads).
- Medial plantar nerve, 1st branch of lateral plantar nerve (Baxter's nerve) → innervates abductor digiti minimi; entrapment → chronic medial heel pain (often confused with plantar fasciitis).
Clinical Pearl
When examining the foot, always palpate both the dorsalis pedis and posterior tibial pulses. Absence of both suggests significant peripheral arterial disease. In diabetic patients, the ABPI may be falsely elevated due to medial arterial calcification (Mönckeberg sclerosis), so a toe-brachial index (TBI) or transcutaneous oxygen pressure (TcPO₂) is more reliable [4][5].
The foot has 9 compartments (medial, lateral, central superficial, central deep [calcaneal], 4 interossei compartments, and adductor). This is clinically relevant because crush injuries or severe fractures can cause foot compartment syndrome — missed diagnosis leads to contracture, chronic pain, and potential amputation.
I'll organise aetiologies by anatomical region and then by the major pathophysiological categories. For each, I'll explain the "why" — the mechanism that leads to pain.
4.1 By Pathophysiological Category
4.1.1 Mechanical / Degenerative
| Condition | Pathophysiology | HK Relevance |
|---|---|---|
| Plantar fasciitis | Repetitive microtrauma → microtears at calcaneal origin of plantar fascia → chronic inflammatory and degenerative changes (actually more "fasciosis" than "fasciitis" histologically, as inflammatory cells are sparse — it is a degenerative process with failed healing) [6] | Very common in HK: prolonged standing (service industry), running on hard surfaces, obesity epidemic |
| Hallux valgus ("bunion") | Lateral deviation of the great toe at the 1st MTPJ + medial deviation of the 1st metatarsal. Intrinsic muscle imbalance (adductor hallucis overpowers abductor hallucis) → progressive deformity → bunion pain (friction over medial eminence), 1st MTPJ arthritis, transfer metatarsalgia (2nd/3rd MTPJs overloaded) [6] | Extremely common in Chinese women; narrow footwear, high heels; family history strong |
| Hallux rigidus | OA of the 1st MTPJ → loss of dorsiflexion → painful stiff great toe, especially during push-off phase of gait | Increases with age |
| Metatarsalgia | Overload of lesser metatarsal heads (often from transfer due to hallux valgus, Morton's neuroma, or plantar plate insufficiency) → pain under MT heads on weight-bearing | |
| Pes planus (flat foot) | Collapse of MLA, most commonly from tibialis posterior tendon dysfunction (TPTD) — the tendon degenerates → cannot support the arch → progressive valgus hindfoot + forefoot abduction [6] | Common; associated with obesity, middle-aged women |
| Pes cavus (high-arched foot) | Often neuromuscular in origin (e.g., Charcot-Marie-Tooth disease — weakening of tibialis anterior and peroneus brevis → unopposed plantarflexion of 1st ray + hindfoot varus). Leads to overload of MT heads → callosities, claw toes, lateral ankle instability [6] | Always think neurological cause — examine for CMT, muscular dystrophy |
| Hammer/claw/mallet toe | Imbalance of intrinsic vs. extrinsic toe muscles → fixed flexion deformities at PIP (hammer), DIP (mallet), or both (claw) → pain from shoe friction over dorsal prominences + metatarsalgia | Common with hallux valgus, pes cavus, RA, DM neuropathy |
4.1.2 Traumatic
| Condition | Mechanism |
|---|---|
| Metatarsal fracture | Direct trauma or stress fracture (2nd/3rd MT most common stress fracture site — "march fracture" in military recruits). The 5th MT base avulsion fracture ("dancer's fracture") occurs with ankle inversion (peroneus brevis avulses the base). Differentiate from Jones fracture (5th MT metaphyseal-diaphyseal junction) — prone to non-union due to watershed blood supply |
| Lisfranc injury | Disruption of the TMT joint complex. Can be subtle on X-ray. Mechanism: axial load on a plantarflexed foot (e.g., car pedal injury, misstep). Hallmark: diastasis between 1st and 2nd MT bases on weight-bearing XR. Missed diagnosis → chronic pain, arthritis [6] |
| Turf toe | Hyperextension sprain of the 1st MTPJ → plantar plate injury. Common in athletes on artificial turf |
| Calcaneal fracture | High-energy axial load (fall from height). Often bilateral. Associated with lumbar spine burst fracture (10%) — always examine the spine! Böhler's angle (normally 25–40°) is flattened |
| Toe fractures | Stubbing injuries; usually managed conservatively with buddy taping unless great toe or significantly displaced/rotated |
4.1.3 Inflammatory / Crystal Arthropathy
| Condition | Pathophysiology | HK Relevance |
|---|---|---|
| Gout | Hyperuricaemia → monosodium urate (MSU) crystal deposition in joints (preferentially 1st MTPJ — "podagra" = "foot trap" from Greek). Why the 1st MTPJ? — it is the coolest peripheral joint, lowest pH locally, and subject to microtrauma, all favouring crystal nucleation. Crystals trigger NLRP3 inflammasome → IL-1β release → intense neutrophilic inflammation → exquisitely painful, red, hot, swollen joint [3] | Very high prevalence in HK — dietary purine intake (seafood, organ meats, beer), metabolic syndrome, diuretic use in elderly; prevalence ~2.9% in men [3] |
| Calcium pyrophosphate deposition (CPPD) / pseudogout | CPP crystal deposition in cartilage → acute inflammatory arthritis. Less commonly affects the foot (knee is classical), but can involve midfoot, 1st MTPJ | ↑ with age [3] |
| Rheumatoid arthritis | Autoimmune synovitis → pannus formation → erosion of MTPJ cartilage/bone. Characteristically affects MTPJs symmetrically → forefoot pain, hallux valgus, claw toes, subluxation of MT heads through plantar skin ("walking on pebbles") | |
| Psoriatic arthritis | Enthesitis (inflammation at tendon/ligament insertions) + dactylitis ("sausage digit") + distal IP joint arthritis. Achilles enthesitis and plantar fasciitis common | |
| Reactive arthritis / seronegative spondyloarthropathy | Post-infectious immune-mediated arthritis, often affecting lower limb joints including ankle and foot; enthesitis at Achilles insertion or plantar fascia origin |
4.1.4 Infectious
| Condition | Pathophysiology |
|---|---|
| Septic arthritis | Haematogenous spread or direct inoculation → bacteria in joint space → neutrophilic inflammation → rapid cartilage destruction. In foot: 1st MTPJ, midfoot joints. Must be differentiated from gout (joint aspiration is essential) |
| Osteomyelitis | Direct spread from diabetic foot ulcer or haematogenous seeding → infection of bone. In the foot, often involves MT heads or calcaneus in diabetic patients. Probe-to-bone test has high specificity (~89%) for osteomyelitis in diabetic foot ulcers [4] |
| Cellulitis / erysipelas | Bacterial infection of skin and subcutaneous tissue; foot is common site especially with tinea pedis (provides portal of entry), venous insufficiency, or lymphoedema |
| Pitted keratolysis | Superficial infection with Corynebacterium spp → multiple asymptomatic circular 'punched-out' pits, usually bilaterally at pressure-bearing areas of foot [3] |
4.1.5 Vascular
This is a high-yield category for exams.
A. Arterial
Chronic limb ischaemia (CLI) [5]:
-
Cause: Atherosclerosis is the most common cause of chronic arterial insufficiency [5].
-
Risk factors: Current or previous smoking (strongest RF, 3–6× risk for intermittent claudication), DM (2× ↑ risk, 26% ↑ risk of PAD for every 1% ↑ HbA₁c), hyperlipidaemia, pre-existing arterial disease (CAD, stroke/TIA, carotid disease), family history of vascular disease [5].
-
Pathophysiology: Progressive atherosclerotic narrowing of arteries → reduced perfusion. Initially compensated by collateral development. When demand exceeds supply during exercise → intermittent claudication. When supply cannot meet even resting metabolic demand → rest pain, ulceration, gangrene (= critical limb ischaemia).
-
Fontaine classification [5]:
- Stage 1 = Asymptomatic
- Stage 2 = Intermittent claudication (2a: claudication distance > 200m; 2b: < 200m)
- Stage 3 = Ischaemic rest pain
- Stage 4 = Ulceration or gangrene
-
Intermittent claudication — "claudicare" = "to limp" [5]:
- A reproducible discomfort of a defined group of muscles, induced by exercise and relieved by rest
- "Shop window to shop window" pattern: not present at first step (cf. OA), appears after walking a fixed distance (claudication distance), and is relieved by ≤ 10 minutes of standing still
- The obstruction is one joint above the claudicating muscle [5]:
- Aortoiliac occlusion: bilateral buttock/thigh/calf claudication ± impotence (= Leriche's syndrome: triad of buttock claudication, absent/diminished femoral pulses, erectile dysfunction [5])
- Femoropopliteal occlusion: unilateral calf claudication — commonest site (70% of PAD affects the superficial femoral artery) [5]
- Tibial-peroneal occlusion: unilateral calf/foot claudication
| Vascular Claudication | Neurogenic Claudication | |
|---|---|---|
| Cause | Chronic arterial insufficiency → exercise-induced muscle ischaemia | Prolapsed IVD or OA spine → spinal stenosis → compression on spinal arteries → lumbosacral root ischaemia |
| Nature | LL discomfort on exertion | LL discomfort on exertion |
| Precipitation | Claudication distance constant | Claudication distance variable |
| Relief | "Shop window to shop window" (relief upon standing still) | "Park bench to park bench" (relief upon flexion of spine). Going downstairs > upstairs |
| Pain at rest | None | May be present (prefer to stand in slight flexion) |
| Other complaints | Nil | Paraesthesia, numbness, weakness |
-
Rest pain [5]:
- Continuous, severe unremitting pain caused by severe ischaemia
- NOT a severe form of claudication (different nature) — claudication is muscle pain from exercise; rest pain is skin/subcutaneous ischaemia when even basal metabolic need is not met
- Region: usually the least perfused area — toes and forefoot (cf. claudication felt in muscle groups)
- Severity: very severe, wakes patient from sleep, requires opioid analgesics
- ↑ with raising limb or lying flat (gravity no longer assists perfusion); ↓ by putting limb in dependent position (e.g., hanging foot over edge of bed) — this is why patients with rest pain often sleep sitting up or with the leg dangling
- If gangrene present, pain felt at junction of living and dead tissues
-
Gangrene [5]:
- Dry gangrene: hard, dry, shrunken; non-infected; clear line of demarcation between viable and necrotic tissue; safe to allow self-amputation after demarcation with precautions against infection
- Wet gangrene: soft, moist, swollen; infected; no clear line of demarcation; emergency requiring surgical debridement or amputation
Buerger's disease (thromboangiitis obliterans) [5]:
- Recurrent progressive inflammation of small/medium vessels of hands and feet
- Usually young (30–40s) males who are smokers
- Pathophysiology: unknown; histology shows acute inflammation of the wall with luminal thrombosis of small and medium arteries and veins of hands and feet
- Affects LL > UL
- Clinical features: arterial occlusive disease (rest pain, digital ulcers, gangrene), superficial thrombophlebitis, Raynaud's phenomenon
B. Venous
Chronic venous insufficiency (CVI) can cause foot pain/discomfort [5]:
- Mechanism: ambulatory venous hypertension → interstitial oedema → tissue hypoxia → skin changes → ulceration (typically around the medial malleolus/gaiter area, NOT the forefoot — this distinguishes venous from arterial ulcers)
- Venous claudication: LL discomfort that ↑ upon standing and walking, ↓ by raising leg (opposite pattern to arterial claudication) [5]
4.1.6 Neuropathic
| Condition | Pathophysiology |
|---|---|
| Morton's neuroma (interdigital neuroma) | Not a true neuroma but perineural fibrosis of the common digital nerve, most often in the 3rd intermetatarsal space (between 3rd and 4th MT heads). Compression by transverse metatarsal ligament + repetitive weight-bearing → nerve irritation → burning forefoot pain radiating to toes, relieved by removing shoes. "Morton" = Thomas Morton, who described it in 1876 |
| Tarsal tunnel syndrome | Compression of the tibial nerve in the tarsal tunnel (behind medial malleolus, under flexor retinaculum). Analogous to carpal tunnel syndrome in the wrist. Causes burning, tingling, numbness on the sole. Exacerbated by prolonged standing, dorsiflexion, eversion |
| Diabetic peripheral neuropathy | Metabolic or osmotic neurotoxicity due to chronic hyperglycaemia → polyol pathway activation (glucose → sorbitol → fructose via aldose reductase; sorbitol accumulates in Schwann cells → osmotic damage) + advanced glycation end-products (AGEs) → microvascular damage → nerve ischaemia. Symmetrical, distal, usually begins in LL → "glove-and-stocking" sensory loss + loss of protective sensation → foot ulcers, deformities, Charcot arthropathy [4] |
| Charcot arthropathy (neuropathic arthropathy) | Chronic progressive destructive arthropathy due to loss of pain or proprioception [4][6]. Lack of proprioception → ligament laxity → joint instability + deformity → prone to damage by minor trauma + vasomotor changes due to autonomic neuropathy lead to exaggerated local inflammatory response → arthropathy. Classically DM and syphilis (tabes dorsalis). Joint involved: tarsal/TMTJ > MTPJ/ankle. Clinical: painless foot/ankle deformities with warmth, redness, and oedema [4][6] |
| Baxter's nerve entrapment | Entrapment of the 1st branch of the lateral plantar nerve → chronic medial heel pain (mimics plantar fasciitis; key differentiator: tenderness more posterior and lateral than classic plantar fasciitis) |
Common Exam Pitfall
Do NOT confuse Charcot arthropathy (painless destructive joint disease from neuropathy) with cellulitis or DVT — all three can present with a warm, swollen, red foot. The key distinguishing feature: Charcot is painless (or disproportionately painless relative to the dramatic physical findings), while cellulitis is painful with systemic signs, and DVT causes calf tenderness with unilateral pitting oedema.
4.1.7 Dermatological (causes of foot/toe pain often overlooked!)
| Condition | Details |
|---|---|
| Ingrown toenail (onychocryptosis) | Lateral nail edge penetrates the nail fold → inflammation → secondary infection → granulation tissue. Most common in the great toe. Causes: improper nail trimming, tight shoes, hyperhidrosis. Very common in HK |
| Subungual exostosis | Bony outgrowth under the toenail (usually great toe) → nail lifting + pain. Diagnosed on XR |
| Plantar wart (verruca plantaris) | HPV infection of plantar skin → inwardly growing verrucous lesion at pressure points. Painful because it grows inward (pushed by body weight), compressing dermal nerve endings. Key sign: pinpoint bleeding when pared (thrombosed capillaries) — pain with lateral compression (vs. callus: pain with direct pressure) |
| Corns and calluses | Hyperkeratosis from chronic friction/pressure. Callus = diffuse thickening; corn = focal conical thickening with a central core pressing on dermis → pain |
| Erythrasma | Mild, chronic, localised superficial skin infection by Corynebacterium minutissimum. Commonest at moist areas, e.g. toe webs. Coral-red fluorescence under Wood's lamp [3] |
| Tinea pedis | Dermatophyte infection; interdigital type most common (maceration between toes, especially 4th web space). Relevant as portal of entry for cellulitis |
4.1.8 Neoplastic (rare but must not miss)
- Osteoid osteoma of metatarsals/phalanges: nocturnal pain relieved by NSAIDs; XR shows nidus with surrounding sclerosis.
- Ewing sarcoma / osteosarcoma: rare in foot but consider in young patients with progressive bony pain and swelling.
- Plantar fibromatosis (Ledderhose disease): benign fibrous nodules in the plantar fascia — analogous to Dupuytren's contracture in the hand. Usually painless but can become painful if large.
- Malignant melanoma (acral lentiginous subtype): important in Asian populations including Hong Kong Chinese — occurs on palms, soles, nail beds. A pigmented lesion on the sole or subungual melanonychia (dark streak under the nail) must be taken seriously.
High Yield for HK Exams
Acral lentiginous melanoma is the most common subtype of melanoma in Asians and darker-skinned populations. Always examine the sole and nails! Apply the ABCDE criteria and Hutchinson's sign (periungual pigmentation extending to the nail fold).
