Infective Tenosynovitis

Infective tenosynovitis is a bacterial infection of the tendon sheath, most commonly affecting the flexor tendons of the hand, characterized by Kanavel's signs including fusiform swelling, flexed posture, tenderness along the sheath, and pain with passive extension.

Exam domain	One-glance essentials
Definition / diagnosis	*Closed space infection of the flexor tendon sheath of the hand* — a surgical emergency diagnosed clinically by Kanavel's 4 cardinal signs ^[1]^[2] Accounts for 2.5–9.4% of all hand infections; most common in working-age adults following penetrating trauma ^[2] Flexor sheath is a sealed synovial tube; thumb and little finger sheaths communicate via radial/ulnar bursae and space of Parona (horseshoe communication) ^[2]^[1]
Epidemiology / risks	Penetrating trauma (thorn, bite, needle) is the primary route; marine injuries in HK (seafood handling) → risk of M. marinum and Vibrio spp. ^[1]^[2] *Risk factors for amputation: DM, renal failure, peripheral vascular disease* — high DM prevalence in HK increases local relevance ^[2]^[3] Immunocompromised patients require broader cover for Gram-negatives and anaerobes in addition to standard organisms ^[2]^[3]
Core mechanism	Penetrating inoculation → bacteria multiply in non-distensible sealed sheath → rising intra-sheath pressure → compression of vincula → tendon ischaemia → necrosis ^[1]^[2] *Most common organisms: Staphylococcus aureus and Streptococcus spp.; polymicrobial in bites and immunocompromised ^[2]^[3] Thumb/little finger infection can spread via bursae → horseshoe abscess* involving opposite digit and forearm (space of Parona) ^[2]^[1]
Clinical picture	*Kanavel's 4 signs: fusiform swelling, flexed posture at rest, tenderness along entire flexor sheath (most sensitive), pain on passive extension (most specific) ^[1]^[2] No other condition produces all 4 Kanavel signs simultaneously — key discriminator from cellulitis* (lacks sheath-specific signs) and felon (pulp only) ^[2] Three "cannot miss" diagnoses in a painful swollen hand: *PFT, septic arthritis, necrotizing fasciitis* — all need emergency surgical intervention ^[2]^[4] Suspect necrotizing fasciitis if pain out of proportion, haemorrhagic bullae, dishwater pus, systemic toxicity, LRINEC score >8 ^[4]^[5]
Investigations	PFT is a clinical diagnosis — *prompt clinical assessment takes priority; investigations are supportive, not gate-keeping; normal bloods do NOT exclude PFT* ^[1]^[2] First-line imaging: X-ray (exclude fracture, foreign body, gas); USS (detect sheath fluid); *MRI is not routine* but best for complications ^[2]^[1] *Bloods: CBP, ESR, CRP* + blood cultures before antibiotics + renal function + glucose/HbA1c for comorbidity screening ^[2]^[3] Gold standard: intra-operative sheath fluid/tissue biopsy → Gram stain, C/ST (aerobic, anaerobic, AFB, fungal); alert lab if M. marinum (30–32°C) or N. gonorrhoeae suspected ^[2]^[6]
Management	*3–4 Kanavel signs → surgical emergency* (drainage + IV antibiotics); *1–2 signs → trial of IV antibiotics with reassessment at 24 hours* ^[1]^[2] *Empirical IV cloxacillin to cover Staph + Strep; add Gram-negative and anaerobic cover in immunocompromised or bite wounds ^[2]^[7] Closed catheter irrigation* for moderate infection without necrosis; *open irrigation and debridement (zig-zag incision)* for advanced/necrotic/chronic infection — preserve A2 and A4 pulleys ^[1]^[2] Non-operative pathway requires elevation, splinting, frequent examination — *no improvement after 24–48 hours → proceed to surgery* ^[2]^[3]
Complications	Tendon necrosis is the most feared complication — vincular compression causes irreversible ischaemia within 24–48 hours; this is why PFT is a surgical emergency ^[1]^[2] Tendon adhesions and stiffness are the most common long-term sequelae even after successful treatment; early rehabilitation is essential ^[2]^[8] Contiguous spread → septic arthritis, osteomyelitis, deep space infection; systemic spread → sepsis, necrotizing fasciitis (potentially fatal) ^[2]^[4] *Amputation in 46% of HK patients with hand NF; mortality 20–75%; iatrogenic pulley damage → bowstringing*; CRPS and chronic pain may follow ^[2]^[8]
Prevention / follow-up	Thorough wound irrigation and debridement after penetrating hand injuries; early antibiotic prophylaxis for contaminated wounds and bite injuries ^[3]^[6] Post-operative early rehabilitation (supervised active mobilisation) to prevent tendon adhesions and stiffness — the most common chronic complication ^[2]^[8] Optimise DM control, renal function, and vascular status pre- and post-operatively to reduce amputation risk ^[2]^[3]
Exam traps	Normal inflammatory markers do NOT exclude PFT — treat the patient, not the blood test; delayed surgery awaiting results → irreversible tendon necrosis ^[2]^[1] Commonest diagnostic pitfall is PFT vs cellulitis — cellulitis lacks fusiform swelling, flexed posture, and pain on passive extension; always check sheath-specific signs ^[2] Sausage digit has a broad DDx (PFT, dactylitis, gout) — acute onset + wound + Kanavel signs = PFT until proven otherwise ^[2]^[9] PFT can coexist with or evolve from adjacent infections (felon → PFT → septic arthritis → osteomyelitis) — always reassess for progression ^[2]^[4]