5. Classification
Foot/toe pain can be classified in several ways. A practical clinical classification:
| Must not miss | Why |
|---|---|
| Critical limb ischaemia | Limb loss if not revascularised |
| Acute arterial occlusion (6 Ps) | Irreversible muscle damage in 4–6 hours |
| Compartment syndrome (foot) | Muscle necrosis → contracture if fasciotomy delayed |
| Septic arthritis | Joint destruction within hours |
| Osteomyelitis | Progressive bone destruction, systemic sepsis |
| Necrotising fasciitis | Rapidly fatal soft tissue infection |
| Diabetic foot infection | Risk of sepsis and amputation |
| Acral lentiginous melanoma | Late diagnosis → metastasis |
| Lisfranc injury (subtle) | Missed → chronic midfoot arthritis/pain |
Already detailed above:
- Stage 1: Asymptomatic
- Stage 2: Intermittent claudication (2a: > 200m; 2b: < 200m)
- Stage 3: Ischaemic rest pain
- Stage 4: Ulceration or gangrene
Depth classification:
- Grade 0: No break in skin
- Grade 1: Superficial ulcer
- Grade 2: Exposed tendons, joints
- Grade 3: Exposed bone and/or abscess/osteomyelitis
Ischaemia classification:
- Grade A: No ischaemia
- Grade B: Ischaemia, not gangrenous
- Grade C: Partial foot gangrene
- Grade D: Complete gangrene
6. Clinical Features
6.1 Symptoms (with pathophysiological basis)
I'll organise by the major conditions that present with foot/toe pain, explaining why each symptom occurs.
| Symptom | Conditions | Pathophysiological Basis |
|---|---|---|
| Sharp forefoot pain localised to 1st MTPJ, exquisitely tender, worst at night or early morning, sudden onset | Gout (podagra) | MSU crystal deposition triggers NLRP3 inflammasome → IL-1β → intense neutrophilic inflammation. Urate solubility decreases at cooler temperatures (foot is peripherally cooled) and lower pH (tissue acidosis at rest). Nocturnal exacerbation: mild dehydration during sleep → relative hyperuricaemia; also, cortisol nadir at night reduces endogenous anti-inflammatory effect [3] |
| Burning pain in forefoot, radiating to 3rd/4th toes, worse with tight shoes, relieved by removing shoes and massaging the forefoot | Morton's neuroma | Perineural fibrosis of common digital nerve (3rd interspace) between MT heads → nerve compression during weight-bearing → neuropathic burning/shooting pain. Tight shoes compress the transverse arch further |
| Plantar heel pain, worst with first few steps in the morning (after inactivity) and toe dorsiflexion | Plantar fasciitis | During sleep/rest, the plantar fascia contracts in a slightly shortened position. First steps after rest re-stretch the damaged fascia → tearing of newly forming repair tissue → acute pain. After walking (warm-up), pain may improve as the fascia "loosens." Dorsiflexion of the great toe tightens the fascia via the windlass mechanism → pain [6] |
| Posterior heel/ankle pain, worse with activity, especially running/jumping | Achilles tendinopathy | Repetitive eccentric loading → microtears in the tendon within the watershed zone (2–6 cm above insertion) → failed healing → tendinosis. Pain is worse with activity because eccentric loading (e.g., pushing off, going downstairs) stresses the damaged fibres [6] |
| Sudden "pop" at the back of ankle during activity, followed by severe pain and inability to push off | Achilles tendon rupture | Acute failure of the previously degenerated or normal tendon under sudden eccentric load. "Pop" = audible snap of tendon. Cannot plantarflex against resistance (though weak plantarflexion may persist via tibialis posterior, peroneus longus/brevis) [6] |
| Intermittent cramping pain in calf/foot with walking, relieved by rest, reproducible at a fixed distance | Intermittent claudication (PAD) | Exercise ↑ metabolic demand in muscle → atherosclerotic narrowing limits blood flow → supply-demand mismatch → anaerobic metabolism → lactic acid accumulation → muscle pain. Rest ↓ demand → supply becomes adequate again → pain resolves [5] |
| Severe, continuous aching pain in toes/forefoot at rest, worse at night/when lying flat, relieved by dangling leg over bed | Ischaemic rest pain (critical limb ischaemia) | Basal perfusion inadequate for skin/subcutaneous tissue metabolic needs. Lying flat removes gravitational assistance to perfusion (normally ~30 mmHg boost from gravity in dependent position) → pain worsens. Dangling leg restores gravitational assist → pain improves [5] |
| Deep, boring bone pain, worse at night, relieved by NSAIDs | Osteoid osteoma | Benign bone tumour with nidus producing prostaglandins (PGE₂) → local vasodilation + nerve sensitisation → pain. NSAIDs inhibit COX → ↓PGE₂ → pain relief (pathognomonic response) |
| Pain under 2nd/3rd MT heads, worse with weight-bearing, "walking on a pebble" | Metatarsalgia / Freiberg's disease | Metatarsalgia: overload of lesser MT heads (often from 1st ray insufficiency in hallux valgus). Freiberg's disease: osteochondrosis (AVN) of the 2nd MT head in adolescents → subchondral collapse → pain |
| Midfoot pain and swelling after twisting/stepping off a curb, difficulty bearing weight | Lisfranc injury | Disruption of the strong plantar Lisfranc ligament (C1 → M2 base) + TMT joint complex → structural instability → weight-bearing transmits force through an unstable joint → pain |
| "Sausage toe" / diffuse toe swelling with pain | Dactylitis (psoriatic arthritis, reactive arthritis, sarcoidosis) | Inflammation of the entire digit (joint + tendon sheath + soft tissue) rather than just the joint → fusiform swelling of the entire toe |
| Painless foot/ankle with warmth, redness, swelling ± progressive deformity | Charcot arthropathy | Loss of proprioception → unrecognised microtrauma → progressive joint destruction; autonomic neuropathy → vasomotor dysregulation → exaggerated inflammatory response → bony resorption and collapse [4][6] |
| Symptom | Conditions | Why |
|---|---|---|
| Numbness / tingling (paraesthesia) in stocking distribution | Diabetic neuropathy, B₁₂ deficiency, alcoholic neuropathy | Damage to small sensory fibres → positive symptoms (paraesthesia = spontaneous firing of damaged nerve fibres) or negative symptoms (numbness = loss of sensory transduction) |
| Numbness specifically in the sole | Tarsal tunnel syndrome | Tibial nerve compressed in tarsal tunnel → distal sensory territory (sole) affected |
| Cold, pale foot that becomes blue then red (triphasic colour change) | Raynaud's phenomenon (seen in Buerger's disease, CTD) | Vasospasm → pallor (white) → deoxygenation (blue/cyanosis) → reactive hyperaemia (red) upon rewarming |
| Superficial thrombophlebitis | Buerger's disease | Inflammation of small/medium veins as part of the pan-vascular inflammatory process [5] |
| Skin changes: hair loss, shiny/atrophic skin, nail dystrophy | Chronic limb ischaemia | Chronic reduced perfusion → inadequate nutrition to skin appendages → atrophy of hair follicles, nail matrix, skin |
| Venous eczema, haemosiderin pigmentation, lipodermatosclerosis | Chronic venous insufficiency | Ambulatory venous hypertension → red cell extravasation → haemosiderin deposition (brown pigmentation); chronic inflammation → fibrosis (lipodermatosclerosis) [5] |
| Systemic features (fever, malaise, weight loss) | Septic arthritis, osteomyelitis, inflammatory arthritis (RA, gout), vasculitis, malignancy | Systemic inflammatory response / infection / paraneoplastic |
6.2 Signs (with pathophysiological basis)
| Sign | Conditions | Why |
|---|---|---|
| Hallux valgus angle (lateral deviation of great toe with medial prominence/bunion) | Hallux valgus | Imbalance of forces across 1st MTPJ → medial capsule stretches, lateral structures contract → progressive deviation. Measured on AP weight-bearing XR: HV angle (normal < 15°) and intermetatarsal angle (normal < 9°) [6] |
| Claw toes (MTP hyperextension + PIP & DIP flexion) | Intrinsic muscle weakness (DM neuropathy, RA, pes cavus) | Loss of intrinsic muscle function (lumbricals/interossei) → unchecked pull of long flexors and extensors → hyperextension at MTP, flexion at IP joints |
| Ulcer at forefoot/toe tip (arterial ulcer) vs. medial malleolar region (venous ulcer) | PAD vs. CVI | Arterial: ischaemia most severe distally → tissue necrosis at tips/pressure points; well-defined, "punched out," pale/necrotic base, painful. Venous: ambulatory venous HTN highest at gaiter region (medial malleolus) → shallow, irregular edges, sloughy base, relatively painless |
| Dry gangrene (black, dry, shrunken, clear demarcation) vs. wet gangrene (swollen, infected, no clear demarcation) | Critical limb ischaemia | Dry: coagulative necrosis from gradual arterial occlusion without superimposed infection. Wet: infected necrotic tissue → liquefactive necrosis → surgical emergency [5] |
| Rocker-bottom foot deformity | Charcot arthropathy | Collapse of midfoot arch → reversed arch (the bony prominences create the "rocker-bottom" shape) [4] |
| Swollen, red, hot 1st MTPJ | Acute gout | Intense neutrophilic inflammatory response to MSU crystals → vasodilation (red), increased vascular permeability (swollen), inflammatory mediators (hot, tender) |
| Tophi (white/yellowish chalky deposits under skin) | Chronic tophaceous gout | MSU crystal deposits in soft tissues, visible through skin; commonly at 1st MTPJ, Achilles tendon, olecranon bursa |
| "Too many toes" sign (viewing from behind, more lateral toes visible than normal) | Pes planus / TPTD | Forefoot abduction due to loss of tibialis posterior support → when viewed posteriorly, the forefoot splays laterally |
| Coleman block test | Pes cavus | Stand on a 1-inch wood block under lateral foot to offload the 1st MT. Corrected hindfoot varus = forefoot-driven cavus; uncorrected = both forefoot and hindfoot deformity [6] |
| Sign | Conditions | Why |
|---|---|---|
| Tenderness over plantar fascia origin (medial calcaneal tuberosity) | Plantar fasciitis | Maximal degeneration/microtearing at the calcaneal origin where tensile stress is highest [6] |
| Tenderness at Achilles tendon 2–6 cm above insertion | Achilles tendinopathy | Watershed zone of blood supply → most vulnerable to degeneration [6] |
| Mulder's click (lateral compression of MT heads while pushing up between 3rd/4th MT from plantar side → palpable/audible click + pain reproduction) | Morton's neuroma | Squeezing MT heads compresses the neuroma between them → painful click as the fibrosed nerve snaps past the transverse metatarsal ligament |
| Tinel's sign (tapping behind medial malleolus → tingling/pain radiating to sole) | Tarsal tunnel syndrome | Tapping a compressed/damaged nerve generates ectopic action potentials → shooting paraesthesia distally |
| Absent/diminished dorsalis pedis and/or posterior tibial pulses | PAD | Atherosclerotic narrowing/occlusion → reduced pulse transmission distally [5] |
| Warmth and swelling without proportionate pain | Charcot arthropathy | Neuropathy masks pain; autonomic dysfunction causes local hyperaemia → warmth |
| Squeeze test (compressing midfoot from medial/lateral → pain) | Lisfranc injury | Displaces the TMT joints → provokes pain from ligamentous disruption |
| Ankle-brachial index (ABI) < 0.9 | PAD | Lower ankle pressure relative to brachial pressure indicates arterial insufficiency proximal to the ankle. ABI ≤ 0.5 suggests critical limb ischaemia [5]. In DM, ABPI may be falsely elevated due to vessel calcification → use TcPO₂ (good wound healing potential if > 30 mmHg) or toe-brachial index instead [4][6] |
| Test | How to Perform | What It Tests | Positive Finding |
|---|---|---|---|
| Thompson (Simmonds) test | Patient prone, squeeze calf | Achilles tendon integrity | Positive if no plantar flexion of foot when calf squeezed = rupture [6] |
| Jack's test | Passive dorsiflexion of great toe | Plantar fascia/windlass mechanism | Accentuation of MLA (arch rises); failure = rigid flat foot [6] |
| Tip-toe test | Stand on tiptoes | Tibialis posterior function + flexible vs. rigid flat foot | Rigid flat foot: medial arch still not formed and hindfoot valgus still present on tiptoe [6] |
| Single-leg heel raise | Stand on one leg, raise onto tiptoes x10 | Achilles tendon + tibialis posterior | Inability to do single-leg heel raise = significant Achilles or tibialis posterior pathology [6] |
| Buerger's test | Raise legs 45° for 1–2 min → hang legs off bed | Arterial sufficiency | Positive: pallor on elevation (Buerger's angle < 20° = severe ischaemia), then reactive hyperaemia/rubor on dependency (dependent rubor) |
| Silfverskiöld test | Assess ankle dorsiflexion with knee extended vs. flexed | Gastrocnemius vs. Achilles contracture | If dorsiflexion improves with knee flexion → isolated gastrocnemius tightness (because gastrocnemius crosses the knee) |
Exam Key
A systematic foot examination should include: Look (skin, deformity, ulcers, nails, interdigital spaces), Feel (pulses, temperature, tenderness, sensation — monofilament + tuning fork), Move (active and passive ROM of ankle, subtalar, midfoot, MTPJs), Special tests (Thompson, tip-toe, Jack's, Mulder's, Tinel's, ABI), and Gait (antalgic gait, Trendelenburg, foot drop).
| Condition | Key Symptoms | Key Signs |
|---|---|---|
| Plantar fasciitis | First-step heel pain in morning | Tenderness at medial calcaneal tuberosity; ↑ pain with great toe dorsiflexion |
| Achilles tendinopathy | Posterior heel pain with activity | Tenderness 2–6 cm above insertion; thickened tendon; ↓ single-leg heel raise |
| Morton's neuroma | Burning forefoot pain → 3rd/4th toes; relieved by shoe removal | Mulder's click positive |
| Hallux valgus | Bunion pain, 1st MTPJ pain, transfer metatarsalgia | Lateral toe deviation, medial prominence, HV angle > 15° on XR |
| Gout | Excruciating 1st MTPJ pain, acute onset, nocturnal | Red, hot, swollen 1st MTPJ; tophi in chronic |
| PAD - Claudication | Calf/foot cramping on walking, fixed distance, relieved by rest | Absent pulses, hair loss, atrophic skin, ABI < 0.9 |
| PAD - Rest pain | Continuous forefoot/toe pain, ↑lying flat, ↓dangling leg | Pallor on elevation, dependent rubor, absent pulses |
| Diabetic foot | May be painless (neuropathy!) | Ulcers at pressure points, loss of sensation (monofilament), deformity, Charcot changes |
| Tarsal tunnel syndrome | Burning/tingling sole | Tinel's sign behind medial malleolus |
| Stress fracture (MT) | Gradual onset forefoot pain with activity, focal tenderness | Point tenderness over MT shaft; may be normal on initial XR (positive at 2–3 weeks) |
7. Key Concepts — Pathophysiology Deep Dive
Three factors converge at the 1st MTPJ:
- Temperature: The foot is the coolest part of the body; MSU crystal solubility decreases at lower temperatures → preferential crystal nucleation.
- pH: Local tissue pH is slightly lower in peripheral, poorly vascularised regions → further reduces urate solubility.
- Microtrauma: The 1st MTPJ bears significant load during gait → repetitive mechanical stress → crystal shedding from cartilage surface into joint space → inflammation.
When the patient lies flat, the foot loses the gravitational component of perfusion pressure. In a standing/sitting position, the column of blood from the heart to the foot adds approximately 90–100 mmHg of hydrostatic pressure at the ankle. In severe PAD where perfusion pressure is critically marginal, losing this gravitational boost tips the balance from barely adequate to inadequate → ischaemic pain. This is why patients with critical limb ischaemia instinctively hang their leg off the bed or sleep in a chair [5].
During sleep, the foot naturally adopts a plantarflexed position, allowing the plantar fascia to rest in a shortened, contracted state. The degenerative micro-tears undergo partial healing/fibrosis overnight in this shortened position. Upon standing and bearing weight, the fascia is suddenly stretched → micro-tears in the newly forming repair tissue → acute pain. After a few minutes of walking, the fascia "warms up" and becomes more pliable, and pain diminishes (but may return with prolonged standing) [6].
High Yield Summary
Definition: Foot/toe pain is a syndromic presentation requiring localisation (forefoot/midfoot/hindfoot) and categorisation (traumatic/mechanical/inflammatory/vascular/neuropathic/infectious/neoplastic) to reach a diagnosis.
Epidemiology: Affects 17–24% of adults; higher in elderly, diabetics, obese. In HK: gout, diabetic foot, hallux valgus, PAD are especially prevalent.
Anatomy: 26 bones, 3 arches (medial longitudinal most clinically important), key structures: plantar fascia (windlass mechanism), Achilles tendon (watershed zone 2–6 cm), tibialis posterior (MLA stabiliser), tarsal tunnel (tibial nerve), intermetatarsal space (Morton's neuroma).
Key aetiologies by location:
- Forefoot: Gout (1st MTPJ), hallux valgus, Morton's neuroma, metatarsalgia, stress fracture, sesamoiditis
- Midfoot: Lisfranc injury, Charcot arthropathy, tarsal coalition
- Hindfoot: Plantar fasciitis (MC cause of heel pain), Achilles tendinopathy/rupture, calcaneal fracture, tarsal tunnel syndrome, retrocalcaneal bursitis
Vascular: PAD from atherosclerosis — Fontaine stages 1–4; intermittent claudication ("shop window to shop window," obstruction one joint above); rest pain (forefoot/toes, ↑lying flat, ↓dependent, requires opioids); gangrene (dry vs. wet). Buerger's disease in young male smokers.
Neuropathic: Diabetic neuropathy → loss of protective sensation → ulcers + Charcot arthropathy (painless joint destruction). ABPI unreliable in DM (calcified vessels) → use TcPO₂ or TBI.
Key clinical features:
- Plantar fasciitis: first-step heel pain, tender medial calcaneal tuberosity
- Achilles: pain 2–6 cm above insertion, Thompson test for rupture
- Gout: acute red-hot-swollen 1st MTPJ, nocturnal, MSU crystals
- PAD: claudication distance, absent pulses, ABI < 0.9, rest pain relieved by dependency
- Morton's neuroma: Mulder's click, 3rd interspace burning pain
- Charcot: warm swollen painless foot in diabetic patient
Must not miss: Critical limb ischaemia, acute arterial occlusion, septic arthritis, osteomyelitis, necrotising fasciitis, Lisfranc injury, acral melanoma.
Active Recall - Foot/Toe Pain: Etiology, Pathophysiology, and Clinical Features
[1] Lecture slides: murtagh merge.pdf [2] Thomas MJ et al. The population prevalence of foot and ankle pain. Pain. 2011;152(12):2870–2880. [3] Senior notes: Ryan Ho Rheumatology.pdf (Section 2.4 Crystal-Induced Arthritis; Section 4.3.1.4 Other Bacterial Infections) [4] Senior notes: Ryan Ho Endocrine.pdf (p98–99, Diabetic Foot, Diabetic Neuropathy, Charcot Arthropathy) [5] Senior notes: Ryan Ho Cardiology.pdf (p205–218, Peripheral Arterial Disease, Intermittent Claudication, Rest Pain, Buerger's Disease; p233–235 Chronic Venous Insufficiency) [6] Senior notes: maxim.md (Sections 8.3–8.4, Hallux Valgus, Pes Planus, Pes Cavus, Achilles tendinopathy, Plantar fasciitis, Diabetic foot ulcers, Charcot arthropathy); felixlai.md (Chronic arterial insufficiency, Acute arterial insufficiency)
Differential Diagnosis of Foot/Toe Pain
The differential diagnosis of foot and toe pain is wide — but manageable when you approach it systematically. Think of it as a two-step exercise: first, localise (where is the pain?), then categorise (what type of pathology?). A 70-year-old smoker with forefoot pain at rest is a completely different clinical problem from a 25-year-old runner with plantar heel pain. Context is everything.
I will present the DDx using the Murtagh diagnostic strategy framework (probability diagnosis → serious disorders not to be missed → pitfalls → masquerades → "is the patient telling me something?") and then organise by anatomical region for rapid clinical application.
1. Murtagh's Diagnostic Strategy for Foot/Toe Pain
This framework is gold for clinical reasoning — it forces you to think beyond the obvious.
Murtagh's Framework — Why Use It?
Murtagh's strategy is not just a list; it is a risk-stratification tool. You start with what is most likely (probability diagnosis), then systematically exclude what is most dangerous (serious disorders), account for commonly missed conditions (pitfalls), consider systemic disease masquerading as foot pain, and finally ask whether there is a psychosocial component. This ensures you never miss a limb- or life-threatening diagnosis while efficiently working up the common conditions.
These are the conditions you will see day-in, day-out:
| Condition | Why It's Common |
|---|---|
| Acute or chronic foot strain | Overuse, poor footwear, occupational standing — the foot bears the entire body weight and is subjected to enormous repetitive mechanical stress |
| Sprained ankle | The most common musculoskeletal injury globally; lateral ligament complex (ATFL → CFL → PTFL) is vulnerable during inversion injuries |
| Osteoarthritis (especially great toe — hallux rigidus) | 1st MTPJ endures massive loads during push-off; cartilage degeneration → pain and stiffness with dorsiflexion [1] |
| Plantar fasciitis | MC cause of infracalcaneal pain (80%) — repetitive strain at the calcaneal origin of the plantar fascia [6][8] |
| Achilles tendonopathy | Watershed zone 2–6 cm above insertion has poor blood supply → vulnerable to degenerative microtears [8] |
| Tibialis posterior tendonopathy | Main dynamic stabiliser of the medial longitudinal arch; degeneration → progressive flat foot with medial ankle pain [8] |
| Wart, corn or callus | Plantar warts (HPV type 1), corns and calluses from chronic friction/pressure — extremely common, especially with ill-fitting shoes [1][9] |
| Ingrowing toenail / paronychia | Improper nail trimming + tight footwear → nail edge penetrates periungual tissue → inflammation ± secondary infection [1] |
"Foot strain is probably the commonest cause of podalgia" [1]. "Podalgia" — from Greek pous (foot) + algos (pain). Don't overthink it — sometimes the foot just hurts because it has been overworked.
These are the ones that keep you up at night. Miss them and the patient loses a limb, or worse.
| Category | Conditions | Why Serious |
|---|---|---|
| Vascular insufficiency | Small vessel disease (PAD, diabetic angiopathy, Buerger's disease) → critical limb ischaemia → rest pain → gangrene [1][5] | Limb loss if not revascularised; DM accelerates disease by 2× and each 1% ↑ HbA₁c raises PAD risk by 26% [5] |
| Neoplasia / Cancer | Osteoid osteoma, osteosarcoma, synovial sarcoma, acral lentiginous melanoma [1] | Osteoid osteoma: benign but causes severe nocturnal pain; osteosarcoma: aggressive primary bone tumour; acral melanoma: most common melanoma subtype in Asians — easily missed on soles/nails |
| Infection (rare but devastating) | Septic arthritis, actinomycosis, osteomyelitis [1] | Septic arthritis destroys cartilage within days if untreated [3]; osteomyelitis in diabetic foot = major amputation risk |
| Rheumatoid arthritis | Symmetric MTPJ synovitis → erosions → forefoot destruction [1] | Progressive joint destruction if not treated with DMARDs early |
| Peripheral neuropathy | Diabetic, alcoholic, B₁₂ deficiency [1] | Loss of protective sensation → unrecognised injury → ulceration → infection → amputation (the "diabetic foot cascade") |
| Complex regional pain syndrome (CRPS) | Type I (no nerve injury) or Type II (with nerve injury) [1] | Chronic, severe, disproportionate pain with autonomic/trophic changes → severe disability if not recognised early |
| Ruptured Achilles tendon | Missed rupture → chronic weakness, abnormal gait [1] | Thompson test positive (no plantarflexion on calf squeeze) — if missed acutely, surgical outcomes are inferior [8] |
Never Miss
A hot, swollen joint = septic arthritis until proven otherwise, even without fever, ↑WBC, or ↑ESR/CRP [3]. Joint aspiration is mandatory. The distinction between gout and septic arthritis cannot be made clinically alone — they can look identical. And they can coexist (gout is itself a risk factor for septic arthritis because crystal-damaged cartilage is more vulnerable to bacterial seeding).
These are the conditions that are frequently misdiagnosed or overlooked:
| Condition | Why It's Missed |
|---|---|
| Ruptured tibialis posterior tendon | Insidious onset, patients often attribute it to "getting old"; the progressive flat foot and hindfoot valgus develop gradually. Look for "too many toes" sign from behind, inability to single-leg heel raise, flexible hindfoot valgus [1][8] |
| Foreign body (especially children) | Children may not give a clear history; a glass shard or thorn in the sole causes persistent pain. Always X-ray (glass is radiopaque!) [1] |
| Gout | Can mimic cellulitis or septic arthritis; serum urate may be normal or low during an acute flare (12–43% of cases) — so a normal uric acid does NOT rule out gout [1][3] |
| Morton neuroma | Burning interdigital pain often attributed to "metatarsalgia" or "neuritis" without specific diagnosis. Mulder's click is specific but not always performed [1] |
| Tarsal tunnel syndrome | Analogous to carpal tunnel but far less recognised; medial ankle/sole burning/tingling misattributed to plantar fasciitis or neuropathy [1] |
| Deep peroneal nerve (entrapment/injury) | Numbness in 1st web space + weakness of EDB; can occur from tight shoes or anterior tarsal tunnel compression [1] |
| Chilblains (pernio) | Cold-induced inflammatory lesions on toes — red/purple, itchy, painful papules. Common in HK winters (damp cold). Missed because clinicians don't think of it in a subtropical city, but HK's damp winters and lack of central heating make it surprisingly common [1] |
| Stress fracture (e.g. navicular) | Navicular stress fracture is notoriously occult on plain XR; needs MRI or bone scan. Common in running athletes. Delay in diagnosis → non-union because the navicular has poor central blood supply (analogous to scaphoid in the wrist) [1] |
| Erythema nodosum | Tender, red subcutaneous nodules on shins/feet. It is a reactive process (not a primary skin disease) — search for underlying cause: sarcoidosis, TB, IBD, Strep infection, drugs (OCP, sulfonamides) [1] |
Rarities (uncommon but examinable) [1]:
- Spondyloarthropathies (ankylosing spondylitis, psoriatic arthritis, reactive arthritis) — enthesitis at Achilles/plantar fascia insertions, dactylitis of toes [1][3]
- Osteochondritis: navicular (Köhler disease) in children 3–7y, metatarsal head (Freiberg disease) in adolescents (typically 2nd MT head), calcaneum (Sever disease) in 8–14y [1]
- Glomus tumour (under nail) — rare benign vascular tumour of glomus body; exquisitely tender subungual nodule with classic triad: pain, point tenderness, cold sensitivity. The pain is disproportionate to the tiny lesion [1]
- Paget disease — excessive disorganised bone remodelling; can affect calcaneus or metatarsals → bone pain, deformity, pathological fracture, elevated ALP [1]
These are systemic diseases that can present with foot pain as a primary complaint:
| Masquerade | How It Presents as Foot Pain |
|---|---|
| Diabetes | Peripheral neuropathy (burning/tingling feet, "glove and stocking"), diabetic foot ulcers, Charcot arthropathy, increased infection risk [1][4] |
| Drugs | Fluoroquinolones → Achilles tendinopathy/rupture; statins → myalgia; thiazides/loop diuretics → gout; colchicine → neuropathy/myopathy; isoniazid → peripheral neuropathy (B₆ depletion) [1] |
| Spinal dysfunction | L5 radiculopathy → foot drop + dorsal foot numbness; S1 radiculopathy → lateral foot pain + diminished ankle reflex + weakness of plantarflexion. Sciatica — pain radiating down posterior/lateral leg to foot/ankle from L5–S1 nerve root compression [1][7] |
"A non-organic cause warrants consideration with any painful condition" [1]
- Chronic foot pain without clear organic cause may reflect depression, anxiety, somatisation, secondary gain (compensation claims, work avoidance), or simply inadequate footwear education.
- Always screen for psychosocial factors — especially in chronic pain presentations.
This is the approach you'll use at the bedside. Once you've localised the pain, use this table to generate your differential:
3. Differentiating Key Conditions: Clinical Reasoning
This is a classic exam scenario. All three present with a hot, swollen, exquisitely tender joint. Here's how to tell them apart:
| Feature | Gout | Pseudogout (CPPD) | Septic Arthritis |
|---|---|---|---|
| Typical site | 1st MTPJ (podagra) > knee > ankle [3] | Knee (MC) > wrist > ankle; less commonly foot [3] | Knee > hip > ankle > wrist; 1st MTPJ less common [3] |
| Typical patient | M >> F, 4th–5th decade (M), 6th–7th decade (F) [3] | ↑ with age (rare < 55y), M ≈ F [3] | Any age; RF: IVDU, prosthetic joint, I/C, chronic arthritis, DM [3] |
| Crystal morphology | Needle-shaped, negative birefringent (yellow parallel to axis on polarised microscopy) [3] | Rhomboid, weakly positive birefringent (blue parallel to axis) [3] | No crystals (but gout + sepsis can coexist!) |
| Serum urate | Often elevated, but can be normal/low during acute flare (12–43%) [3] | Normal | Normal |
| Synovial fluid WBC | 2–100 × 10³/mL, > 90% neutrophils [3] | 15–30 × 10³/mm³, 90% neutrophils [3] | Usually > 50 × 10³/mL, > 90% neutrophils |
| Gram stain/culture | Negative | Negative | Positive (~50–70% sensitivity for Gram stain) |
| XR | Normal acutely; chronic: "rat-bite" erosions with overhanging edges, tophi [3] | Chondrocalcinosis (punctate/linear radiodensities in cartilage) [3] | Soft tissue swelling; late: joint space loss, erosion |
The Rule
Joint aspiration is the single most important test for an acutely swollen joint. You cannot reliably distinguish gout from septic arthritis clinically. Always send for Gram stain, culture, AND polarised microscopy. Remember that gout and septic arthritis can coexist — the presence of crystals does NOT exclude infection [3].
DDx of heel pain [8]:
- Plantar fasciitis (MC) — first-step morning pain, tenderness at medial calcaneal tuberosity
- Achilles tendinopathy / rupture — posterior heel, worse with activity, tenderness 2–6 cm above insertion
- Retrocalcaneal bursitis — pain deep to Achilles at its calcaneal insertion, pain with squeezing either side of Achilles ("squeeze test")
- Posterior ankle impingement (especially FHL) — posterior ankle pain in plantarflexion (dancers, ballet), flexor hallucis longus tenosynovitis
- Arthritis of ankle joint / subtalar joint — stiffness, reduced ROM, crepitus
Other differentials for heel pain not listed above:
- Calcaneal stress fracture — diffuse heel pain with "squeeze test" (mediolateral compression of calcaneus), common in runners, military recruits
- Fat pad atrophy — central plantar heel pain (not medial like plantar fasciitis), common in elderly; the calcaneal fat pad normally acts as a shock absorber, and atrophy exposes the calcaneus to direct ground-reaction forces
- Baxter's nerve entrapment — medial heel pain that is more posterior/lateral than plantar fasciitis; chronic, not typically "first-step" pattern
- Sever disease (calcaneal apophysitis) — in children 8–14y, pain at Achilles insertion onto the calcaneal apophysis; the apophysis is the last centre to fuse, and traction from the Achilles on the growing bone causes inflammation [1]
- Tarsal tunnel syndrome — burning/tingling on the sole ± medial heel, Tinel's positive behind medial malleolus
Already detailed in the previous section, but this is so high yield it bears repeating in the DDx context:
| Feature | Vascular Claudication | Neurogenic Claudication (Spinal Stenosis) |
|---|---|---|
| Cause | Chronic arterial insufficiency → exercise-induced muscle ischaemia | Spinal stenosis → compression of spinal arteries → lumbosacral root ischaemia |
| Claudication distance | Constant | Variable |
| Relief | "Shop window to shop window" — standing still | "Park bench to park bench" — flexion of spine (sitting/bending forward); going downstairs > upstairs |
| Rest pain | None (unless critical ischaemia) | May be present (prefer slight spinal flexion) |
| Other symptoms | Nil | Paraesthesia, numbness, weakness |
| Pulses | Absent/diminished distally | Normal |
Why does spinal flexion relieve neurogenic claudication? Because flexing the lumbar spine opens the spinal canal and neural foramina (the canal is narrowest in extension), decompressing the cauda equina [5].
Rest pain of critical limb ischaemia must be distinguished from peripheral neuropathy [5]:
| Feature | Rest Pain (CLI) | Peripheral Neuropathy |
|---|---|---|
| Distribution | Toes and forefoot (least perfused area) | Bilateral, glove-and-stocking pattern |
| Character | Continuous, severe aching | Burning, neuropathic (shooting, electric) |
| Positional | ↑ lying flat, ↓ dependent | Not positional |
| Pulses | Absent/diminished | Usually present |
| Skin | Pale, atrophic, hair loss, gangrene | May be normal or with trophic changes |
| Feature | Embolism | Thrombosis-in-situ |
|---|---|---|
| Common causes | Cardiac origin (80%): AF, MI (LV mural thrombus), valvular heart disease / prosthesis; AAA (blue toe / trash foot) | Atherosclerosis (acute plaque rupture in PVD), aortic dissection, hypercoagulability (malignancy, APLS, sepsis), Buerger disease |
| Severity | Complete ischaemia (no collaterals) | Incomplete ischaemia (collaterals) |
| Onset | Hyperacute (seconds to minutes) | Acute (hours or days) |
| History/PE | Embolic source identifiable (e.g. AF); contralateral limb pulses present; absent bruits | Previous claudication; PVD in contralateral limb (e.g. absent pulse); present bruits |
| Angiography | Minimal atherosclerosis; sharp cut-off with few collaterals | Diffuse atherosclerosis; irregular cut-off with well-developed collaterals |
Clinical features of acute limb ischaemia — the 6 Ps [7]:
- Pain (early — nerves are most sensitive to ischaemia)
- Pallor (limb colour progresses: 0–6 h = "marble white" pallor → 6–12 h = blanchable mottling → > 12 h = fixed mottling = irreversible)
- Perishingly cold
- Pulseless
- Paraesthesia
- Paralysis (late — indicates muscle infarction, poor prognosis)
DDx of acute limb ischaemia [7]:
- Acute extremity compartment syndrome
- DVT with superficial vein thrombosis (phlegmasia cerulea dolens)
| Feature | Plantar Wart (Verruca Plantaris) | Corn / Callus |
|---|---|---|
| Cause | HPV type 1 infection [9] | Chronic friction / pressure |
| Appearance | Slightly protruding, rough surface, horny rim [9]; obscures normal skin lines (dermatoglyphics) | Well-demarcated thickening; corn has central conical core |
| Pain pattern | Pain with lateral squeeze (compressing blood vessels within the lesion) | Pain with direct pressure (central core presses on dermis) |
| On paring | Thrombosed capillaries visible (black/red dots) — pinpoint bleeding [9] | No thrombosed capillaries; translucent core |
| Skin lines | Disrupted/obscured | May be preserved or obscured, but no capillary dots |
| Feature | Charcot Arthropathy | Cellulitis | Osteomyelitis | DVT | Gout |
|---|---|---|---|---|---|
| Pain | Painless or minimal (neuropathy!) [4] | Painful | Variable (may be reduced in DM) | Calf pain/tenderness | Exquisite pain |
| Warmth | +++ | +++ | + | + | +++ |
| Swelling | +++ (midfoot/ankle) | Diffuse | Localised | Unilateral pitting | Joint/periarticular |
| Systemic signs | None | Fever, ↑WBC | Fever (may be absent) | Low-grade fever | Fever possible |
| Sensation | Impaired (insensate foot) | Normal | May be impaired in DM | Normal | Normal |
| Key investigation | XR (degenerative changes, subluxation); MRI or bone scan if XR inconclusive; joint aspiration to rule out DDx [4][8] | Clinical | Probe-to-bone test, MRI, biopsy | Duplex USG | Joint aspiration (crystals) |
4. Key History and Examination for DDx [1]
"Ask about the quality of the pain, its distribution, mode of onset, periodicity, relationship to weight-bearing and associated features such as swelling or colour change. Enquire about pain in other joints including sacroiliac joints." [1]
- Quality: Burning (neuropathic), cramping (vascular), sharp/stabbing (mechanical), deep/boring (bone), aching (inflammatory)
- Distribution: Localised (fracture, OA, gout) vs. diffuse (neuropathy, PAD, inflammatory arthritis)
- Mode of onset: Acute (fracture, gout, septic arthritis, acute ischaemia) vs. gradual (plantar fasciitis, OA, PAD, neuropathy)
- Periodicity: Morning stiffness > 30 min (inflammatory arthritis); first-step pain (plantar fasciitis); nocturnal (gout, osteoid osteoma, rest pain)
- Relationship to weight-bearing: Worse with (mechanical, stress fracture, plantar fasciitis); not related (rest pain, neuropathy, gout at rest)
- Colour change: White → blue → red (Raynaud's); black (gangrene); red/erythematous (gout, cellulitis, Charcot)
- Sacroiliac / other joints: screening for spondyloarthropathy if young patient with enthesitis or dactylitis [1]
"Follow the inspection, palpation, movement and test function approach. Test active and passive movements of the ankle (talar) joint, hindfoot (subtalar) joint and mid-foot (midtarsal) joint." [1]
"Check the peripheral circulation and perform a neurological examination including sensation, motor strength and reflexes." [1]
Consider: FBE, ESR/CRP, rheumatoid arthritis tests, blood glucose, uric acid, nerve conduction studies and imaging (e.g. plain X-ray — compare both sides), ultrasound, MRI, radionuclide scans. [1]
| Scenario | Top DDx |
|---|---|
| Young athlete with gradual forefoot pain worsening with running | Metatarsal stress fracture, Morton neuroma, sesamoiditis |
| Middle-aged man waking at night with explosive 1st MTPJ pain | Gout (podagra) |
| Elderly diabetic with painless midfoot swelling and deformity | Charcot arthropathy |
| Elderly smoker with forefoot pain at rest, relieved by dangling leg | Critical limb ischaemia (rest pain) |
| Runner with plantar heel pain worst with first morning steps | Plantar fasciitis |
| Child 8–14y with posterior heel pain after sports | Sever disease (calcaneal apophysitis) |
| Young woman with progressive flat foot and medial ankle pain | Tibialis posterior tendon dysfunction |
| Post-menopausal woman with painful, stiff great toe | Hallux rigidus (OA 1st MTPJ) |
| Young man with Achilles heel pain + dactylitis + low back stiffness | Spondyloarthropathy (enthesitis) |
| Diabetic with foot ulcer, probe touches bone | Osteomyelitis |
| Pigmented lesion under toenail in Chinese patient | Acral lentiginous melanoma (until proven otherwise) |
| Sudden pale, pulseless, cold leg in patient with AF | Acute arterial embolism |
High Yield Summary
Murtagh's framework for foot pain:
- Probability: Foot strain, sprained ankle, OA (hallux rigidus), plantar fasciitis, Achilles tendonopathy, tibialis posterior tendonopathy, warts/corns/calluses, ingrown toenail
- Serious: Vascular insufficiency (PAD/Buerger), neoplasia (osteoid osteoma, osteosarcoma, acral melanoma), infection (septic arthritis, osteomyelitis), RA, peripheral neuropathy, CRPS, ruptured Achilles
- Pitfalls: Ruptured tibialis posterior, foreign body, gout, Morton neuroma, tarsal tunnel syndrome, chilblains, stress fracture (navicular), erythema nodosum
- Rarities: Spondyloarthropathies, osteochondritis (Köhler, Freiberg, Sever), glomus tumour, Paget disease
- Masquerades: Diabetes, drugs (fluoroquinolones, diuretics), spinal dysfunction (L5/S1 radiculopathy)
- Non-organic: Always consider psychosocial factors in chronic foot pain
Key DDx principles:
- Hot swollen joint → aspirate → crystals (gout/pseudogout) vs. bacteria (septic arthritis) — they can coexist
- Heel pain → plantar fasciitis is MC (80%) but don't forget Achilles, calcaneal fracture, Sever disease, tarsal tunnel, Baxter's nerve
- Rest pain in foot → critical limb ischaemia vs. peripheral neuropathy (bilateral + glove-stocking vs. unilateral + positional)
- Acute limb ischaemia → 6 Ps; differentiate embolism (AF, acute, complete) vs. thrombosis (chronic PVD, subacute, incomplete)
- Wart vs. corn → lateral squeeze (wart) vs. direct pressure (corn); thrombosed capillaries on paring (wart)
- Warm swollen painless foot in diabetic → Charcot arthropathy (not cellulitis!)