References

^[1] Lecture slides: GC 237. Musculoskeletal infection [Updated in 2025] (1).pdf (pages 2, 3, 24, 28, 29, 32, 44, 54) ^[2] Senior notes: maxim.md (sections 504–508: tendon-related pathology, De Quervain's, trigger finger, ganglion cyst, Kanavel signs) ^[3] Lecture slides: GC 237. Musculoskeletal infection [Updated in 2025] (1).pdf (pages 2, 3, 24, 28, 29, 30, 32, 33, 54) ^[4] Senior notes: maxim.md (sections 564, 566–567: necrotizing fasciitis, osteomyelitis, septic arthritis, LRINEC score) ^[5] Senior notes: maxim.md (sections 565–567: osteomyelitis, septic arthritis, necrotizing fasciitis, gas gangrene, LRINEC score) ^[6] Senior notes: maxim.md (section 59: surgical site infection — wound swab for culture, CT with contrast for deep infection) ^[7] Senior notes: maxim.md (sections 566–567: osteomyelitis, septic arthritis — IV cloxacillin regimens, ceftriaxone for NG) ^[8] Senior notes: maxim.md (section 454: complications of trauma — compartment syndrome, adhesions, CRPS, Volkmann's contracture); felixlai.md (section 1381: amputation — 3D indications, complications) ^[9] Senior notes: maxim.md (section 446: differential diagnosis tiers — TIN framework)

Pyogenic flexor tenosynovitis (PFT) is a closed space infection of the flexor tendon sheath of the hand ^[1]. Let's break the name down:

"Pyogenic" → pyo (Greek: pus) + genic (producing) = pus-producing
"Flexor" → the flexor tendons of the fingers (which bend the fingers)
"Tenosynovitis" → teno (tendon) + syno (synovial membrane) + itis (inflammation) = inflammation of the synovial sheath surrounding a tendon

So the name literally tells you: this is a pus-producing infection of the synovial sheath that surrounds the flexor tendons of the finger. It is an orthopaedic/hand surgery emergency because the tendon sheath is a closed space — once pus accumulates, pressure rises rapidly and can destroy the tendon and its blood supply within hours.

It accounts for approximately 2.5 to 9.4% of all hand infections ^[1].

Why is this an emergency?

The flexor tendon sheath is a sealed, low-compliance compartment. Infection → pus → rising pressure within a non-distensible space → compression of the vincula (the tiny vessels that supply the tendon) → tendon ischaemia and necrosis. This is exactly the same principle as compartment syndrome, just on a miniature scale. A missed or delayed diagnosis can lead to a stiff, non-functional finger or even amputation.

Distinguish the terminology ^[2]:

Tendinosis: age-related degeneration of a tendon (no inflammation)

Tendinitis: inflammation of the tendon itself

Tenosynovitis: inflammation of the synovial sheath

Tenovaginitis: inflammation of the fibrous sheath (pulley)

Infective tenosynovitis specifically refers to bacterial infection within the synovial sheath.

Represents 2.5–9.4% of all hand infections ^[1]
Most common mechanism: penetrating trauma (thorn prick, knife cut, bite wound, needle stick) introducing bacteria directly into the tendon sheath
Can also occur via contiguous spread from a nearby felon, paronychia, or septic arthritis of a small joint, or rarely by haematogenous spread
Male predominance (occupational exposure)
Peak incidence in working-age adults (20–50 years) due to occupational and recreational hand injuries
The index and middle fingers of the dominant hand are most commonly affected (greatest exposure to trauma)
In Hong Kong, consider:
- Injuries from fish bones and seafood handling (Gram-negative organisms including Vibrio, Mycobacterium marinum)
- Diabetes mellitus is highly prevalent and is a major risk factor for severe infection and poor outcomes

3. Risk Factors

Risk factors for amputation include ^[1]:

Diabetes mellitus (DM) — impaired neutrophil function, microangiopathy reduces local perfusion and antibiotic delivery
Renal failure — uraemic immunosuppression, impaired wound healing
Peripheral vascular disease — poor tissue perfusion, reduced local immune response and antibiotic penetration

Additional risk factors (general for musculoskeletal infection):

Immunocompromised states (HIV, chronic steroid use, malignancy on treatment) ^[1]
Liver disease / cirrhosis — impaired opsonisation, reduced complement, predisposes to Vibrio vulnificus (relevant in Hong Kong with raw seafood exposure) ^[1]
Drug abuse (IV) — direct inoculation, often polymicrobial ^[1]
Age > 60 ^[1]
Alcohol abuse ^[1]

Penetrating trauma: the single most common cause — a puncture wound (thorn, nail, fish bone, animal/human bite) directly inoculates bacteria into the closed sheath
Human bites / fight bites: high risk of polymicrobial infection including anaerobes
Animal bites: Pasteurella multocida (cats/dogs)
Marine injuries: Mycobacterium marinum, Vibrio species — especially relevant in Hong Kong
Adjacent soft tissue infection: contiguous spread from paronychia, felon, or web space abscess
Post-surgical / post-injection: iatrogenic inoculation

Hong Kong-Specific Consideration

In the Hong Kong clinical context, always ask about seafood handling and marine exposure. Fish bone injuries and handling raw shellfish can introduce Mycobacterium marinum (causing chronic granulomatous tenosynovitis) or Vibrio vulnificus (fulminant infection in patients with liver disease). The clinical trajectory is very different — M. marinum is indolent whereas Vibrio is rapidly fatal in the immunocompromised.