Active Recall - Differential Diagnosis of Foot/Toe Pain
References
[1] Lecture slides: murtagh merge.pdf (p55–57, Foot and ankle pain) [3] Senior notes: Ryan Ho Rheumatology.pdf (p28, Approach to Acute Monoarthritis; p35–37, Gout; p41–42, CPPD; p63, Peripheral SpA; p67, Septic Arthritis; p138, Viral Warts) [4] Senior notes: Ryan Ho Endocrine.pdf (p98–99, Diabetic Foot, Diabetic Neuropathy, Charcot Arthropathy) [5] Senior notes: Ryan Ho Cardiology.pdf (p205–207, Intermittent Claudication, Rest Pain; p210, Acute Limb Ischaemia) [6] Senior notes: felixlai.md (Chronic arterial insufficiency, Acute arterial insufficiency, Gangrene) [7] Senior notes: maxim.md (Acute limb ischaemia, Approach to spine diseases) [8] Senior notes: maxim.md (Achilles tendinopathy and rupture, Plantar fasciitis, DDx of heel pain, Diabetic foot ulcers, Charcot arthropathy, Hallux valgus, Pes planus, Pes cavus) [9] Senior notes: felixlai.md (Warts/verruca section)
Diagnostic Criteria, Algorithm, and Investigations for Foot/Toe Pain
Foot and toe pain is not a single disease — it is a localisation-and-categorisation problem. There is no single "diagnostic criterion" for "foot pain" the way there is for, say, rheumatoid arthritis. Instead, your diagnostic approach must be condition-specific, driven by the clinical picture you have built from history and examination. What I will give you here is: (1) the formal diagnostic criteria for the key conditions that present as foot/toe pain, (2) a master diagnostic algorithm you can apply at the bedside, and (3) a comprehensive run-through of every investigation modality with its key findings and interpretation.
1. Diagnostic Criteria for Key Conditions Causing Foot/Toe Pain
This is the most important set of diagnostic criteria you need to know for a painful 1st MTPJ. The 2015 criteria use a scoring system (out of a possible 23 points); a score ≥ 8 classifies gout.
Entry criterion (mandatory): At least 1 episode of swelling, pain, or tenderness in a peripheral joint or bursa.
Sufficient criterion (if met, no further scoring needed): Detection of MSU crystals in a symptomatic joint/bursa or tophus → this is definitive — if you aspirate and find crystals, the diagnosis is made [3][10].
If crystal analysis is not available, use the scoring domains:
| Domain | Category | Score |
|---|---|---|
| Pattern of joint involvement | Ankle or midfoot (monoarticular) | +1 |
| 1st MTPJ involvement | +2 | |
| Characteristics of episode | Erythema over joint | +1 |
| Cannot bear touch/pressure | +1 | |
| Great difficulty walking/unable to use joint | +1 | |
| Time to maximal pain < 24 hours | ≥ 2 of 3 typical features: +3 | |
| Resolution ≤ 14 days | ≥ 2 of 3: +3 | |
| Complete resolution between episodes | ||
| Clinical evidence of tophi | Draining or chalk-like subcutaneous nodule under transparent skin, often with overlying vascularity | +4 |
| Serum urate | < 4 mg/dL ( < 0.24 mmol/L) | −4 |
| 6– < 8 mg/dL (0.36– < 0.48) | +2 | |
| 8– < 10 mg/dL (0.48– < 0.60) | +3 | |
| ≥ 10 mg/dL (≥ 0.60) | +4 | |
| Imaging | USG double contour sign or DECT urate deposition | +4 |
| XR: ≥ 1 erosion (hands/feet) with characteristic "rat-bite" overhanging margins | +4 |
Score ≥ 8 = classified as gout [3].
Crucial Nuance
Serum urate can be normal or low during an acute flare (12–43% of cases) [3]. A normal urate does NOT rule out gout. Serum urate should ideally be deferred to ≥ 2 weeks after resolution of the acute episode for accuracy [3]. The single most important test remains joint fluid analysis with polarised microscopy showing needle-shaped, negatively birefringent MSU crystals.
There is no formal points-based classification like gout. Diagnosis is based on arthrocentesis + imaging [3]:
- Definite CPPD disease: Positively birefringent crystals on polarised light microscopy + cartilage/joint capsule calcification (chondrocalcinosis) on XR; OR CPP crystals identified by definitive analytical means [3]
- Probable CPPD disease: Either positive birefringent crystals on polarised LM alone; OR chondrocalcinosis on XR alone [3]
Crystal morphology — why does birefringence differ?
- "Birefringence" = the ability of a crystal to split polarised light into two rays. MSU crystals are strongly negatively birefringent (yellow when parallel to the compensator axis); CPPD crystals are weakly positively birefringent (blue when parallel). The physical basis is the molecular arrangement of the crystal lattice — the elongated needle shape of urate vs. the rhomboid shape of pyrophosphate creates different optical properties.
There are no formal "classification criteria" — this is a clinical and microbiological diagnosis:
- "A hot, swollen tender joint = septic arthritis until proven otherwise, even without fever, ↑WBC, ↑ESR/CRP" [3]
- Gold standard: Joint aspiration → Gram stain (urgent), culture, cell count
- Synovial WBC > 50,000/mm³ (with > 90% neutrophils) is highly suggestive
- Gram stain sensitivity ~50–70%; culture is more sensitive but takes time
- Blood cultures: positive in ~50% of non-gonococcal cases
| Category | Sensory Loss | Muscle Weakness | Arterial Signal | Venous Signal | Treatment |
|---|---|---|---|---|---|
| Viable (I) | None | None | Audible | Audible | Imaging |
| Marginally threatened (IIa) | Minimal (toes) | None | Inaudible | Audible | Urgent revascularisation |
| Immediately threatened (IIb) | Beyond toes | Partial | Inaudible | Audible | Emergency revascularisation |
| Non-viable (III) | Completely anaesthetic | Completely paralysed | Inaudible | Inaudible | Amputation |
Why is this classification based on sensory loss, motor function, and Doppler signals? Because these reflect the progressive ischaemic cascade: nerves are most sensitive to ischaemia (sensory loss first), then muscle (weakness/paralysis late = irreversible damage), and arterial/venous Doppler signals indicate the degree of perfusion compromise [5].
There are no formal "classification criteria." Plantar fasciitis is a clinical diagnosis [8]:
- Plantar heel pain with weight-bearing, radiating down the arch
- Pain worsens with first few steps in the morning (after inactivity) and with toe dorsiflexion
- Tenderness over plantar fascia up to calcaneal tuberosity
- Investigations: clinical diagnosis; XR to rule out fracture + may show plantar heel spur (but note: the heel spur itself is an incidental finding in ~15–25% of the asymptomatic population and is NOT the cause of pain — it merely indicates chronic traction at the fascia origin) [8]
Already detailed in the prior section. Key diagnostic thresholds for workup:
Measured on AP weight-bearing XR [8]:
- Hallux valgus angle (normal < 15°): angle between 1st MT shaft and proximal phalanx
- Mild: 15–20°
- Moderate: 21–39°
- Severe: > 40°
- Intermetatarsal angle (normal < 9°): angle between 1st and 2nd MT shafts
- Also assess for OA of the 1st MTPJ (joint space narrowing, osteophytes)
- XR foot and ankle for Meary's angle (talo-1st metatarsal angle) [8]
- Normal: 0° (the talus axis and 1st MT axis are co-linear)
- > 4° = pes planus (flat foot) — the angle is convex plantarward, indicating arch collapse
Here is a practical bedside algorithm. The key decision points are: localise → temporality → vascular check → inflammatory vs. mechanical → specific investigations.
Key Decision Points in the Algorithm
- Always check pulses and ABI first in any diffuse or forefoot pain — you cannot afford to miss PAD.
- Any hot, swollen joint must be aspirated — you cannot distinguish gout from septic arthritis without synovial fluid analysis.
- Plain XR is the first-line imaging for most foot conditions — it is readily available, has the highest spatial resolution for bony detail, and can reveal fractures, arthritic changes, and chondrocalcinosis.
- MRI is the problem-solver when XR is negative but clinical suspicion remains high (stress fracture, early osteomyelitis, soft tissue pathology, Lisfranc injury).
3. Investigation Modalities — Comprehensive Guide
I will organise investigations by modality, explaining what each test actually measures, when to use it, and how to interpret the findings.
| Test | What It Measures | Key Findings | When to Use |
|---|---|---|---|
| Ankle-Brachial Index (ABI) | Ratio of ipsilateral ankle systolic BP (higher of dorsalis pedis or posterior tibial) to higher arm systolic BP [5][7] | Normal: 0.90–1.30; Claudication: 0.40–0.90; Rest pain/tissue loss: < 0.4; Calcified: > 1.30 [5] | Any suspected PAD. DM patients should be screened every 5 years [5] |
| Toe-Brachial Index (TBI) | Ratio of toe systolic pressure to arm systolic pressure, using a small cuff on the great toe | Normal ≥ 0.7; < 0.7 suggests PAD | When ABI > 1.30 (calcified vessels in DM/ESRD) — digital arteries are less frequently calcified, so TBI is more reliable [5][7] |
| Transcutaneous oxygen pressure (TcPO₂) | Measures partial pressure of oxygen diffusing through the skin — reflects local tissue perfusion and oxygenation | > 30 mmHg: adequate wound-healing potential; < 30 mmHg: poor healing [8] | Diabetic foot ulcers — assesses whether there is sufficient perfusion for wound healing before deciding on conservative vs. surgical management [8] |
| Exercise ABI | ABI measured after treadmill exercise (standardised: 3.2 km/h, 12% incline for 5 min or until symptoms) | > 0.2 drop in ABI from baseline = significant arterial disease equivalent to claudication [5] | ABI normal at rest but patient is symptomatic — exercise unmasks flow-limiting stenosis that is compensated at rest [5] |
| Monofilament test (Semmes-Weinstein 10g) | Tests small-fibre sensation — the 10g monofilament is pressed against the plantar surface until it buckles; patient reports if they feel it | Loss of sensation = neuropathy; inability to feel 10g monofilament = loss of protective sensation | Diabetic foot screening — loss of monofilament sensation is a key risk factor for ulceration [4] |
| Tuning fork test (128 Hz) | Tests large-fibre (vibration) sensation | Loss of vibration sense distally in a "stocking" pattern | Diabetic neuropathy screening — monofilament (small fibre) + tuning fork (large fibre) together [4] |
| Probe-to-bone test | Sterile blunt metal probe inserted into a diabetic foot ulcer | If probe reaches bone → specificity ~89% for osteomyelitis | Any diabetic foot ulcer — simple, bedside, cheap, and highly informative |
Why is ABPI not useful in DM? Because chronic hyperglycaemia promotes Mönckeberg medial arterial calcification — calcium deposits in the tunica media make the vessel wall incompressible. When you inflate the cuff, you need higher pressure to occlude a calcified artery, giving a falsely high reading. The digital arteries (measured by TBI) are usually spared from this calcification because they are small and less susceptible to Mönckeberg sclerosis [5][7][8].
"Consider: FBE, ESR/CRP, rheumatoid arthritis tests, blood glucose, uric acid" [1]
| Test | What It Tells You | Key Findings / Interpretation |
|---|---|---|
| FBE (Full Blood Examination / CBC) | Infection, inflammation, malignancy | Leukocytosis (neutrophil predominant): septic arthritis, gout flare, cellulitis, osteomyelitis. Anaemia: chronic disease (RA, malignancy). Thrombocytosis: reactive in chronic inflammation |
| ESR / CRP | Non-specific markers of inflammation | ↑↑ in inflammatory/infective conditions (septic arthritis, gout flare, RA flare, osteomyelitis, cellulitis) [10]. CRP rises and falls faster than ESR — useful for monitoring acute response. CRP usually normal/mildly ↑ in SLE [10] |
| Serum urate (uric acid) | Serum urate level | Hyperuricaemia supports gout diagnosis BUT normal/low levels do not exclude it (12–43% normal/low during acute flare). Should be deferred to ≥ 2 weeks after resolution for accuracy [3] |
| Blood glucose / HbA₁c | DM screening / glycaemic control | DM is a masquerade — causes neuropathy, PAD, foot ulcers, Charcot arthropathy, increased infection risk [1][4]. HbA₁c also predicts PAD risk (26% ↑ risk per 1% ↑ HbA₁c) [5] |
| RF (Rheumatoid Factor) | Anti-IgG IgM antibody | +ve in ~70% RA but not specific (also +ve in Sjögren's, SLE, infections, hepatitis C, healthy elderly). A negative RF does not exclude RA [10] |
| Anti-CCP (anti-citrullinated peptide antibody) | Specific marker for RA | More specific than RF (~95% specificity). If both RF and anti-CCP are positive → very high specificity for RA [10] |
| HLA-B27 | Genetic marker associated with spondyloarthropathies | Positive in ~90% AS, ~50% PsA with axial disease, ~50–80% reactive arthritis. NOT diagnostic alone — used to support clinical picture |
| Calcium, phosphate, Mg, ALP, ferritin | Screen for metabolic causes of CPPD | CPPD disease associated with hyperparathyroidism (3.35×), hypomagnesaemia, hypophosphatasia, haemochromatosis (ferritin) — should be screened after diagnosis of CPPD [3] |
| CK, LDH | Muscle damage | ↑ in compartment syndrome, rhabdomyolysis (reperfusion injury after acute ischaemia) |
"Joint fluid analysis: MOST IMPORTANT TEST" [10]
Indications [10]:
- Suspicious of septic arthritis
- Suspicious of crystal-induced arthritis
- Suspicious of haemarthrosis
- Differentiating inflammatory vs. non-inflammatory arthritis
Send for [10]:
- Macroscopic: colour, viscosity, turbidity
- Microscopy: wet films, WBC count/differential, crystal microscopy
- Microbiology (if suspect septic arthritis): Gram stain (URGENT), bacterial culture, AFB smear and culture, fungal stain if indicated
Interpretation of synovial fluid:
| Parameter | Normal | Non-inflammatory (e.g. OA) | Inflammatory (Gout, RA) | Septic |
|---|---|---|---|---|
| Colour | Clear, colourless | Clear, yellow | Cloudy, yellow-green | Turbid, purulent |
| Viscosity | High | High | Low (enzymes degrade hyaluronic acid) | Very low |
| WBC/mm³ | < 200 | < 2,000 | 2,000–100,000 | > 50,000 (often > 100,000) |
| % Neutrophils | < 25% | < 25% | > 50% (often > 90%) | > 90% |
| Crystals | None | None | MSU: needle-shaped, −ve birefringent; CPPD: rhomboid, +ve birefringent [3][10] | None (unless co-existing crystal disease) |
| Gram stain | −ve | −ve | −ve | +ve in ~50–70% |
| Culture | −ve | −ve | −ve | +ve |
Why is viscosity LOW in inflammatory effusions? Because the intense neutrophilic inflammation releases lysosomal enzymes (including hyaluronidase) that degrade hyaluronic acid — the glycosaminoglycan that gives synovial fluid its normal high viscosity and "stringy" consistency. In OA (non-inflammatory), the synovium is not heavily infiltrated, so hyaluronic acid is preserved.
Crystal Microscopy Memory Aid
MSU (gout): Needle-shaped, Negatively birefringent → Yellow when parallel to the compensator. Mnemonic: "Needles are Negative" (both start with N).
CPPD (pseudogout): Rhomboid, weakly Positively birefringent → Blue when parallel. Mnemonic: "Pseudogout is Positive and has P-shape (Pleomorphic/rhomboid)".
3.4 Imaging Modalities
"Good quality plain X-rays are important if there is doubt about the diagnosis of a painful foot" [1].
Why is XR the first-line imaging? It has the highest spatial resolution of any imaging modality — excellent for fine bony detail (fracture lines, erosions, osteophytes, calcifications). It distinguishes the four basic densities: calcium (white), water/soft tissue (grey), fat (dark grey), air (black) [11]. It is also fast, cheap, and universally available.
Key principle: Always get ≥ 2 views (most fractures may only be detected in one view due to the 2D representation of 3D structures) [11]. For the foot: AP and lateral (± oblique for midfoot/forefoot).
| Condition | Key XR Findings | Why |
|---|---|---|
| Hallux valgus | HV angle > 15°, intermetatarsal angle > 9° on AP weight-bearing view [8]; OA changes at 1st MTPJ | Weight-bearing is essential because it loads the arch and reveals the true degree of deformity |
| Hallux rigidus | Dorsal osteophytes at 1st MTPJ, joint space narrowing, subchondral sclerosis | OA changes from chronic cartilage wear |
| Gout (chronic) | "Rat-bite" erosions with overhanging edges (the tophus erodes bone from outside the joint margin, leaving a characteristic overhanging lip of cortex); soft tissue swelling; preserved joint space until late (unlike RA) | MSU crystals deposit in periarticular soft tissue → granulomatous inflammatory response → external pressure erosion. Joint space is preserved because the inflammatory pannus is less destructive to cartilage than in RA [3] |
| CPPD | Chondrocalcinosis: irregular faint punctate/linear radiodensities in articular cartilage ± degenerative changes (subchondral cysts, osteophytes, ↓ joint space) [3] | CPP crystals deposit within hyaline cartilage and fibrocartilage → calcification visible on XR |
| RA | Periarticular osteopenia, symmetric joint space narrowing, marginal erosions at MTPJs (especially 5th MTPJ — the earliest site); no osteophytes (inflammatory arthritis lacks the repair response that produces osteophytes in OA) | Pannus formation → synovial hypertrophy → enzymatic destruction of cartilage and bone |
| Plantar fasciitis | Plantar heel spur (calcaneal enthesophyte) — but NOT diagnostic (present in 15–25% of asymptomatic population). Main role: rule out calcaneal fracture [8] | The spur represents chronic traction calcification at the plantar fascia origin — it is a marker of chronic stress, not the cause of pain |
| Pes planus | Meary's angle (talo-1st MT angle) > 4° [8]; talar uncovering at talonavicular joint | Arch collapse changes the alignment of talus relative to 1st MT — the co-linear relationship is lost |
| Stress fracture | May be normal on initial XR (callus/periosteal reaction takes 2–3 weeks to appear). Late: periosteal reaction, callus, fracture line | Repetitive microtrauma → microfractures → repair with callus. Early on, the damage is too microscopic for XR resolution |
| Lisfranc injury | Diastasis between 1st and 2nd MT bases on AP weight-bearing view (> 2 mm); fleck sign (small avulsion fracture at Lisfranc ligament attachment) | Disruption of the Lisfranc ligament (medial cuneiform → 2nd MT base) → loss of the rigid linkage → bones splay apart under body weight |
| Charcot arthropathy | Early: soft tissue swelling, loss in joint spaces. Late: forefoot bone resorption, disappearance in MT heads, pencil-pointing of phalangeal/MT shafts, subluxation/dislocations, stress fractures [4][8] | Progressive unrecognised joint destruction from absent pain feedback. "Pencil-pointing" = resorption of the articular ends |
| Calcaneal fracture | Böhler's angle (normally 25–40°) flattened or reversed; intra-articular extension into subtalar joint | Axial load compresses the posterior tuberosity and primary fracture line drives into the subtalar joint |
| Osteoid osteoma | Central radiolucent nidus ( < 2 cm) surrounded by dense reactive sclerosis | Prostaglandin-producing nidus induces surrounding reactive bone formation |
| 5th MT base fracture | Avulsion fracture at base (transverse orientation) vs. Jones fracture at metadiaphyseal junction (transverse, may show sclerosis in chronic cases) | Avulsion: peroneus brevis pulls off the base during inversion. Jones: stress at the watershed zone of blood supply → prone to non-union |
Advantages: Non-invasive, no radiation, real-time, dynamic assessment, can guide interventions (aspirations, injections). Disadvantages: Operator-dependent, limited bone visualisation, poor for deep structures.
| Condition | Key USG Findings |
|---|---|
| Morton's neuroma | Hypoechoic ovoid mass in the intermetatarsal space; positive Mulder's click under dynamic scanning |
| Plantar fasciitis | Thickened plantar fascia (> 4 mm at calcaneal insertion); hypoechoic echotexture; perifascial fluid |
| Achilles tendinopathy | Tendon thickening; hypoechoic areas (degeneration); neovascularisation on Doppler (colour Doppler shows increased flow in the degenerate tendon) |
| Achilles rupture | Discontinuity of tendon fibres; haematoma in the gap |
| Gout | Double contour sign: hyperechoic irregular band on the surface of articular cartilage (MSU crystal deposition on cartilage surface) — distinct from the subchondral bone echo [3]. Also: tophi (hyperechoic aggregates), erosions |
| CPPD | Thin hyperechoic band WITHIN the cartilage (paralleling the bone cortex, separated by hypoechoic cartilage) [3] — vs. gout double contour which is ON the cartilage surface |
| Joint effusion | Anechoic fluid distending the joint capsule — guides aspiration |
| Cellulitis / abscess | Cellulitis: diffuse subcutaneous oedema (cobblestone pattern). Abscess: hypoechoic collection with rim enhancement — guides I&D [3] |
| Tibialis posterior tendon | Tenosynovitis (fluid around tendon sheath); tendon thickening, tears, or complete rupture |
| Duplex USG (for PAD) | First-line imaging for all PAD patients [5]. B-mode locates occlusion; Doppler detects flow abnormalities. Normal arterial flow = triphasic (forward systolic + reverse early diastolic + forward late diastolic). Biphasic = single-level occlusion. Monophasic = multi-level occlusion [5] |
Why is normal arterial flow triphasic? The three phases reflect the physiology of peripheral arterial flow: (1) systolic forward flow driven by ventricular contraction, (2) brief early diastolic reverse flow due to elastic recoil of the arterial wall and high peripheral resistance in resting muscle, and (3) late diastolic forward flow as the elastic recoil propels blood forward again. Disease stiffens the artery and reduces compliance → loss of the reverse component → biphasic; severe disease reduces all pulsatility → monophasic [5].
Advantages: Best soft tissue contrast of any imaging modality; no ionising radiation; multiplanar. Disadvantages: Expensive, time-consuming, contraindicated with certain metallic implants, claustrophobia.
MRI is the problem-solver — used when XR is non-diagnostic but clinical suspicion is high.
| Condition | Key MRI Findings | Why MRI? |
|---|---|---|
| Stress fracture (esp. navicular) | Bone marrow oedema (hypointense T1, hyperintense T2/STIR) along the fracture line | XR is often normal in the first 2–3 weeks; MRI detects early bone oedema with > 95% sensitivity |
| Plantar fasciitis (refractory) | Thickened plantar fascia with increased T2 signal at the calcaneal insertion; peri-fascial oedema | Usually not needed (clinical diagnosis), but useful if refractory to treatment to rule out plantar fascia tear, plantar fibromatosis |
| Osteomyelitis | Bone marrow oedema (T1 low, T2/STIR high); cortical destruction; soft tissue abscess; contrast enhancement | MRI is the best imaging modality to differentiate cellulitis from osteomyelitis [3]. Sensitivity and specificity both ~90% |
| Charcot arthropathy | Bone marrow oedema, joint effusions, ligamentous disruption, subluxation | XR may be inconclusive early; MRI or bone scan if XR inconclusive [4][8] |
| Lisfranc injury (subtle) | Disruption of the Lisfranc ligament (normally a dark band connecting medial cuneiform to 2nd MT base on T1); bone bruising pattern | Weight-bearing XR may miss purely ligamentous injuries — MRI detects soft tissue disruption |
| Morton's neuroma | T1 low signal, T2 low-intermediate signal mass in the intermetatarsal space (the fibrous tissue is dense, so it is LOW signal even on T2 — unusual for a "mass") | USG is usually sufficient; MRI reserved for equivocal cases or pre-surgical planning |
| Achilles tendinopathy/partial tear | Tendon thickening; intratendinous signal change (increased T2 in partial tear); intact posterior margin in tendinosis | Differentiates tendinosis (degenerative) from partial tear (requires different management) |
| Tarsal tunnel syndrome | Space-occupying lesion within the tarsal tunnel (ganglion, accessory muscle, varicosities); tibial nerve oedema | Identifies the cause of compression when clinical diagnosis is confirmed by NCS |
| Tumours (osteoid osteoma, sarcoma, melanoma) | Nidus of osteoid osteoma (small enhancing focus); soft tissue mass extent; bone marrow involvement | Essential for staging and surgical planning |
| Indication | Key Findings |
|---|---|
| Calcaneal fracture | CT is the gold standard for calcaneal fractures — axial and coronal reformats show the fracture pattern, subtalar joint involvement, and guide surgical planning (Sanders classification) |
| Lisfranc injury (bony detail) | Subtle fracture-dislocations missed on XR; CT provides excellent bony detail |
| Tarsal coalition | Calcaneonavicular or talocalcaneal coalition (bony bar or fibrous bridge) |
| CT angiography (CTA) | Less invasive alternative to DSA for PAD; shows vessel stenosis/occlusion, collateral pathways. Risks: contrast allergy, nephropathy, radiation [7] |
"Gold standard" for arterial imaging [7]:
- Indicated only for patients with planned intervention (angioplasty/stenting) — it is both diagnostic AND therapeutic
- Inject radio-opaque dye into the arterial tree (usually via femoral artery) → imaging digitised by computer [7]
- Can be done intra-operatively to guide endovascular intervention [7]
- Risks: contrast allergy, contrast nephropathy, arterial injury (dissection, embolism, pseudoaneurysm) [7]
For Buerger's disease: angiogram shows corkscrew appearance of arteries (vascular damage) and tree root appearance of collaterals (vascular occlusion) [5]
| Indication | Findings |
|---|---|
| Occult stress fracture | Focal increased uptake at fracture site (high sensitivity but low specificity) |
| Osteomyelitis vs. Charcot | Three-phase bone scan: Charcot and osteomyelitis both show increased uptake in all three phases, so differentiation is difficult. Labelled WBC scan (In-111 or Tc-99m HMPAO) is more specific for infection (WBCs accumulate at infection site) |
| Charcot arthropathy | MRI or bone scan if XR inconclusive [4][8] |
"Consider: nerve conduction studies" [1]
| Test | What It Measures | When to Use | Key Findings |
|---|---|---|---|
| NCS | Large fibre conduction function by electrical stimulation of peripheral nerve and recording of response [12] | Tarsal tunnel syndrome, Morton's neuroma (controversial), diabetic neuropathy, peripheral neuropathy of any cause [1][12] | Slowed conduction velocity (demyelination) or reduced amplitude (axonal loss). In tarsal tunnel: prolonged distal motor/sensory latency of tibial nerve |
| EMG | Bioelectric activity of muscles — detects denervation | Myopathy vs. neuropathy; severity assessment | Fibrillation potentials, positive sharp waves (denervation); reduced recruitment (neuropathy); early recruitment with small polyphasic MUAPs (myopathy) |
NCS is useful for [12]: differentiation between focal and multifocal neuropathy; demyelinating vs. axonal neuropathy; assessment of severity; monitoring progress and treatment response. NCS is NOT useful for [12]: excluding neuropathy (clinical findings should suffice); defining the aetiology of neuropathy; cervical myelopathy (does not assess CNS function).
- A newer modality that can directly visualise MSU crystal deposits in tissues without joint aspiration
- Indicated in the ACR/EULAR gout criteria as imaging evidence of urate deposition [3]
- Not widely available but increasingly used in HK tertiary centres
| Test | Indication | Finding |
|---|---|---|
| Wood's lamp | Erythrasma (toe webs) [3] | Coral-red fluorescence — Corynebacterium minutissimum produces porphyrins that fluoresce under UV |
| Dermoscopy | Plantar warts vs. corns | Thrombosed capillaries appear as homogeneous black/red dots in warts; no such finding in corns |
| Compartment pressure measurement | Suspected foot compartment syndrome | Pressure ≥ 30 mmHg or within 30 mmHg of diastolic BP → fasciotomy indicated [5] |
| Condition | First-Line Investigation | Second-Line / Confirmatory | Key Diagnostic Finding |
|---|---|---|---|
| Gout | Joint aspiration + polarised microscopy | USG (double contour), DECT, serum urate (after 2 weeks) | Needle-shaped, negatively birefringent MSU crystals |
| Pseudogout | Joint aspiration + XR | USG | Rhomboid, positively birefringent CPPD crystals + chondrocalcinosis on XR |
| Septic arthritis | Joint aspiration (Gram stain URGENT + culture) + blood cultures | MRI (if concern for osteomyelitis) | Positive Gram stain/culture; WBC > 50,000 |
| PAD | ABI (≤ 0.9 diagnostic) | Duplex USG (first-line imaging); CTA; DSA (for intervention) | ABI < 0.9; loss of triphasic waveform |
| Diabetic foot ulcer | TcPO₂ (> 30 mmHg good); probe-to-bone test | XR foot/ankle; MRI (osteomyelitis) | Probe-to-bone +ve = osteomyelitis likely; TcPO₂ < 30 = poor healing |
| Plantar fasciitis | Clinical diagnosis; XR to r/o fracture | USG (fascia > 4 mm); MRI if refractory | Heel spur on XR (incidental; not diagnostic) |
| Achilles rupture | Thompson test (clinical) | USG or MRI | Tendon discontinuity on USG/MRI |
| Stress fracture | XR (may be negative early) | MRI (gold standard for early detection) | Bone marrow oedema on T2/STIR |
| Hallux valgus | AP weight-bearing XR | CT (pre-operative planning) | HV angle > 15°, IM angle > 9° |
| Lisfranc injury | Weight-bearing XR | CT (bony detail); MRI (ligamentous) | Diastasis M1–M2 > 2 mm; fleck sign |
| Charcot arthropathy | XR | MRI or bone scan if XR inconclusive; joint aspiration to rule out DDx | Bony destruction, subluxation, pencil-pointing |
| Tarsal tunnel syndrome | Clinical (Tinel's) + NCS | MRI (cause of compression) | Prolonged distal latency of tibial nerve on NCS |
| Morton's neuroma | Clinical (Mulder's click) + USG | MRI if equivocal | Hypoechoic intermetatarsal mass on USG |
High Yield Summary
Key diagnostic principles for foot/toe pain:
-
Joint aspiration is the MOST IMPORTANT TEST for any acutely swollen joint — send for Gram stain (urgent), culture, crystal microscopy, and cell count. It distinguishes gout (MSU: needle, −ve birefringent) from pseudogout (CPPD: rhomboid, +ve birefringent) from septic arthritis (positive Gram/culture, WBC > 50k).
-
ABI ≤ 0.9 = diagnostic of PAD; < 0.4 = critical ischaemia. ABI > 1.30 = calcified → use TBI instead (especially in DM/ESRD).
-
TcPO₂ > 30 mmHg = adequate wound-healing potential in diabetic foot.
-
Plain XR is first-line for most bony pathology. Always weight-bearing for hallux valgus, pes planus, and Lisfranc.
-
MRI is the problem-solver when XR is negative: stress fracture, early osteomyelitis, soft tissue pathology, subtle Lisfranc injury, Charcot (early).
-
Duplex USG is the first-line imaging for PAD — look for triphasic (normal) → biphasic (single-level) → monophasic (multi-level) waveform changes.
-
Serum urate can be normal during acute gout (12–43%) — defer to 2 weeks post-resolution.
-
Plantar fasciitis is a clinical diagnosis. XR is only to rule out fracture — the heel spur is incidental, not diagnostic.
-
Probe-to-bone test: if probe reaches bone in a diabetic foot ulcer, specificity ~89% for osteomyelitis.
-
NCS useful for: tarsal tunnel syndrome, differentiating axonal vs. demyelinating neuropathy, severity assessment. Not useful for: excluding neuropathy, defining aetiology, CNS pathology.
Active Recall - Diagnosis and Investigations for Foot/Toe Pain
References
[1] Lecture slides: murtagh merge.pdf (p55–57, Foot and ankle pain) [3] Senior notes: Ryan Ho Rheumatology.pdf (p32, Physical Examination and Investigations; p37–38, Gout diagnosis and flare; p42, CPPD workup and diagnosis; p67, Septic arthritis; p136, Cellulitis diagnosis) [4] Senior notes: Ryan Ho Endocrine.pdf (p98–99, Diabetic Foot, Diabetic Neuropathy, Charcot Arthropathy) [5] Senior notes: Ryan Ho Cardiology.pdf (p207, Rest Pain; p214, Assessment of Lower Limb Ischaemia including ABI and Duplex USG) [7] Senior notes: maxim.md (p350, Investigations for PVD including ABPI, Duplex USG, CTA, DSA) [8] Senior notes: maxim.md (p548, Plantar fasciitis investigations; p550, Diabetic foot ulcers investigations and Charcot arthropathy; p539, Pes planus Meary's angle; p538, Hallux valgus XR) [10] Senior notes: Ryan Ho Fundamentals.pdf (p407–410, Approach to joint disease: physical examination, initial investigations, joint fluid analysis) [11] Senior notes: Ryan Ho Diagnostic Radiology.pdf (p13, Plain Film Radiography characteristics and indications) [12] Senior notes: Ryan Ho Neurology.pdf (p38, Electrodiagnostic Studies; p178–179, Approach to peripheral nerve disease)
Management of Foot/Toe Pain
Management of foot/toe pain is condition-specific — there is no "one-size-fits-all" treatment plan. What follows is a master management algorithm, then a systematic, condition-by-condition treatment guide covering conservative, pharmacological, interventional, and surgical modalities. I will explain why each treatment works from first principles.
The overarching logic: Identify and treat the cause, not just the symptom. The algorithm branches by urgency and aetiology.
2. Emergency Management
This is a surgical emergency. Irreversible muscle damage begins at 4–6 hours [6].
Immediate supportive measures [6]:
- Keep the feet dependent — gravity augments perfusion to the ischaemic limb
- O₂ supplementation — maximise tissue oxygenation
- Correction of hypotension — hypotension can precipitate acute thrombosis by low flow (stasis)
Medical treatment [6]:
- Analgesics — opioids often required
- Anticoagulation with IV heparin — ALL patients should be anticoagulated once the diagnosis of acute arterial ischaemia due to emboli or thrombi is made, in the absence of contraindications [6]
- IV heparin bolus followed by continuous heparin infusion
- Aims for APTT 2–2.5× normal
- Rationale: (1) prevents further propagation of thrombus into unaffected vascular beds; (2) inhibits thrombosis distally in arterial and venous systems due to low-flow stasis [6]
Definitive treatment — depends on Rutherford classification and aetiology [5][6]:
| Approach | Modalities | Indications |
|---|---|---|
| Surgical revascularisation | Embolectomy (open); bypass grafting (for long-segment occlusion); ± prophylactic fasciotomy (for compartment syndrome risk) [6] | Immediately threatened extremities (IIb); recent occlusion < 2 weeks; complete ischaemia suggesting embolism [6] |
| Endovascular revascularisation | Intra-arterial thrombolysis; angioplasty and stenting [6] | Viable or marginally threatened extremities (I, IIa); prolonged occlusion > 2 weeks (more likely thrombotic with collaterals); incomplete ischaemia [6] |
| Amputation | Below-knee or above-knee | Non-viable limb (Rutherford III) — completely anaesthetic + paralysed, inaudible arterial AND venous Doppler signals [5] |
Why embolectomy for embolic causes and thrombolysis for thrombotic? Embolectomy (Fogarty catheter — a balloon catheter passed beyond the clot then inflated and pulled back to extract the embolus) works best for discrete, fresh emboli lodged at bifurcation points without surrounding atherosclerotic disease. Thrombolysis (catheter-directed tPA/urokinase infused directly at the thrombus) works better for chronic, organised thrombus superimposed on atherosclerosis, where the thrombus is adherent to the diseased vessel wall and cannot be easily mechanically extracted [5][6].
Below knee [7]: local thrombolysis / bypass
- Complete ischaemia: proceed to LA open embolectomy
- Incomplete ischaemia: obtain pre-op imaging if possible → endovascular treatments
- Non-viable limb: amputation
Post-Revascularisation Complications
After revascularisation, be vigilant for reperfusion injury:
-
Compartment syndrome: prolonged ischaemia → cell lysis → fluid leaks into interstitium → intracompartmental pressure > 30 mmHg → pain out of proportion to clinical signs, tense compartment, numbness in nerve distribution. Pulses can still be present (SBP >> compartmental pressure). Treatment: urgent fasciotomy [5][7].
-
Rhabdomyolysis: reperfusion releases K⁺, H⁺, myoglobin from damaged muscle → arrhythmia, AKI. Management: aggressive hydration, IV bicarbonate (↓ acidosis, ↓ myoglobin cast formation), ± mannitol diuresis, ± dialysis [5][7].