4. Anatomy and Function

Understanding the anatomy is critical because it explains every single clinical sign, why infection spreads in certain patterns, and why surgical approaches differ.

Each finger (index through little) has a digital flexor tendon sheath — a closed, tubular, synovial membrane that surrounds:

Flexor digitorum superficialis (FDS) — inserts on the middle phalanx; flexes the PIP joint
Flexor digitorum profundus (FDP) — inserts on the distal phalanx; flexes the DIP joint

The sheath has two layers:

Visceral layer (epitenon): directly adherent to the tendon surface
Parietal layer: lines the inner surface of the fibrous sheath

Between them is the synovial cavity — a potential space containing a thin film of synovial fluid for lubrication. This is the space that gets infected in PFT.

The fibrous sheath (outer to the synovial sheath) forms the pulley system, which prevents bowstringing of the flexor tendons during finger flexion ^[2]:

Annular pulleys (A1–A5): A1, A3, A5 overlie the MCPJ, PIPJ, and DIPJ respectively; A2 (proximal phalanx) and A4 (middle phalanx) are the most biomechanically important
Cruciate pulleys (C1–C3): between the annular pulleys, allow sheath flexibility

The pulley system is relevant because it defines the rigid boundaries of the closed space. Pus trapped between pulleys has nowhere to go except proximally and distally along the sheath.

This is the single most important anatomical concept for PFT:

The digital sheaths of the index, middle, and ring fingers are discrete — they start at the level of the A1 pulley (at the neck of the metacarpal) and end at the distal phalanx. They are closed-ended compartments.
The thumb has a flexor sheath that is continuous with the radial bursa.
The little finger has a flexor sheath that is continuous with the ulnar bursa.
The radial and ulnar bursae communicate at the space of Parona (a potential space deep to the pronator quadratus in the distal forearm, just proximal to the carpal tunnel).

This creates a "horseshoe" (or "U-shaped") communication between the thumb and little finger sheaths via the radial bursa → space of Parona → ulnar bursa.

Clinical Pearl — Horseshoe Abscess

If PFT of the thumb or little finger is not treated promptly, infection can track along this horseshoe communication to involve the opposite digit and the space of Parona in the forearm. This is called a "horseshoe abscess" — a devastating complication. This is why PFT of the thumb and little finger is considered more dangerous than PFT of the index, middle, or ring fingers, whose sheaths are self-contained.

Within the digital sheath, the tendons receive their blood supply from:

Vincula longa and brevia — small mesenteric-like folds (mesotendon remnants) carrying vessels from the digital arteries to the tendon surface
Diffusion from synovial fluid within the sheath

When infection causes elevated pressure within the sheath, the vincula are compressed first → tendon ischaemia → necrosis. This is why prompt decompression is essential.

The dorsal side of the wrist has six extensor compartments ^[2]:

APL & EPB (De Quervain's involves this compartment)
ECRL & ECRB
EPL
ED & EI
EDM
ECU

Infective tenosynovitis can occur in extensor sheaths too, but it is far less common and less dangerous because the extensor sheaths are not as tightly enclosed as the flexor sheaths.

5. Etiology and Pathophysiology

Empirical antibiotics should cover Staphylococcus and Streptococcus species ^[1]. Antibiotics should cover gram-negative rods and anaerobes in case of immunocompromised patients ^[1].

Organism	Context
*Staphylococcus aureus*	Most common overall (~40–75% of cases). Penetrating trauma, skin flora
*Streptococcus spp.* (Group A β-haemolytic Strep = S. pyogenes)	Second most common. Can spread rapidly
MRSA	Consider in IV drug users, healthcare-associated infections, recurrent infections
*Gram-negative rods* (e.g. Pseudomonas, E. coli, Eikenella)	*Immunocompromised patients*, IV drug users, bite wounds
*Anaerobes*	*Immunocompromised patients*, bite wounds, deep wounds
Pasteurella multocida	Cat/dog bites (inoculated from animal oral flora)
Eikenella corrodens	Human bites / fight bites (human oral flora)
Mycobacterium marinum	Marine/aquarium exposure — important in Hong Kong (fish bone injuries, seafood handling). Causes chronic granulomatous tenosynovitis. Indolent course
Neisseria gonorrhoeae	Disseminated gonococcal infection — haematogenous spread, often polyarticular. Consider in young sexually active patients
Polymicrobial	Bite wounds, diabetic patients, immunocompromised
Fungal (Candida, Sporothrix)	Rare. Immunocompromised, gardeners (sporotrichosis)

Direct inoculation (most common): penetrating trauma introduces skin flora or environmental organisms into the tendon sheath
Contiguous spread: from adjacent soft tissue infection (paronychia, felon, web space abscess, septic arthritis of PIPJ/MCPJ)
Haematogenous spread: bacteraemia seeds the synovial sheath (rare; think N. gonorrhoeae or S. aureus bacteraemia)

Inoculation: bacteria enter the closed synovial sheath via one of the above mechanisms
Bacterial proliferation: the synovial fluid is a warm, nutrient-rich, relatively immune-privileged environment (poor blood supply, enclosed space) → ideal for bacterial growth
Inflammatory response: neutrophil recruitment → purulent exudate fills the sheath → intra-sheath pressure rises
Vascular compromise: rising pressure compresses the vincula (the tendon's blood supply) → tendon ischaemia
Tendon necrosis: prolonged ischaemia (typically > 24–48 hours of untreated infection) leads to tendon necrosis and adhesion formation
Potential spread:
- Along the sheath (proximal/distal)
- Into the midpalmar space or thenar space
- Via the horseshoe communication (thumb ↔ little finger via radial/ulnar bursae and space of Parona)
- To bone → osteomyelitis of phalanges
- Into the carpal tunnel
- Into the forearm (space of Parona → Parona's abscess)
Systemic spread: if untreated → bacteraemia → sepsis

Time is Tendon

The pathophysiology parallels compartment syndrome. Once pressure in the closed sheath exceeds perfusion pressure of the vincula, the tendon starts dying. Every hour of delay worsens outcomes. This is why PFT is a surgical emergency — the goal is to decompress the sheath and drain pus before irreversible tendon damage occurs.

6. Classification

There is no universally accepted formal staging system, but clinical severity is often graded by the number of Kanavel signs present (see Clinical Features section) and response to treatment:

Category	Description
Early / Low suspicion	1–2 Kanavel signs, mild symptoms, early infection
Established / High suspicion	*3–4 Kanavel signs, moderate/severe symptoms* ^[1]
Advanced / Complicated	Necrosis, abscess formation, proximal spread (horseshoe abscess), osteomyelitis

The management protocol flow chart ^[1] uses this classification to guide surgical vs non-surgical treatment:

Low clinical suspicion for PFT, mild clinical symptoms, 1–2 Kanavel signs, early infection → Non-surgical treatment with empiric antibiotic coverage ^[1]
High clinical suspicion for PFT, 3–4 Kanavel signs, moderate/severe symptoms → Surgical treatment + empiric antibiotic coverage ^[1]

Category	Examples
Acute pyogenic	S. aureus, Streptococcus, Gram-negatives
Chronic granulomatous	Mycobacterium marinum, M. tuberculosis, fungi
Gonococcal	N. gonorrhoeae (haematogenous)
Polymicrobial	Bite wounds, diabetic patients

Post-traumatic (most common)
Contiguous spread (from adjacent infection)
Haematogenous (disseminated infection)

7. Clinical Features

The clinical hallmark of PFT is the four Kanavel signs, described by Allen B. Kanavel in 1912. These are the most important clinical features to know for exams.

Symptom	Pathophysiological Basis
Severe finger pain — throbbing, progressive, disproportionate to the external wound	Pus accumulating in a non-distensible closed space → rapidly rising pressure → stimulation of nociceptors in the peritendinous tissue and sheath
Pain worsened by any finger movement (especially passive extension)	Passive extension stretches the inflamed tendon sheath and increases intra-sheath pressure, stimulating pain fibres. This is analogous to why passive stretch is painful in compartment syndrome
Stiffness / inability to move the finger	Swelling and pain inhibit active flexion/extension; later, tendon adhesions physically restrict movement
Swelling of the entire finger	Inflammatory oedema within and around the closed sheath distributes along the whole length of the tendon → uniform ("sausage-like") swelling
History of penetrating trauma (often a small, seemingly trivial wound)	Direct inoculation mechanism — patients often present days after the initial injury because the wound appeared minor
Systemic symptoms (fever, malaise) — in advanced cases	Cytokine release and potential bacteraemia

These are the cardinal signs of pyogenic flexor tenosynovitis. They directly reflect the underlying pathophysiology:

#	*Kanavel Sign*	Explanation / Pathophysiological Basis
1	*Fusiform (sausage-shaped/symmetric) swelling of the entire finger*	The synovial sheath runs the full length of the digit from the A1 pulley to the DIP. Pus/inflammatory fluid distends the sheath uniformly, making the finger swell symmetrically along its entire length (fusiform = spindle-shaped). This contrasts with a localised abscess which causes focal swelling
2	*Flexed posture of the finger at rest*	The distended sheath holds the greatest volume when the finger is slightly flexed (the sheath is lax in flexion). Extension would compress the sheath and increase pressure → the patient instinctively holds the finger in a semiflexed position to minimise pain. Additionally, the flexors are stronger than extensors, and inflammation/spasm of the flexor muscles contributes
3	*Tenderness along the entire flexor tendon sheath* (from the proximal palm to the fingertip)	The infection involves the entire length of the closed sheath, so pressure on any part of it causes pain. This is the most sensitive Kanavel sign. Tenderness is maximal over the proximal sheath (A1 pulley area at the palmar crease) because this is where the sheath begins and pus tends to collect by gravity
4	*Excruciating pain on passive extension of the finger*	Passive extension stretches the inflamed, distended tendon sheath and increases intra-sheath pressure → intense pain. This is the most specific Kanavel sign. It is analogous to "pain on passive stretch" in compartment syndrome

High Yield — Kanavel Signs

The 4 Kanavel signs are the clinical cornerstone of diagnosing PFT:

Fusiform swelling of the entire finger
Flexed posture at rest
Tenderness along the entire flexor sheath (most sensitive)
Pain on passive extension (most specific)

The presence of 3–4 Kanavel signs indicates high clinical suspicion and warrants surgical treatment ^[1]. Only 1–2 signs with mild symptoms may be trialled with antibiotics alone, but close monitoring is mandatory.