- Joint aspiration — both diagnostic AND therapeutic (decompresses the joint)
- IV antibiotics — empiric Gram-positive cover initially (flucloxacillin / cloxacillin ± gentamicin for Gram-negative cover); adjust based on Gram stain and culture
- In sexually active young adults: cover for N. gonorrhoeae (ceftriaxone)
- In IVDU: cover for P. aeruginosa and MRSA
- Arthroscopic washout / surgical drainage — serial joint aspirations or arthroscopic lavage to remove purulent material and prevent cartilage destruction
- Prompt treatment is critical: bacterial infection can destroy joint cartilage in a few days [3]
- Wet gangrene: emergency requiring surgical debridement or amputation [6]
- Necrotising fasciitis: emergency wide debridement + IV broad-spectrum antibiotics (e.g., meropenem + clindamycin + vancomycin) + ICU care
- Dry gangrene: safe to allow self-amputation after demarcation with precautions against infection [6]
3. Condition-Specific Management
3.1 Peripheral Arterial Disease — Chronic Limb Ischaemia [5][7]
The management approach is dictated by severity: conservative if non-disabling claudication alone; surgery if disabling claudication or critical limb ischaemia [5].
"Claudication won't kill but is associated with ↑↑ risk of stroke and MI (CHD risk equivalent in ATP-III). Should be viewed as a warning sign of CVS disease instead of a condition in itself" [5].
CVS risk factor management to improve survival [5]:
- Risk factor modification: smoking cessation, DM control, HTN control, lipid control
- Lifelong antiplatelets: aspirin (75–325 mg) and/or clopidogrel — secondary prevention of coronary heart disease and stroke [5][7]
- Statin regardless of lipid level — for overall CVS protection [7]
Symptomatic management — 50% of patients improve; < 5% develop critical limb ischaemia [5]:
- Supervised exercise training: walk until pain comes → stop and rest → walk again [5]
- Why does this work? Exercise training increases muscle oxygen extraction efficiency, promotes collateral vessel development, and improves anaerobic metabolism tolerance. The supervised component is key — compliance with unsupervised programs is poor.
- Cilostazol (100 mg BD) — most commonly used drug; PDE3 inhibitor with antiplatelet and vasodilatory effect [5][7]
- Mechanism: inhibits PDE3 → ↑ cAMP in platelets and vascular smooth muscle → platelet aggregation inhibited + vasodilation → improved blood flow
- Contraindicated in CHF (PDE3 inhibitors increase mortality in CHF — learned from milrinone) [7]
- Alternatives: naftidrofuryl (5-HT₂ antagonist: reduces platelet aggregation), pentoxifylline / Trental (PDE inhibitor), prostaglandins [5][7]
Indications [5]:
- Disabling claudication in non-critical ischaemia → at least one trial of conservative treatment unless severe impact on lifestyle → NOT first-line to treat intermittent claudication!
- Limb salvage in critical ischaemia
"Rationale for not going for surgery in IC patients: (1) failed surgery has poorer outcome than no surgery; (2) second surgery is less likely to succeed" [5].
General principles in choosing treatment [5]:
- Treat inflow before outflow disease — treat aortoiliac disease first, then reassess distal disease
- Short stenosis → endovascular; long, complete occlusion → surgical bypass
- Consider venous graft availability (need > 3–4 mm diameter, no varicosities, intact valves or reversed)
- Life expectancy ≤ 2 years → endovascular (better short-term outcome; unlikely to benefit from long-term patency of bypass)
- Rest pain → prefer bypass (durable effect on pain) [5]
TASC II Classification guides the choice [5]:
- Type A: short, focal → excellent result with endovascular therapy
- Type B: still prefer endovascular, can perform surgery
- Type C: better results with open revascularisation but endovascular Tx can be used if high surgical risk
- Type D: usually prefer surgery as primary treatment for low-to-moderate risk patients
| Modality | Description | Best For |
|---|---|---|
| Percutaneous transluminal balloon angioplasty (PTA) ± stenting | Balloon inflated for ~30 seconds → dilates stenosis. Stent placed to maintain patency. Stenting NOT used below the knee [7] | TASC A/B, aortoiliac disease, short-segment occlusion < 10 cm, life expectancy < 2 years [7] |
| Arterial bypass | Autologous vein graft (great saphenous vein preferred) or synthetic graft (Dacron/PTFE). Creates alternative conduit around the occlusion | TASC C/D, failed angioplasty, long-segment occlusion, complete occlusion (no lumen for guidewire) [7] |
| Endarterectomy | Open artery, evacuate atheromatous plaque | Uncommon now except at carotid and femoral bifurcation (profundoplasty) [7] |
| Amputation | Below-knee (preferable — preserves knee for prosthetic fitting) or above-knee | Non-viable limb after failed revascularisation |
Post-PTA/stent: antiplatelet + anticoagulation to prevent stent thrombosis [7].
Specific complications of PTA [7]:
- Arterial dissection / rupture
- Distal embolisation
- Re-stenosis
Prognosis for chronic limb ischaemia [5]:
- Non-critical CLI at 5 years: stable claudication (70–80%), worsening (10–20%), critical CLI (1–2%). CVS: non-fatal MI/stroke (20%), death (15–30%)
- Critical CLI at 1 year: alive with two limbs (50%), amputation (25%), CVS mortality (25%)
Key Exam Point
PAD management is primarily about cardiovascular risk reduction — the biggest killer of claudicants is MI and stroke, not limb loss. Antiplatelets, statins, smoking cessation, and exercise are the cornerstones. Surgery is reserved for disabling symptoms or critical ischaemia.
3.2 Gout [3]
Three first-line options — choice depends on patient comorbidities:
| Agent | Mechanism | Dosing | Key Points |
|---|---|---|---|
| NSAIDs (e.g., naproxen 500 mg BD, indomethacin 50 mg TDS) | COX inhibition → ↓ prostaglandin synthesis → ↓ inflammation and pain | Full dose for 5–7 days, then taper | Avoid in CKD, heart failure, GI bleed history, concomitant anticoagulation. First-line in young, otherwise healthy patients |
| Colchicine | Binds tubulin → inhibits microtubule polymerisation → ↓ neutrophil migration/phagocytosis + ↓ NLRP3 inflammasome activation → ↓ IL-1β release | Low-dose regimen: 0.5 mg TDS (first day), then 0.5 mg BD until resolution | Must be started within 12–36 hours of flare onset for best efficacy. GI side effects (diarrhoea, nausea) dose-dependent. Avoid in severe CKD/hepatic impairment |
| Corticosteroids | Broad anti-inflammatory — suppress NF-κB → ↓ cytokine production | Intra-articular: triamcinolone acetonide 10–40 mg (after aspirating to rule out sepsis) [3]; Oral: prednisolone 30–35 mg/day × 5 days then taper; IM/IV if cannot take oral | Preferred in CKD, elderly, multiple comorbidities. Intra-articular steroid highly effective, resolves attack ≤ 24 hours [3]. Slow taper if chronic gout (shorter intercritical period → ↑ chance of rebound flare) [3] |
Important: Do NOT start or stop urate-lowering therapy (ULT) during an acute flare — changing serum urate acutely can trigger or prolong the flare by causing crystal dissolution or precipitation. If the patient is already on ULT, continue it at the same dose.
Indications for ULT (2020 ACR guidelines):
- ≥ 2 flares per year
- Tophi on clinical examination or imaging
- Urate nephropathy / uric acid nephrolithiasis
- Consider after even first flare if: CKD stage ≥ 3, serum urate > 9 mg/dL, or urolithiasis
Target: serum urate < 6 mg/dL (< 0.36 mmol/L); < 5 mg/dL if tophaceous gout (to dissolve existing deposits).
| Agent | Mechanism | Dosing | Key Points |
|---|---|---|---|
| Allopurinol | Xanthine oxidase inhibitor → ↓ uric acid production ("allo" = other + "purinol" = purine metabolism) | Start low (100 mg/day; 50 mg in CKD), titrate by 100 mg every 2–4 weeks to target | First-line ULT. Rare but serious: allopurinol hypersensitivity syndrome (AHS) — SJS/TEN, DRESS. HLA-B5801 screening MANDATORY before starting in Southeast Asian/Chinese populations* (prevalence ~6–8% in HK Chinese) |
| Febuxostat | Non-purine selective xanthine oxidase inhibitor | 40–80 mg daily | Alternative if allopurinol intolerant/contraindicated. Concerns about ↑ CV mortality (CARES trial) — use with caution in CVD |
| Probenecid | Uricosuric — blocks URAT1 transporter in proximal tubule → ↑ renal urate excretion | 500 mg BD | Contraindicated in CKD (eGFR < 30), nephrolithiasis. Requires adequate urine output and alkalinisation |
| Pegloticase | Recombinant PEG-uricase — converts uric acid to allantoin (which is more soluble) | IV infusion every 2 weeks | Reserved for severe refractory tophaceous gout. Risk of anaphylaxis, infusion reactions |
Flare prophylaxis during ULT initiation: Low-dose colchicine (0.5 mg daily) or low-dose NSAID for ≥ 3–6 months (or 6 months after achieving target urate). Why? Starting ULT changes serum urate levels → crystal dissolution from cartilage surface → "naked" crystals shed into joint space → inflammatory response → paradoxical flare.
HLA-B*5801 Screening
In Hong Kong Chinese, HLA-B5801 prevalence is approximately 6–8%*. Allopurinol hypersensitivity syndrome is strongly associated with this allele and can be fatal (SJS/TEN). Screening is MANDATORY before starting allopurinol in all patients of Southeast Asian, Chinese, Korean, Thai, and African American descent. If positive → use febuxostat instead.
| Setting | Treatment | Notes |
|---|---|---|
| Acute pseudogout (1–2 joints) | Thorough joint aspiration + intra-articular glucocorticoid injection [3]. Regimen: triamcinolone acetonide (1 mL, 40 mg) mixed with 1–2 mL 1% lidocaine for large joints [3]. Effect: usually provides relief of pain/swelling ≤ 8–24 hours [3] | Must rule out septic arthritis before steroid injection [3]. Also: ice pack, immobilisation, joint rest for 48–72 hours |
| Acute pseudogout ( > 2 joints) | Systemic anti-inflammatory drug (NSAIDs, colchicine, or oral steroids) [3] | Same agents as gout flare |
| Chronic CPPD arthropathy | Low-dose colchicine; NSAIDs as needed; methotrexate or hydroxychloroquine in refractory cases | No therapy dissolves existing CPPD crystals |
| Underlying cause | Correction of underlying cause, e.g., hyperparathyroidism [3]; screen for haemochromatosis, hypomagnesaemia |
There is no equivalent of allopurinol for CPPD — we cannot dissolve or prevent CPPD crystal formation pharmacologically. Management is entirely symptomatic and directed at treating the underlying metabolic abnormality.
A stepwise approach over 6–12 months — the vast majority resolve with conservative treatment.
| Step | Treatment | Mechanism / Rationale |
|---|---|---|
| 1. Non-operative (first-line) | Pain control (NSAIDs, paracetamol) [8] | Reduce inflammation and pain |
| Footwear adjustment — supportive shoes with arch support, cushioned heel [8] | Offloads the calcaneal origin; reduces tensile stress on the fascia | |
| Physiotherapy — calf stretching, plantar fascia-specific stretching, eccentric exercises [8] | Stretching the gastrocnemius-soleus complex reduces tension transmitted to the fascia via the Achilles-calcaneal-plantar system (the gastrocnemius and plantar fascia are functionally linked through the calcaneus) | |
| Night splint (keeps foot in dorsiflexion overnight) | Prevents fascia from contracting overnight → reduces first-step morning pain | |
| 2. If refractory (3–6 months) | Extracorporeal shockwave therapy (ESWT) [8] | Delivers focused acoustic energy → stimulates neovascularisation and tissue remodelling in the degenerate fascia; also provides analgesic effect through hyperstimulation of nociceptors |
| Corticosteroid injection (ultrasound-guided) [8] | Potent local anti-inflammatory. Risks: plantar fascia rupture (weakens collagen), fat pad atrophy. Limit to 1–3 injections | |
| 3. Operative (last resort) | Plantar fasciotomy — partial release of the plantar fascia from the calcaneus [8] | Relieves tension at the origin. Risk: destabilisation of the medial longitudinal arch |
3.5 Achilles Tendinopathy and Rupture [8]
- Avoid precipitating exercise [8] — relative rest, activity modification
- NSAIDs — short course for pain; avoid long-term (may impair tendon healing)
- Physiotherapy — eccentric exercises (Alfredson protocol: heavy-load eccentric calf exercises — slowly lowering the heel over the edge of a step). Why eccentric? Eccentric loading preferentially stimulates collagen remodelling and tenocyte activity in the degenerative tendon [8]
- GTN patches (topical nitric oxide donors) — stimulate collagen synthesis; evidence mixed
- Avoid corticosteroid injection into or around the Achilles — significant risk of tendon rupture
| Scenario | Management | Details |
|---|---|---|
| Early presentation ( < 2 weeks) | Plaster immobilisation in full equinus (foot plantarflexion + toe extension) × 2 weeks → semi-equinus × 4 weeks → neutral position × 4 weeks [8] | Non-operative functional rehabilitation; similar outcomes to surgery in some studies if applied early and patient is compliant |
| Late presentation ( > 2 weeks) / Relatively active patient | End-to-end tendon repair ± FHL graft (if no pre-existing tendinopathy) [8]; Achilles tendon reconstruction (if tendinopathy) [8] | Surgical repair indicated for late or active patients because the tendon ends retract and scar tissue fills the gap, preventing apposition |
Why can active ankle plantarflexion still occur after Achilles rupture? Because other muscles — tibialis posterior, peroneus longus and brevis — also contribute to plantarflexion, though much weaker than the gastrocnemius-soleus complex [8]. This is why a missed rupture is possible if only active motion is tested without the Thompson test.
| Approach | Details | Indications |
|---|---|---|
| Conservative | Footwear: wide and deep toe boxes, avoid high heels and narrow shoes; orthosis for flatfoot; physiotherapy: intrinsic muscle strengthening [8] | Mild symptoms, patient not wanting surgery |
| Surgical (only EBM recommendation) | Depends on severity and whether the joint is arthritic [8] | Significant pain, functional limitation, progressive deformity |
Surgical options [8]:
| Joint Status | Procedure | Description |
|---|---|---|
| Non-arthritic joint | Chevron osteotomy (mild HV) | V-shaped osteotomy of distal 1st MT → translate the metatarsal head laterally |
| Scarf osteotomy (moderate/severe HV) | Z-shaped osteotomy of 1st MT shaft → allows multiplanar correction | |
| Soft tissue rebalancing (e.g., McBride) | Release of tight lateral structures (adductor hallucis) + medial capsule plication | |
| Arthritic joint | Arthrodesis (e.g., Lapidus procedure) — 1st TMT joint fusion [8] | Fuses the hypermobile joint — addresses the root cause in many cases |
| Keller's procedure (excision arthroplasty + hemiphalangectomy) [8] | Removes the proximal portion of the proximal phalanx — shortens the toe, suitable for elderly/low-demand patients |
Complications of hallux valgus surgery [8]: avascular necrosis, non-union, displacement, reduced ROM.
- Identify and treat / refer early [8]
- Insole: medial heel wedge [8] — supports the medial longitudinal arch by tilting the hindfoot out of valgus
- Tibialis posterior tendon dysfunction: activity modification, supportive footwear, physiotherapy → if failed, surgical options include tendon transfer (FDL transfer), calcaneal osteotomy, subtalar fusion
"Multidisciplinary approach (refer podiatry) for those at high risk or with Hx of foot ulcers" [4].
| Component | Management |
|---|---|
| Prevention | Annual comprehensive foot examination including inspection + palpation of pulses [4]; examine at every visit for insensate feet, foot deformities, and ulcers [4]; refer vascular surgery for patients with significant claudication or positive ABI [4]; general foot self-care for all DM patients [4] |
| Neuropathic component | Customised insole — offloads pressure from high-risk areas (MT heads, bony prominences) [8]; total contact casting for neuropathic ulcers |
| Vascular component | Angioplasty if significant PAD contributing to ischaemia [8]; optimise cardiovascular risk factors |
| Glycaemic control | Optimise glycaemic control as mainstay for neuropathy progression [4]; gabapentinoids (gabapentin/pregabalin) and antidepressants (amitriptyline) for neuropathic pain [4] |
| Infection | Empiric antibiotics for cellulitis (amoxicillin + cloxacillin); long-course antibiotics (6–8 weeks) for osteomyelitis; surgical debridement of necrotic tissue [8] |
| Surgical | Debridement, below-knee amputation (if non-viable) [8] |
Charcot Arthropathy [4][8]
- Short-term immobilisation (3–6 months): proven to ↓ long-term joint damage and progression [4] — total contact cast or removable cast walker to offload the affected foot
- Walking aid to offload foot [8]
- Consider antiresorptive agents (bisphosphonates, calcitonin) as adjunct (evidence uncertain) [4]
- Consider orthopaedic referral for surgical correction in severe cases [4]
- Surgical correction best avoided: high failure rate [8] — only when conservative management fails and the deformity causes recurrent ulceration
- Conservative: RICE (Rest, Ice, Compression, Elevation), then early mobilisation [8]
- Ankle instability: physiotherapy for peroneal muscle strengthening, braces to prevent recurrent sprains [8]
- Surgery for ankle instability: if pain and instability despite conservative management [8]
Ottawa Ankle Rules determine need for XR [8]: bone tenderness at posterior malleoli/tips OR inability to bear weight for 4 steps → XR indicated.
| Setting | Management |
|---|---|
| Non-operative | Non-displaced fracture, Weber A, Weber B without talar shift: closed reduction, below-knee back slab, repeat neurovascular exam + XR [8] |
| Operative | Bimalleolar/trimalleolar fracture, Weber B with talar shift, Weber C, open fracture: ORIF ± syndesmotic screw / tightrope fixation [8] |
- NSAIDs or COX-2 inhibitor as first line [3] — ~70–80% report substantial symptom relief
- Anti-TNF or anti-IL-17A as second line if persistent high disease activity despite NSAIDs [3]
- Local glucocorticoid injections for enthesitis and dactylitis [3]
- DMARDs (e.g., sulphasalazine) may be useful in persistent peripheral arthritis [3]
- General measures: patient education, stretching exercise/physiotherapy, smoking cessation [3]
| Condition | Management |
|---|---|
| Plantar warts | Conservative: spontaneous resolution in majority but may take years [9]. Destructive: topical salicylic acid (exfoliates affected epidermis, stimulates local immunity); cryotherapy with liquid nitrogen (risk: scarring, pain); surgical removal (shave, curettage, paring) [9]. Refractory: intralesional bleomycin, imiquimod, pulsed laser |
| Corns/calluses | Paring of hyperkeratotic tissue; offloading with padding/orthotics; footwear modification; salicylic acid plasters |
| Ingrown toenail | Mild: conservative (proper cutting technique, cotton wool/dental floss under nail edge); moderate/recurrent: partial nail avulsion + phenolisation (chemical matrixectomy — phenol destroys the germinal matrix to prevent regrowth of the offending nail edge); severe/infected: antibiotics + surgical excision (Zadik procedure — total nail bed ablation if recurrent) |
- Conservative: wider footwear, metatarsal pad (placed proximal to the affected interspace to splay the MT heads and decompress the nerve), activity modification, NSAIDs
- Injection: ultrasound-guided corticosteroid injection into the intermetatarsal space — provides temporary relief in ~50%
- Surgical: neurectomy (excision of the neuroma) if failed conservative treatment > 3–6 months. Risk: permanent numbness in the affected web space (expected — you are removing the nerve)
- Low-risk stress fractures (2nd/3rd MT shaft): relative rest, protected weight-bearing with stiff-soled shoe/walking boot for 4–6 weeks; graduated return to activity
- High-risk stress fractures (navicular, 5th MT Jones fracture, sesamoid): non-weight-bearing cast for 6–8 weeks; surgical fixation (percutaneous screw) if delayed union or complete fracture
Why is the navicular stress fracture high-risk? The central portion of the navicular has a relatively avascular zone (blood supply enters from the periphery), analogous to the waist of the scaphoid. Fractures through this zone are prone to non-union and avascular necrosis if not aggressively immobilised.
| Condition | Conservative | Pharmacological | Interventional / Surgical |
|---|---|---|---|
| PAD — claudication | Exercise, RF modification | Aspirin, statin, cilostazol | PTA ± stent, bypass (if disabling) |
| PAD — critical ischaemia | Keep leg dependent, O₂ | Heparin, opioids | Urgent PTA/bypass or amputation |
| Acute gout | Rest, ice | NSAIDs / colchicine / steroids | IA steroid injection |
| Chronic gout | Diet, lifestyle | Allopurinol (screen HLA-B*5801!) / febuxostat | Tophus excision (rare) |
| Plantar fasciitis | Footwear, PT, stretching, night splint | NSAIDs; steroid injection if refractory | ESWT; plantar fasciotomy (last resort) |
| Achilles tendinopathy | Relative rest, eccentric exercises | NSAIDs (short course) | Avoid steroid injection |
| Achilles rupture | Equinus casting ( < 2 weeks) | — | Surgical repair (late/ active) |
| Hallux valgus | Wide shoes, orthotics, PT | — | Osteotomy (Chevron/Scarf), Keller's, Lapidus |
| Diabetic foot | Insoles, education, multidisciplinary | Glycaemic control, gabapentinoids | Angioplasty, debridement, amputation |
| Charcot arthropathy | Immobilisation 3–6 months, walking aid | Bisphosphonates (uncertain) | Surgery avoided; referral if severe |
| Ankle sprain | RICE, early mobilisation, PT | NSAIDs | Brostrom-Gould (if instability) |
| Morton's neuroma | Wider shoes, metatarsal pad | NSAIDs; steroid injection | Neurectomy |
| Ingrown toenail | Proper nail care | Antibiotics if infected | Partial nail avulsion + phenolisation |
High Yield Summary
Emergency management priorities:
- Acute limb ischaemia: IV heparin immediately → assess viability → embolectomy / thrombolysis / amputation. Watch for compartment syndrome and rhabdomyolysis post-revascularisation.
- Septic arthritis: aspirate → IV antibiotics → washout. Cartilage destroyed in days if untreated.
- Wet gangrene: emergency debridement/amputation. Dry gangrene can self-amputate.
PAD management:
- Conservative first: smoking cessation, supervised exercise, aspirin, statin, cilostazol (C/I in CHF).
- Surgery only for disabling claudication or critical ischaemia. TASC A/B → endovascular; TASC C/D → surgery. Treat inflow before outflow.
Gout management:
- Acute: NSAIDs / colchicine / steroids (choose based on comorbidities).
- Long-term ULT: allopurinol first-line (HLA-B*5801 screening mandatory in HK Chinese!), target urate < 6 mg/dL. Flare prophylaxis with low-dose colchicine × 3–6 months.
Plantar fasciitis: stepwise — footwear + PT + stretching → ESWT / steroid injection → fasciotomy. Clinical diagnosis; heel spur is incidental.
Achilles: eccentric exercises for tendinopathy (NO steroids!). Rupture < 2 weeks → equinus cast; > 2 weeks/active → surgical repair.
Diabetic foot: multidisciplinary — prevention (annual foot exam, education), insoles (neuropathic), angioplasty (vascular), debridement/amputation (surgical). Charcot: immobilise 3–6 months.
Hallux valgus surgery: Chevron (mild), Scarf (moderate/severe), Lapidus/Keller's (arthritic).
Active Recall - Management of Foot/Toe Pain
References
[1] Lecture slides: murtagh merge.pdf (p55–57, Foot and ankle pain) [3] Senior notes: Ryan Ho Rheumatology.pdf (p23, Ankle and Foot examination; p38, Acute gout management; p42, CPPD management; p62, SpA management; p67, Septic arthritis) [4] Senior notes: Ryan Ho Endocrine.pdf (p97–99, Diabetic Nephropathy, Diabetic Neuropathy, Diabetic Foot, Charcot Arthropathy management) [5] Senior notes: Ryan Ho Cardiology.pdf (p207, Rest Pain; p215–216, Assessment and Management of Lower Limb Ischaemia; p238, CVI Management) [6] Senior notes: felixlai.md (p923–924, Acute arterial insufficiency supportive and medical treatment, surgical modalities; p932, Gangrene; p947–948, CVI treatment) [7] Senior notes: maxim.md (p354, PAD conservative and definitive management; p361, Below-knee management, complications including compartment syndrome and rhabdomyolysis) [8] Senior notes: maxim.md (p541–542, Ankle sprain and fracture management; p547–548, Achilles tendinopathy/rupture and Plantar fasciitis management; p538–540, Hallux valgus, Pes planus, Pes cavus management; p550, Diabetic foot ulcers and Charcot management) [9] Senior notes: Ryan Ho Rheumatology.pdf (p138, Viral warts management)
Complications of Foot/Toe Pain Conditions
Complications are best understood not as random events but as the natural consequences of the underlying pathophysiology when it progresses unchecked or when treatments themselves cause harm. I will systematically cover complications arising from the major conditions that cause foot/toe pain, and then complications of the treatments themselves (surgical, pharmacological, interventional). For each complication I will explain why it occurs — the mechanism.
1. Complications of Peripheral Arterial Disease and Limb Ischaemia
| Complication | Mechanism | Clinical Significance |
|---|---|---|
| Progression from claudication to critical limb ischaemia | Progressive atherosclerotic narrowing → collaterals eventually become insufficient even for resting metabolic demand → rest pain → tissue necrosis. At 5 years: stable claudication 70–80%, worsening 10–20%, critical CLI 1–2% [5] | Non-critical ischaemia is not primarily a limb problem — it is a CVS risk marker. The bigger killer is MI and stroke: non-fatal MI/stroke 20%, death 15–30% at 5 years [5] |
| Gangrene (dry and wet) | Dry gangrene: gradual arterial occlusion → coagulative necrosis of tissue without infection → hard, dry, shrunken, clear line of demarcation. Wet gangrene: superimposed bacterial infection on ischaemic tissue → liquefactive necrosis → soft, moist, swollen, no clear demarcation, surgical emergency [6] | Dry gangrene can be observed; wet gangrene demands emergency debridement/amputation because the infection can spread systemically (sepsis) and proximally |
| Ulceration | Chronic ischaemia → skin cannot repair even minor trauma → breakdown at pressure areas (heel, MT heads, between toes, tip of toes [5]). Unlike venous ulcers (medial malleolus), arterial ulcers are distal, well-defined, "punched out," painful, with a pale or necrotic base | The inability to heal drives chronic pain and infection risk |
| Cardiovascular events (MI, stroke) | PAD is a CHD risk equivalent (ATP-III) [5]. Atherosclerosis is a systemic disease — if it affects the leg arteries, the coronary and cerebral arteries are almost certainly affected too | Critical CLI at 1 year: alive with two limbs 50%, amputation 25%, CVS mortality 25% [5]. This is the single most important prognostic point |
1.2 Complications of Ischaemia Itself [5][6][7]
This deserves a deep dive because it is a must-not-miss surgical emergency, commonly tested.
Mechanism: Prolonged ischaemia (≥ 6 hours) + delayed revascularisation → fluid leaks out via damaged cell membranes → oedema within the non-distensible fascial compartment → intracompartmental pressure rises → secondary ischaemia when pressure ≥ 30 mmHg or within 30 mmHg of diastolic BP [5].
This creates a vicious cycle: ischaemia → cell damage → swelling → more ischaemia → more swelling.
Site: commonly calf, especially the anterior tibial compartment [5]. Involvement of the posterior compartment is the most functionally devastating because it contains the tibial nerve and the deep flexors — damage leads to permanent foot deformity and sensory loss [6].
- Pain out of proportion to the clinical situation (earliest symptom [5])
- Pain with passive stretch (most sensitive sign [5]) — passively dorsiflexing the toes stretches the muscles within the compartment → excruciating pain
- Numbness in the distribution of nerves running within the compartment — numbness in the web space between first and second toes suggests compression of the deep peroneal nerve in the anterior compartment [6]
- Tense compartment on palpation
- Pulses can be present because SBP >> intracompartmental pressure — a palpable pulse does NOT rule out compartment syndrome [7]
Management: Emergent fasciotomy → lay open for oedema to resolve, then close after a few days [5]. Consider prophylactic fasciotomy in OT if drastic ischaemia [5]. Check compartment pressure ( < 20 mmHg of diastolic BP) if in doubt [5].
Classic Exam Trap
The presence of peripheral pulses does NOT exclude compartment syndrome. Compartment syndrome is a microvascular phenomenon — the pressure required to occlude the large arteries (systolic BP) is far higher than the pressure causing capillary collapse and tissue ischaemia (≥ 30 mmHg). By the time pulses are lost, irreversible damage has long since occurred. Always diagnose by clinical signs (pain out of proportion, pain with passive stretch) and compartment pressure measurement if in doubt [5][7].
Mechanism: Reperfusion → release of K⁺, lactic acid, myoglobin, and CK from damaged muscle cells into the systemic circulation [5][6].
| Consequence | Why |
|---|---|
| Hyperkalaemia → cardiac arrhythmia | K⁺ released from lysed myocytes; can cause fatal ventricular fibrillation. ECG changes: peaked T waves → widened QRS → sine wave → VF |
| Myoglobin → acute kidney injury (AKI) | Myoglobin is freely filtered by the glomerulus; in acidic urine, it precipitates as casts in the renal tubules → acute tubular necrosis (ATN) [6]. Also, myoglobin generates free radicals that are directly nephrotoxic |
| Lactic acidosis | Anaerobic metabolism during ischaemia produces lactate; reperfusion washes this into the systemic circulation |
| ARDS | Systemic inflammatory response from reperfusion injury → lung capillary leak [5] |
Risk factors: poor background renal function [5]
- Aggressive hydration (target UO > 200–300 mL/hour) — dilutes myoglobin in the tubules, maintains renal perfusion
- IV bicarbonate — ↓ acidosis, ↓ myoglobin cast formation (alkalinising the urine prevents myoglobin precipitation in tubules) [5]
- Mannitol diuresis — osmotic diuretic forces high urine flow, flushing myoglobin from tubules [7]
- Dialysis if refractory AKI or hyperkalaemia [5]
- Post-op monitoring: BP/pulse, urine output, APTT, RFT, cardiac monitor [7]
Mechanism: Formation of oxygen-free radicals upon re-introduction of oxygenated blood to ischaemic tissue → direct oxidative tissue damage + WBC accumulation and sequestration in microcirculation → paradoxically prolongs the ischaemic interval because impaired nutrient flow persists despite restoration of axial blood flow [6].
This is why revascularisation, while life-saving, is not without harm — it can actually worsen tissue damage in the short term.
This is the most devastating complication of diabetes affecting the foot and the leading cause of non-traumatic lower limb amputation worldwide [4].
| Complication | Mechanism |
|---|---|
| Foot ulcers | 25% lifetime risk, annual risk 2%/year [4]. RFs: previous foot ulceration (most important), neuropathy (80%), foot deformity, concomitant vascular disease [4]. Neuropathy → loss of protective sensation → unrecognised repetitive trauma → skin breakdown at pressure points (MT heads, heel, toes). Motor neuropathy → intrinsic muscle wasting → claw toes → altered biomechanics → abnormal pressure distribution. Autonomic neuropathy → dry skin (loss of sweating) → cracking → portal of entry for infection |
| Diabetic foot infections (cellulitis, osteomyelitis) | Ulcer provides a portal of entry; hyperglycaemia impairs neutrophil function (chemotaxis, phagocytosis, oxidative burst are all blunted) → poor immune defence → polymicrobial infection. Osteomyelitis occurs when infection spreads from soft tissue to bone through a deep ulcer (probe-to-bone test positive) |
| Charcot arthropathy | Lack of proprioception → ligament laxity → joint instability + deformity → prone to damage by minor trauma → vasomotor changes due to autonomic neuropathy lead to exaggerated local inflammatory response → progressive bony destruction [4]. Complications of Charcot: stress fractures, subluxation/dislocations [4], collapse of midfoot arch (rocker-bottom deformity), pressure ulcerations over bony prominences |
| Amputation | The final common pathway when ischaemia + infection + neuropathy combine. BKA (most common type): 90% will walk again; AKA: 50% will walk again [6]. Unilateral BKA increases energy expenditure by 40%; bilateral BKA by 60–70% [6] |
| Autonomic complications | Cardiovascular: resting tachycardia, orthostatic hypotension, exercise intolerance; sudomotor: distal hypohidrosis → dry cracking skin (further ulceration risk); GI: gastroparesis; genitourinary: bladder dysfunction, erectile dysfunction [4] |
The diabetic foot cascade: Neuropathy → deformity + loss of sensation → unrecognised trauma → ulcer → infection → osteomyelitis → amputation. Every step in this cascade is potentially preventable with proper screening (annual foot examination with monofilament testing), education, footwear, and glycaemic control [4].
| Complication | Mechanism |
|---|---|
| Chronic tophaceous gout | Persistent hyperuricaemia → continued MSU crystal deposition → gouty tophi (collections of solid MSU crystals with surrounding inflammation and soft tissue destruction) at extensor surfaces, fingers, elbows, Achilles tendons, helix of ear [3]. Complications of tophi: ulceration with discharging whitish gritty material, infection, inflammation (erythema and pus discharge without infection → may mimic dactylitis) [3] |
| Progressive joint destruction | Chronic crystal-induced inflammation → pannus-like tissue → erosion of cartilage and bone. XR: "rat-bite" erosions with overhanging edges |
| Renal manifestations | Urate stones (uric acid nephrolithiasis — uric acid is poorly soluble in acidic urine → stones form in concentrated, acidic urine); uric acid nephropathy (crystal deposition in renal interstitium → chronic tubulointerstitial nephritis) [3] |
| Increasing flare frequency | In untreated patients, 2nd flare occurs ≤ 1 year (62%), ≤ 2 years (78%), ≤ 10 years (93%) [3]. Flares become progressively shorter intercritical period, increasingly prolonged, disabling, polyarticular and may be associated with fever [3] |
| Secondary infection of tophi | Tophi that ulcerate through the skin create a portal of entry for bacteria → secondary septic arthritis on a background of crystal arthropathy — a dangerous combination that can be difficult to diagnose (since the joint is already inflamed) |
Disease complications (from the deformity itself):
- Transfer metatarsalgia (2nd and 3rd MTPJ overload) — as the 1st ray becomes insufficient due to the deformity, load transfers to the lesser MTPJs → pain under 2nd/3rd MT heads [8]
- Bunionette (5th MTPJ) — widening of the forefoot leads to prominence of the 5th MT head → friction and pain
- OA of the 1st MTPJ — malalignment accelerates cartilage wear
- Plantar callosities — altered biomechanics → abnormal pressure distribution → skin thickening
Surgical complications [8]:
- Avascular necrosis — osteotomy disrupts blood supply to the metatarsal head (especially distal osteotomies like Chevron)
- Non-union — failure of the osteotomy to heal (risk factors: smoking, inadequate fixation)
- Displacement — loss of fixation → recurrence of deformity
- Reduced ROM — excessive scar tissue or overtightening of the capsule → stiffness
- Tenosynovitis of calcaneonavicular ligament (spring ligament) — the collapsed arch places excessive strain on this ligament → permanent elongation → rupture → worsening arch collapse → secondary arthritis (a vicious cycle) [8]
- Progressive hindfoot valgus → lateral ankle impingement
- Secondary metatarsalgia from altered biomechanics
- If from tibialis posterior tendon dysfunction: tendon eventually ruptures → rigid flat foot deformity that is no longer correctable conservatively
| Complication | Mechanism |
|---|---|
| Chronic tendinosis → complete rupture | Untreated tendinopathy → progressive degeneration → threshold for rupture is lowered → rupture can occur with minimal force. Active ankle plantarflexion still possible after rupture (tibialis posterior, peroneus longus and brevis compensate), which is why rupture can be missed if only active ROM is tested without the Thompson test [8] |
| Missed rupture | If not diagnosed acutely → tendon ends retract → gap fills with scar tissue → chronic weakness, inability to push off, altered gait → compensatory overload of other structures (plantar fasciitis, knee pain). Late surgical repair is more complex and outcomes are inferior |
| Post-surgical complications | Wound healing problems (the skin over the Achilles has poor vascularity), sural nerve injury, re-rupture (~2–5% after surgical repair), deep vein thrombosis (from immobilisation) |
| Complication | Details |
|---|---|
| Chronic ankle instability | Repeated lateral ankle sprains → attenuated ATFL/CFL → mechanical instability + functional instability (proprioceptive deficit). Leads to recurrent sprains, OA of the ankle joint |
| Osteochondral lesion of the talus | Medial ankle joint pain after inversion injury → interruption of cartilage + underlying bone at the medial talar dome. Can cause chronic pain, catching, effusion. Diagnosed by MRI; may require arthroscopic debridement + microfracture |
| Post-traumatic OA | Ankle fracture (especially involving the articular surface) → incongruent joint → accelerated cartilage wear → OA. Risk is highest with malreduced fractures or missed Lisfranc injuries |
| Nerve injury after surgery | Saphenous nerve (at mid-thigh and mid-leg): sensory to medial leg and medial foot. Sural nerve (at lateral leg): sensory to posterior leg and lateral foot [7] |
| Syndesmotic injury (high ankle sprain) | Disruption of the tibiofibular syndesmosis → widening of the mortise → ankle instability → requires fixation (syndesmotic screw or tightrope) |
Indications for amputation (mnemonic: 3D) [7]:
- Dead: ischaemia and unsalvageable
- Damage: trauma / burns
- Danger: gangrene / necrotising fasciitis / osteomyelitis / ascending sepsis / malignancy
Principles [6]:
- Remove all infected tissues
- Ensure adequacy of blood supply to heal the amputation
- Preserve as much length of extremity as possible — improves rehabilitation opportunity
| Timing | Complication | Mechanism |
|---|---|---|
| Early | Bleeding and haematoma formation | Surgical vascular injury; coagulopathy |
| Wound infection | Contamination; poor perfusion of stump (especially in vascular disease) | |
| Phantom limb pain | Reorganisation of somatosensory cortex — the cortical representation of the amputated limb persists and generates spontaneous pain signals. Also, neuroma formation at the severed nerve endings sends abnormal afferent signals. Affects up to 80% of amputees. Treatment: gabapentinoids, mirror therapy, TENS | |
| Skin necrosis | Secondary to poor perfusion of stump [6] — if the amputation level was too distal for the available blood supply | |
| Late | Stump ulceration | Pressure on poorly vascularised/poorly padded stump |
| Stump neuroma | Cut nerve endings attempt to regenerate → form a disorganised ball of axonal sprouts (neuroma) → exquisitely tender on pressure | |
| Osteomyelitis | Infection reaching the exposed bone end, especially if wound healing was compromised | |
| Osteophyte formation in underlying bone | Periosteal reaction at the bone end → bony spurs that can cause socket discomfort | |
| Fixed flexion deformity | Prolonged immobilisation/improper positioning → contracture (especially hip flexion in AKA, knee flexion in BKA) → impairs prosthetic fitting | |
| Difficult mobilisation | Deconditioning, energy expenditure increase (40% BKA unilateral, 60–70% bilateral BKA, 100% AKA unilateral) [6], psychological factors, prosthetic issues |
Phantom Limb Pain — Why Does It Happen?