Sign	Significance
Small wound / puncture mark on the volar aspect of the finger	The portal of entry — often deceptively small
Erythema of the finger	Local inflammatory response
Warmth	Hyperaemia from inflammation
Lymphangitis / lymphadenopathy (red streaking up the arm, axillary lymph nodes)	Spread of infection via lymphatic drainage
Fever, tachycardia	Systemic inflammatory response; suggests bacteraemia or sepsis
Fluctuance (late sign)	Abscess formation — indicates advanced infection
Proximal palm / wrist tenderness	Suggests proximal extension into the radial/ulnar bursa or space of Parona
Thumb AND little finger both involved	Horseshoe abscess — infection has tracked through the radial bursa → space of Parona → ulnar bursa (or vice versa)

7.4 Special Scenarios

When PFT of the little finger extends proximally through the ulnar bursa → space of Parona → radial bursa → involves the thumb (or vice versa)
Presents with swelling and tenderness of both the thumb and little finger plus distal forearm swelling/tenderness
This is a catastrophic complication requiring extensive surgical debridement

Indolent course over weeks to months (not acute)
Sausage digit with mild tenderness
History of aquarium exposure, fish tank, seafood handling
May track along the sheath to form "sporotrichoid" nodules (ascending nodules along lymphatics)
Requires prolonged antibiotic therapy (rifampicin + ethambutol or clarithromycin) ± surgical debridement

Young, sexually active patient
Often multiple tendons involved (polytenosynovitis) — wrists, ankles, fingers
Associated with migratory polyarthralgia, dermatitis (pustular skin lesions)
Part of disseminated gonococcal infection (DGI)
Diagnosis: NAAT of genital/rectal/pharyngeal swabs, blood cultures, joint aspirate

Exam Trap

Do not confuse infective tenosynovitis with De Quervain's tenosynovitis (which is a non-infective, mechanical/overuse stenosing tenovaginitis of the 1st extensor compartment) or trigger finger (stenosing tenovaginitis of the A1 pulley). The key discriminator is the presence of infection — fever, an inoculating wound, all 4 Kanavel signs, and systemic toxicity are absent in De Quervain's and trigger finger.

Common musculoskeletal infections that you cannot miss ^[1]:

Bone and joint infections: septic arthritis, osteomyelitis
Soft tissue infections: paronychia, soft tissue abscess, infective tenosynovitis, necrotizing fasciitis, gas gangrene

PFT sits among these as a soft tissue infection of the hand that, if missed, can progress to septic arthritis of adjacent joints, osteomyelitis of phalanges, necrotizing fasciitis, or sepsis.

The hand has several deep spaces that can become involved as PFT spreads:

Thenar space: deep to thenar muscles, radial to midpalmar septum
Midpalmar space: between metacarpals and palmar aponeurosis, ulnar to midpalmar septum
Hypothenar space: deep to hypothenar muscles
Web spaces: between fingers
Space of Parona: in the distal forearm, deep to pronator quadratus

Understanding these spaces explains why untreated PFT can lead to devastating deep hand infections.

High Yield Summary

Infective (Pyogenic Flexor) Tenosynovitis — Key Points:

Definition: Closed space infection of the flexor tendon sheath of the hand — a surgical emergency
Epidemiology: 2.5–9.4% of all hand infections; most common in working-age adults after penetrating trauma
Most common organisms: Staphylococcus aureus and Streptococcus spp.; cover Gram-negatives and anaerobes in immunocompromised
Anatomy: The flexor tendon sheath is a sealed synovial tube; thumb and little finger sheaths communicate via the radial/ulnar bursae and space of Parona (horseshoe communication)
Pathophysiology: Infection in a non-distensible closed space → rising pressure → compression of vincula → tendon ischaemia → necrosis. Time is tendon.
Kanavel Signs (4):
- Fusiform (sausage) swelling of the entire finger
- Flexed posture at rest
- Tenderness along the entire flexor sheath (most sensitive)
- Pain on passive extension (most specific)
Risk factors for amputation: DM, renal failure, peripheral vascular disease
Management threshold: 1–2 Kanavel signs → trial of antibiotics; 3–4 Kanavel signs → surgical drainage + antibiotics
Hong Kong relevance: Marine injuries (M. marinum, Vibrio) from seafood handling; high DM prevalence

Active Recall - Infective Tenosynovitis

^[1] Lecture slides: GC 237. Musculoskeletal infection [Updated in 2025] (1).pdf (pages 2, 3, 24, 28, 32, 33) ^[2] Senior notes: maxim.md (sections 504–506: tendon-related pathology, trigger finger)

Differential Diagnosis of Infective (Pyogenic Flexor) Tenosynovitis

The differential diagnosis of a swollen, painful finger is broader than you might think. The key clinical challenge is distinguishing pyogenic flexor tenosynovitis (PFT) — a surgical emergency — from conditions that can mimic it. Let's work through this systematically, grouping differentials by anatomical location and pathological process, and explaining why each condition can be confused with PFT and how to tell them apart.

Before diving into differentials, recall what defines PFT clinically — the 4 Kanavel signs ^[1]:

Fusiform (symmetrical) swelling of the entire finger
Flexed posture of the involved digit
Tenderness over and limited to the flexor sheath
Severe pain on passive extension of the finger (especially proximally)

Any condition that causes a swollen, painful, stiff finger can mimic PFT. The differentials can be organised by the TIN framework (Trauma, Infection, Neoplasm) plus Inflammatory, Metabolic, Degenerative, and Vascular categories ^[3].

Differential	Why It Mimics PFT	How to Distinguish from PFT
Felon (pulp space abscess)	Painful, swollen fingertip; may coexist with or spread to cause PFT	Swelling and tenderness confined to the distal pulp (volar pad of fingertip), not along the entire flexor sheath. No fusiform swelling of the whole digit. No pain on passive extension of PIPJ/MCPJ. The pulp is a separate closed compartment (septae of Grayson's ligaments) distinct from the tendon sheath
Paronychia	Painful, swollen periungual area; can spread contiguously to cause PFT	Swelling and erythema localised to the nail fold (lateral or proximal). Pus may be visible under the cuticle. No tenderness along the proximal flexor sheath. No flexed posture
Herpetic whitlow	Painful vesicular lesion on the fingertip; can be mistaken for a felon or early PFT	Grouped vesicles on an erythematous base on the fingertip. Viral prodrome (tingling/burning). Often in healthcare workers (HSV exposure). Do NOT incise — will spread the virus. Tzanck smear or viral PCR confirms
Septic arthritis of PIPJ, DIPJ, or MCPJ	Hot, swollen, painful joint; limited ROM; fever	Pain and swelling localised to one joint, not along the entire sheath. Tenderness is periarticular, not along the whole flexor sheath. Hot, swollen, tender joint; patient holds joint in flexion; gross limitation of motion ^[1]. Joint aspiration: WBC > 50,000/mm³, > 75% PMN, positive Gram stain (60–80%) ^[1]. Can coexist with PFT (contiguous spread)
Subcutaneous abscess / cellulitis of the finger	Red, swollen, painful finger	Cellulitis: diffuse erythema with ill-defined borders, warmth, but no fusiform swelling along the sheath and no pain on passive extension. Abscess: focal fluctuant collection, not tracking along the tendon sheath. Tenderness is superficial and not limited to the flexor sheath pathway
Gout / pseudogout (crystal arthropathy)	Acute monoarthritis of a finger joint — exquisitely painful, red, swollen	Usually affects one joint (MCPJ, PIPJ, or 1st MTPJ in foot). History of prior attacks, tophi, elevated urate. Joint aspirate: negatively birefringent needle-shaped crystals (gout) or positively birefringent rhomboid crystals (pseudogout). No tenderness along the entire flexor sheath
Trigger finger (stenosing tenovaginitis of A1 pulley) ^[2]	Finger locked in flexion — mimics the "flexed posture" Kanavel sign	Clicking or locking in flexion at the A1 pulley level (over MCPJ), not along the entire sheath. No signs of infection (no fever, no erythema, no warmth). Tenderness is focal over the A1 pulley only, not fusiform. Chronic and mechanical, not acute and infective. Green's classification grades I–IV ^[2]
De Quervain's tenosynovitis ^[2]	Painful tendon sheath pathology; the word "tenosynovitis" itself causes confusion	This is a non-infective, stenosing tenovaginitis of the 1st extensor compartment (APL & EPB) on the dorsal/radial side of the wrist, not the flexor sheath of a digit ^[2]. Positive Finkelstein's test ^[2]. No fever, no fusiform digital swelling
Flexor tendon injury / rupture	Pain, swelling, inability to flex the finger	History of acute laceration or forced extension injury. Inability to actively flex DIP (FDP injury) or PIP (FDS injury). No signs of infection acutely. Tenodesis effect absent for the ruptured tendon
Fracture of phalanx	Pain, swelling, inability to move the finger; may have flexed posture due to pain	History of direct trauma. Point tenderness over bone, not along the flexor sheath. Deformity, crepitus may be present. X-ray will show fracture line. No systemic infective features
Dislocation of PIPJ or DIPJ	Painful, swollen, deformed finger held in abnormal position	Obvious deformity at the joint. History of hyperextension or axial loading injury. Reducible. X-ray diagnostic
Necrotizing fasciitis	Severe pain, swelling, systemic toxicity — can start in the hand	Pain out of proportion to clinical signs; haemorrhagic bullae; dirty "dishwater" discharge; systemic toxicity ^[1] ^[4]. Rapidly progressive. Skin changes (dusky, necrotic) evolve faster than PFT. Finger probe test positive (minimal resistance to blunt dissection through fascial planes) ^[4]. LRINEC score > 8 = high risk ^[4]. This is a life-threatening emergency
Osteomyelitis of phalanx	Chronic painful swollen finger with limited ROM	Usually insidious onset (unless acute haematogenous). Draining sinus tract may be present in chronic cases ^[4]. X-ray: periosteal reaction, lytic lesions (may be normal in acute phase). MRI is best for diagnosis ^[4]. Can coexist with PFT (contiguous spread from tendon sheath to bone)
Ganglion cyst ^[2]	Swelling on the finger or wrist	Solitary spherical painless smooth cystic lesion; transilluminable ^[2]. Non-tender, no signs of infection. Chronic, not acute. Located at joint capsule or tendon sheath but does not cause fusiform swelling of the entire digit
Disseminated gonococcal infection (DGI)	Tenosynovitis (often multiple tendons) + arthritis	Young sexually active patient. Polytenosynovitis (multiple tendons of wrists/ankles/fingers — not isolated to one digit). Migratory polyarthralgia. Dermatitis (scattered painless pustules on trunk/extremities). Blood/genital NAAT positive. Joint aspirate often culture-negative
Gout tophi / rheumatoid nodule	Chronic nodular swelling near finger joints	Non-tender (unless flaring), chronic, no acute infective features. Tophi: chalky white deposits. RA nodules: firm subcutaneous nodules at pressure points
Foreign body reaction / retained foreign body	Painful swollen finger after penetrating injury	History of penetrating trauma (same as PFT!). May have a palpable foreign body. X-ray may show radiopaque material (glass, metal). If foreign body is within the tendon sheath, it can cause secondary PFT — so these coexist. Ultrasound helps identify non-radiopaque foreign bodies