After amputation, the brain's somatosensory cortex still has the "map" of the lost limb. Neurons that previously received input from the amputated foot now receive input from adjacent cortical regions (cortical remapping — Ramachandran). This mismatch generates pain in a limb that no longer exists. Additionally, the severed peripheral nerve endings form neuromas that fire spontaneously, sending nociceptive signals to the brain that are interpreted as originating from the absent limb. Mirror therapy (where the patient watches the reflection of their intact limb being moved, creating the visual illusion that the amputated limb is moving normally) can "retrain" the cortex and reduce phantom pain.
9. Complications of Specific Treatments
| Complication | Mechanism |
|---|---|
| Arterial dissection / rupture | Balloon inflation or guidewire manipulation can tear the intima or even the full vessel wall |
| Distal embolisation | Balloon inflation can dislodge atherosclerotic debris → travels distally → occludes smaller arteries → "trash foot" / blue toe syndrome |
| Re-stenosis | Neointimal hyperplasia — smooth muscle cells proliferate in response to endothelial injury from the balloon/stent → progressive re-narrowing (typically 6–12 months). Drug-eluting stents reduce this |
| Contrast nephropathy | Iodinated contrast is directly toxic to renal tubular cells and causes renal vasoconstriction → AKI. Risk: pre-existing CKD, dehydration, diabetes |
| Access site complications | Haematoma, pseudoaneurysm, AV fistula at the femoral puncture site |
- Stroke and haemorrhage: patients treated with endovascular procedures (thrombolysis) are associated with a higher risk of stroke and major haemorrhage including GI bleeding and haematoma at vascular puncture site [6]
- Contraindications: previous stroke/TIA, recent GI bleed, bleeding tendency, pregnancy [7]
| Complication | Mechanism |
|---|---|
| Plantar fascia rupture | Corticosteroids inhibit collagen synthesis → weakens the fascia → risk of rupture, especially with repeated injections |
| Fat pad atrophy | Steroid diffuses into the calcaneal fat pad → adipocyte atrophy → loss of shock absorption → chronic heel pain |
| Infection | Any injection carries a small risk of introducing bacteria; must use strict aseptic technique and rule out septic arthritis before injecting |
| Skin depigmentation / subcutaneous atrophy | Local steroid effect on melanocytes and subcutaneous tissue |
- Allopurinol hypersensitivity syndrome (AHS): severe drug reaction manifesting as SJS/TEN, DRESS (Drug Reaction with Eosinophilia and Systemic Symptoms), acute hepatitis, interstitial nephritis
- Strongly associated with HLA-B5801* — prevalence ~6–8% in HK Chinese
- Mortality rate of AHS: 20–25%
- Prevention: HLA-B5801 screening mandatory before starting allopurinol in at-risk populations*; start low, go slow (100 mg/day, titrate gradually)
| Complication | Mechanism |
|---|---|
| GI ulceration/bleeding | COX-1 inhibition → ↓ protective prostaglandins in gastric mucosa → mucosal injury. Risk: elderly, concurrent anticoagulation, H. pylori, previous GI bleed |
| Renal impairment | COX inhibition → ↓ prostaglandin-mediated afferent arteriolar vasodilation → ↓ GFR. Risk: CKD, dehydration, heart failure, concurrent ACEi/ARB |
| Cardiovascular events | COX-2 selective inhibition → imbalance between thromboxane A₂ (pro-thrombotic) and prostacyclin (anti-thrombotic) → ↑ thrombotic risk |
| Hypertension | Sodium and water retention from renal prostaglandin inhibition |
- Fluoroquinolones (ciprofloxacin, levofloxacin, moxifloxacin) can cause Achilles tendinopathy and rupture [1]
- Mechanism: fluoroquinolones directly impair tenocyte proliferation and collagen synthesis; also ↑ matrix metalloproteinase (MMP) activity → tendon degradation
- Risk factors: age > 60, concurrent corticosteroids, CKD, prior tendon disorders
- This is an important drug-related masquerade for foot/toe pain — always check the drug history [1]
| Complication | Mechanism |
|---|---|
| Trophic changes | Denervation of skin → disuse atrophy, hair loss, brittle nails, trophic ulcers, Charcot joints [12] — the loss of trophic factors normally supplied by intact nerve fibres leads to tissue degeneration |
| Skeletal deformity | Motor neuropathy → muscle imbalance → claw toes, pes cavus, kyphoscoliosis [12] |
| Falls and injuries | Loss of proprioception + motor weakness → gait instability → falls → fractures |
| Neuropathic pain | Damaged nerve fibres fire spontaneously → chronic burning, shooting, electric-shock pain that is often refractory to conventional analgesics and requires gabapentinoids or amitriptyline [4] |
| Complication | Mechanism |
|---|---|
| Forefoot destruction | Symmetric MTPJ synovitis → pannus → erosion of cartilage and bone → hallux valgus, clawing/crowding of toes, subluxation of MT heads through plantar skin [3][10] → "walking on pebbles" |
| Flattening of arches | Flattening of transverse/longitudinal plantar arches may occur in arthritic conditions of foot (e.g., RA) [10] |
| Rheumatoid nodules on Achilles tendon | Subcutaneous nodules at pressure points → risk of Achilles rupture if the tendon is weakened |
| Secondary OA | Chronic joint damage → degenerative changes superimposed on inflammatory destruction |
| Vasculitic ulcers | RA-associated small vessel vasculitis → digital ischaemia → nail fold infarcts, digital ulcers |
High Yield Summary
Complications of limb ischaemia:
- Disease progression: claudication → critical limb ischaemia → gangrene (dry = observe; wet = emergency surgery). CVS events are the main killer (MI/stroke).
- Ischaemia complications: compartment syndrome (pain out of proportion, pain with passive stretch, tense compartment — pulses may be present! → emergency fasciotomy) and rhabdomyolysis (K⁺ → arrhythmia; myoglobin → AKI → aggressive hydration + IV bicarbonate + mannitol ± dialysis).
- Reperfusion injury: oxygen free radicals → tissue damage + WBC sequestration in microcirculation.
Diabetic foot cascade: Neuropathy → deformity + loss of sensation → ulcer → infection → osteomyelitis → amputation. Every step is preventable.
Gout complications: Chronic tophaceous gout (tophi with ulceration/infection), progressive joint destruction, urate stones, uric acid nephropathy. Untreated: 62% second flare within 1 year.
Amputation complications: Early (bleeding, infection, phantom limb pain, skin necrosis); Late (stump ulceration, neuroma, osteomyelitis, fixed flexion deformity, difficult mobilisation). BKA: 90% walk again; AKA: 50%.
Treatment complications: PTA (dissection, distal embolisation, re-stenosis); thrombolysis (stroke, haemorrhage); corticosteroid injection (fascia rupture, fat pad atrophy); allopurinol (AHS with SJS/TEN — HLA-B*5801 screening mandatory in HK Chinese); NSAIDs (GI bleed, AKI, CVS events); fluoroquinolones (Achilles rupture).
Active Recall - Complications of Foot/Toe Pain Conditions
References
[1] Lecture slides: murtagh merge.pdf (p55–56, Foot and ankle pain — serious disorders, pitfalls, masquerades) [3] Senior notes: Ryan Ho Rheumatology.pdf (p23, Ankle and Foot examination — RA deformities; p38, Gout prognosis and tophaceous complications; p40, ULT complications) [4] Senior notes: Ryan Ho Endocrine.pdf (p94, Chronic Diabetic Complications screening; p98, Diabetic Peripheral and Autonomic Neuropathy; p98–99, Diabetic Foot and Charcot Arthropathy) [5] Senior notes: Ryan Ho Cardiology.pdf (p201, Examination of Peripheral Arterial System — pressure areas, skin changes, amputations; p212, Complications — compartment syndrome and rhabdomyolysis; p216, Prognosis for chronic limb ischaemia) [6] Senior notes: felixlai.md (p926, Complications due to ischaemia — compartment syndrome and rhabdomyolysis; p926, Complications due to revascularisation — reperfusion injury; p939–940, Amputation indications, types, and complications) [7] Senior notes: maxim.md (p354, PTA complications; p361, Below-knee management complications — compartment syndrome and rhabdomyolysis; p373, Surgical complications of varicose vein treatment) [8] Senior notes: maxim.md (p538–539, Hallux valgus complications; p539, Pes planus complications; p547–548, Achilles tendinopathy/rupture) [10] Senior notes: Ryan Ho Fundamentals.pdf (p144, Ankle and Foot examination — RA deformities, Morton's neuroma) [12] Senior notes: Ryan Ho Neurology.pdf (p179–180, Peripheral nerve disease clinical features — trophic changes, skeletal deformities, entrapment neuropathy)
High Yield Summary
Definition: Foot/toe pain is a syndromic presentation requiring localisation (forefoot/midfoot/hindfoot) and categorisation (traumatic/mechanical/inflammatory/vascular/neuropathic/infectious/neoplastic) to reach a diagnosis.
Epidemiology: Affects 17–24% of adults; higher in elderly, diabetics, obese. In HK: gout, diabetic foot, hallux valgus, PAD are especially prevalent.
Anatomy: 26 bones, 3 arches (medial longitudinal most clinically important), key structures: plantar fascia (windlass mechanism), Achilles tendon (watershed zone 2–6 cm), tibialis posterior (MLA stabiliser), tarsal tunnel (tibial nerve), intermetatarsal space (Morton's neuroma).
Key aetiologies by location:
- Forefoot: Gout (1st MTPJ), hallux valgus, Morton's neuroma, metatarsalgia, stress fracture, sesamoiditis
- Midfoot: Lisfranc injury, Charcot arthropathy, tarsal coalition
- Hindfoot: Plantar fasciitis (MC cause of heel pain), Achilles tendinopathy/rupture, calcaneal fracture, tarsal tunnel syndrome, retrocalcaneal bursitis
Vascular: PAD from atherosclerosis — Fontaine stages 1–4; intermittent claudication ("shop window to shop window," obstruction one joint above); rest pain (forefoot/toes, ↑lying flat, ↓dependent, requires opioids); gangrene (dry vs. wet). Buerger's disease in young male smokers.
Neuropathic: Diabetic neuropathy → loss of protective sensation → ulcers + Charcot arthropathy (painless joint destruction). ABPI unreliable in DM (calcified vessels) → use TcPO₂ or TBI.
Key clinical features:
- Plantar fasciitis: first-step heel pain, tender medial calcaneal tuberosity
- Achilles: pain 2–6 cm above insertion, Thompson test for rupture
- Gout: acute red-hot-swollen 1st MTPJ, nocturnal, MSU crystals
- PAD: claudication distance, absent pulses, ABI < 0.9, rest pain relieved by dependency
- Morton's neuroma: Mulder's click, 3rd interspace burning pain
- Charcot: warm swollen painless foot in diabetic patient
Must not miss: Critical limb ischaemia, acute arterial occlusion, septic arthritis, osteomyelitis, necrotising fasciitis, Lisfranc injury, acral melanoma.
High Yield Summary
Murtagh's framework for foot pain:
- Probability: Foot strain, sprained ankle, OA (hallux rigidus), plantar fasciitis, Achilles tendonopathy, tibialis posterior tendonopathy, warts/corns/calluses, ingrown toenail
- Serious: Vascular insufficiency (PAD/Buerger), neoplasia (osteoid osteoma, osteosarcoma, acral melanoma), infection (septic arthritis, osteomyelitis), RA, peripheral neuropathy, CRPS, ruptured Achilles
- Pitfalls: Ruptured tibialis posterior, foreign body, gout, Morton neuroma, tarsal tunnel syndrome, chilblains, stress fracture (navicular), erythema nodosum
- Rarities: Spondyloarthropathies, osteochondritis (Köhler, Freiberg, Sever), glomus tumour, Paget disease
- Masquerades: Diabetes, drugs (fluoroquinolones, diuretics), spinal dysfunction (L5/S1 radiculopathy)
- Non-organic: Always consider psychosocial factors in chronic foot pain
Key DDx principles:
- Hot swollen joint → aspirate → crystals (gout/pseudogout) vs. bacteria (septic arthritis) — they can coexist
- Heel pain → plantar fasciitis is MC (80%) but don't forget Achilles, calcaneal fracture, Sever disease, tarsal tunnel, Baxter's nerve
- Rest pain in foot → critical limb ischaemia vs. peripheral neuropathy (bilateral + glove-stocking vs. unilateral + positional)
- Acute limb ischaemia → 6 Ps; differentiate embolism (AF, acute, complete) vs. thrombosis (chronic PVD, subacute, incomplete)
- Wart vs. corn → lateral squeeze (wart) vs. direct pressure (corn); thrombosed capillaries on paring (wart)
- Warm swollen painless foot in diabetic → Charcot arthropathy (not cellulitis!)
High Yield Summary
Key diagnostic principles for foot/toe pain:
-
Joint aspiration is the MOST IMPORTANT TEST for any acutely swollen joint — send for Gram stain (urgent), culture, crystal microscopy, and cell count. It distinguishes gout (MSU: needle, −ve birefringent) from pseudogout (CPPD: rhomboid, +ve birefringent) from septic arthritis (positive Gram/culture, WBC > 50k).
-
ABI ≤ 0.9 = diagnostic of PAD; < 0.4 = critical ischaemia. ABI > 1.30 = calcified → use TBI instead (especially in DM/ESRD).
-
TcPO₂ > 30 mmHg = adequate wound-healing potential in diabetic foot.
-
Plain XR is first-line for most bony pathology. Always weight-bearing for hallux valgus, pes planus, and Lisfranc.
-
MRI is the problem-solver when XR is negative: stress fracture, early osteomyelitis, soft tissue pathology, subtle Lisfranc injury, Charcot (early).
-
Duplex USG is the first-line imaging for PAD — look for triphasic (normal) → biphasic (single-level) → monophasic (multi-level) waveform changes.
-
Serum urate can be normal during acute gout (12–43%) — defer to 2 weeks post-resolution.
-
Plantar fasciitis is a clinical diagnosis. XR is only to rule out fracture — the heel spur is incidental, not diagnostic.
-
Probe-to-bone test: if probe reaches bone in a diabetic foot ulcer, specificity ~89% for osteomyelitis.
-
NCS useful for: tarsal tunnel syndrome, differentiating axonal vs. demyelinating neuropathy, severity assessment. Not useful for: excluding neuropathy, defining aetiology, CNS pathology.
High Yield Summary
Emergency management priorities:
- Acute limb ischaemia: IV heparin immediately → assess viability → embolectomy / thrombolysis / amputation. Watch for compartment syndrome and rhabdomyolysis post-revascularisation.
- Septic arthritis: aspirate → IV antibiotics → washout. Cartilage destroyed in days if untreated.
- Wet gangrene: emergency debridement/amputation. Dry gangrene can self-amputate.
PAD management:
- Conservative first: smoking cessation, supervised exercise, aspirin, statin, cilostazol (C/I in CHF).
- Surgery only for disabling claudication or critical ischaemia. TASC A/B → endovascular; TASC C/D → surgery. Treat inflow before outflow.
Gout management:
- Acute: NSAIDs / colchicine / steroids (choose based on comorbidities).
- Long-term ULT: allopurinol first-line (HLA-B*5801 screening mandatory in HK Chinese!), target urate < 6 mg/dL. Flare prophylaxis with low-dose colchicine × 3–6 months.
Plantar fasciitis: stepwise — footwear + PT + stretching → ESWT / steroid injection → fasciotomy. Clinical diagnosis; heel spur is incidental.
Achilles: eccentric exercises for tendinopathy (NO steroids!). Rupture < 2 weeks → equinus cast; > 2 weeks/active → surgical repair.
Diabetic foot: multidisciplinary — prevention (annual foot exam, education), insoles (neuropathic), angioplasty (vascular), debridement/amputation (surgical). Charcot: immobilise 3–6 months.
Hallux valgus surgery: Chevron (mild), Scarf (moderate/severe), Lapidus/Keller's (arthritic).
High Yield Summary
Complications of limb ischaemia:
- Disease progression: claudication → critical limb ischaemia → gangrene (dry = observe; wet = emergency surgery). CVS events are the main killer (MI/stroke).
- Ischaemia complications: compartment syndrome (pain out of proportion, pain with passive stretch, tense compartment — pulses may be present! → emergency fasciotomy) and rhabdomyolysis (K⁺ → arrhythmia; myoglobin → AKI → aggressive hydration + IV bicarbonate + mannitol ± dialysis).
- Reperfusion injury: oxygen free radicals → tissue damage + WBC sequestration in microcirculation.
Diabetic foot cascade: Neuropathy → deformity + loss of sensation → ulcer → infection → osteomyelitis → amputation. Every step is preventable.
Gout complications: Chronic tophaceous gout (tophi with ulceration/infection), progressive joint destruction, urate stones, uric acid nephropathy. Untreated: 62% second flare within 1 year.
Amputation complications: Early (bleeding, infection, phantom limb pain, skin necrosis); Late (stump ulceration, neuroma, osteomyelitis, fixed flexion deformity, difficult mobilisation). BKA: 90% walk again; AKA: 50%.
Treatment complications: PTA (dissection, distal embolisation, re-stenosis); thrombolysis (stroke, haemorrhage); corticosteroid injection (fascia rupture, fat pad atrophy); allopurinol (AHS with SJS/TEN — HLA-B*5801 screening mandatory in HK Chinese); NSAIDs (GI bleed, AKI, CVS events); fluoroquinolones (Achilles rupture).
Fever/chills
Fever is an elevation of body temperature above the normal set point, often accompanied by chills (rigors), typically resulting from the release of pyrogenic cytokines in response to infection, inflammation, or other pathological processes.
General Malaise
General malaise is a nonspecific feeling of overall discomfort, illness, or lack of well-being that often accompanies the onset of various acute and chronic diseases.