When you're standing at the bedside trying to decide if this is PFT or something else, focus on these discriminators:

Feature	PFT	Felon	Paronychia	Cellulitis	Septic arthritis	Necrotizing fasciitis
Distribution of swelling	Entire digit (fusiform)	Distal pulp only	Nail fold only	Diffuse, ill-defined	Periarticular, one joint	May extend beyond digit
Tenderness distribution	Along entire flexor sheath	Distal pulp	Periungual	Diffuse, superficial	Periarticular	Deep, out of proportion
Pain on passive extension	Yes — severe	No	No	Minimal	Yes (at affected joint only)	Yes but diffuse
Flexed posture	Yes	No	No	No	Yes (at one joint)	Variable
Skin changes	Erythema	Tense pulp	Erythema at nail fold	Spreading erythema	Erythema over joint	Haemorrhagic bullae, dusky skin, necrosis ^[4]
Systemic toxicity	Moderate (late)	Mild	Mild	Moderate	Moderate	Severe, early ^[4]
Speed of progression	Hours to days	Days	Days	Days	Hours to days	Hours — rapidly progressive ^[4]

The Critical 'Do Not Miss' Diagnoses

When evaluating a swollen painful finger/hand, the three diagnoses you cannot miss because of devastating consequences are ^[1]:

Pyogenic flexor tenosynovitis → tendon necrosis, stiff finger, amputation
Septic arthritis → joint destruction
Necrotizing fasciitis → limb loss, death

All three require early recognition and early surgical intervention + empirical antibiotics ^[1]. If in doubt, treat as the most dangerous diagnosis first.

Step 1: Is this infective or non-infective?

Infective: fever, wound/portal of entry, leucocytosis, elevated CRP, rapid onset
Non-infective: chronic/mechanical symptoms, no systemic features (trigger finger, De Quervain's, ganglion)

Step 2: If infective — where exactly is the infection?

Tendon sheath → PFT (fusiform swelling, all 4 Kanavel signs)
Joint → Septic arthritis (periarticular swelling, pain with any joint movement, aspiration diagnostic)
Pulp → Felon (focal distal swelling)
Nail fold → Paronychia
Subcutaneous tissue → Cellulitis/abscess
Fascia/deep planes → Necrotizing fasciitis (pain out of proportion, systemic toxicity, skin necrosis)
Bone → Osteomyelitis (usually subacute/chronic unless haematogenous)

Step 3: If the whole finger is swollen ("sausage digit"), think of:

Acute	Chronic
PFT (infective)	Psoriatic dactylitis (inflammatory)
Septic arthritis (may overlap)	Reactive arthritis (Reiter's)
Gout flare	Sarcoidosis
Fracture with haematoma	TB dactylitis (spina ventosa)
	Sickle cell dactylitis (children)

The acute sausage digit with Kanavel signs + a wound is PFT until proven otherwise.

Step 4: Check for coexisting/evolving pathology

PFT can arise from a felon or paronychia (contiguous spread)
PFT can progress to septic arthritis, osteomyelitis, deep space infection, or necrotizing fasciitis
Always examine for proximal spread (palm, wrist, forearm) — suggests horseshoe abscess or deep space involvement

Practical Tip

In the exam or clinical setting, if you're given a scenario of a painful swollen finger after a penetrating injury and you can identify tenderness along the entire flexor sheath + pain on passive extension, that is essentially pathognomonic for PFT. The other conditions do not produce this combination. State the diagnosis confidently — don't hedge with a long differential when the Kanavel signs are clearly present.

Special DDx Scenarios Worth Knowing

This is the commonest clinical dilemma. Both cause a red, swollen, painful finger after a wound. The key is that in cellulitis, the inflammation is in the subcutaneous tissue, not the tendon sheath. So:

Cellulitis: erythema is superficial and spreading, tenderness is diffuse (not along the sheath), no pain on passive extension, no fusiform swelling (irregular swelling instead), no flexed posture
PFT: tenderness tracks along the sheath from palm to fingertip, pain on passive extension is marked

An acute gout attack at the MCPJ or PIPJ can produce a red, swollen, exquisitely tender finger. However:

Gout: periarticular swelling at one joint, not fusiform along the entire digit. History of prior attacks, hyperuricaemia, tophi. Joint aspiration with polarised microscopy showing negatively birefringent urate crystals is diagnostic ^[4]
PFT: tenderness along the entire sheath, not limited to one joint

DGI can cause tenosynovitis, but it is characteristically polytenosynovitis (multiple tendons, often wrists and ankles, not just one finger). Associated features include migratory polyarthralgia and a characteristic dermatitis (scattered painless pustules). The patient is typically young and sexually active.

High Yield Summary

Differential Diagnosis of Infective Tenosynovitis — Key Takeaways:

The 4 Kanavel signs are the primary discriminators — no other condition produces all four simultaneously
Pain on passive extension (most specific) and tenderness along the entire flexor sheath (most sensitive) are the best signs to distinguish PFT from other finger infections
Three "cannot miss" diagnoses in a painful swollen hand: PFT, septic arthritis, necrotizing fasciitis — all require emergency surgical intervention ^[1]
Commonest diagnostic dilemma is PFT vs cellulitis — look for sheath-specific signs (fusiform swelling, flexed posture, pain on passive extension)
Sausage digit has a broad differential (PFT, dactylitis, gout) — acute onset + wound + Kanavel signs = PFT
PFT can coexist with or evolve from/into adjacent infections (felon → PFT → septic arthritis → osteomyelitis → deep space infection)
Necrotizing fasciitis: pain out of proportion, haemorrhagic bullae, systemic toxicity, dishwater pus, LRINEC > 8 ^[1] ^[4]

Active Recall - DDx of Infective Tenosynovitis

References

^[1] Lecture slides: GC 237. Musculoskeletal infection [Updated in 2025] (1).pdf (pages 2, 3, 24, 27, 28, 32, 41, 54) ^[2] Senior notes: maxim.md (sections 504–508: tendon-related pathology, De Quervain's, trigger finger, ganglion cyst, Kanavel signs) ^[3] Senior notes: maxim.md (section 446: differential diagnosis tiers — TIN framework) ^[4] Senior notes: maxim.md (sections 564, 566–567: necrotizing fasciitis, osteomyelitis, septic arthritis, LRINEC score)

Diagnostic Criteria, Diagnostic Algorithm, and Investigations for Infective (Pyogenic Flexor) Tenosynovitis

1. Diagnostic Criteria

PFT is fundamentally a clinical diagnosis. There is no single laboratory test or imaging study that confirms it — the diagnosis rests on recognising the clinical pattern at the bedside. This is why Kanavel's cardinal signs, described in 1912, remain the diagnostic gold standard over a century later.

Kanavel's Cardinal Signs (described in 1912) ^[1]:

#	Sign	Sensitivity / Specificity	Pathophysiological Basis
1	Tenderness over and limited to the flexor sheath	Most sensitive (~91–97%)	The entire synovial sheath is inflamed and distended with pus → pressure on any point along the sheath (from the distal palmar crease to the fingertip) elicits pain. Tenderness being limited to the sheath (not diffusely spread) helps localise the infection
2	Symmetrical enlargement of the digit ("fusiform")	Sensitive but less specific	Pus fills the sheath uniformly along its length → the finger swells symmetrically like a sausage/spindle. Other causes of sausage digit (dactylitis, cellulitis) reduce specificity
3	Severe pain on passive extension of the finger (greater proximally)	Most specific (~97%)	Passive extension stretches the inflamed, tense sheath and increases intra-sheath pressure. Pain is greater proximally because the proximal sheath is where pus tends to pool (gravity + anatomy of the cul-de-sac). This sign is rarely positive in non-sheath infections
4	Flexed posture of the involved digit	Moderately sensitive	The sheath accommodates maximal volume when the finger is in slight flexion (the sheath is lax). Extension would compress the sheath → the patient instinctively holds the finger flexed to minimise pain. Also contributed to by flexor spasm

How Many Kanavel Signs Do You Need?

The lecture slides present a clear threshold ^[1]:

1–2 Kanavel signs + mild clinical symptoms + early infection → Low clinical suspicion → Trial of non-operative management
3–4 Kanavel signs + moderate/severe symptoms → High clinical suspicion → Surgical emergency — proceed to operative treatment

In practice: if even 2 signs are present in the right clinical context (e.g., penetrating wound + immunocompromised), maintain a very low threshold for surgery. The signs may not all be present early in the disease course. The key principle is that prompt clinical diagnosis is essential ^[1] — waiting for all 4 signs to develop risks tendon necrosis.

Let's think about this from first principles:

The flexor tendon sheath is a tiny, deep structure — you cannot aspirate it reliably at the bedside (unlike a knee joint in septic arthritis)
Imaging (X-ray, ultrasound, MRI) can support the diagnosis but none are sensitive or specific enough to confirm or exclude PFT definitively in the acute setting
Blood tests (WCC, CRP) are non-specific — they tell you there is infection somewhere but not where
Microbiological confirmation (culture from sheath aspirate or intraoperative samples) comes after treatment has begun

Therefore, the clinical decision to operate is made before investigations return. Investigations serve to:

Support the clinical diagnosis
Exclude differentials (fracture, gout, foreign body)
Guide antibiotic therapy (culture & sensitivity)
Assess for complications (osteomyelitis, deep space infection)
Risk-stratify the patient (DM, renal failure, immunosuppression)

Exam Principle

Never delay surgical treatment of PFT while waiting for investigation results. Prompt clinical diagnosis ^[1] and treatment takes priority. Investigations are supportive, not gate-keeping.

The following algorithm integrates the clinical assessment with investigation findings and the management protocol flow chart from the lecture ^[1]:

Key Decision Points from Lecture

Non-operative treatment is indicated when: ^[1]

Early presentation, within 48 hours after injury
Antibiotics started
Examine the affected hand frequently
No improvement after 24 to 48 hours → surgery is indicated

This means non-operative management is only a monitored trial — you must reassess regularly and have a very low threshold to escalate to surgery.

3. Investigation Modalities

Investigations are organised into bedside, blood tests, imaging, and microbiological categories. For each, I'll explain what you're looking for, why it's relevant, and how to interpret the findings.

Investigation	What to Look For	Why / Interpretation
Vital signs	Fever (temperature > 38°C), tachycardia, hypotension	Systemic inflammatory response. Fever supports infective aetiology. Hypotension + tachycardia → concern for sepsis (especially if necrotizing fasciitis or horseshoe abscess)
Wound inspection	Site, size, depth of any puncture wound; foreign body; discharge	Identifies the portal of entry. Purulent discharge from the wound confirms infection. A retained foreign body (thorn, fish bone) may be visible or palpable
Capillary refill time and perfusion	Prolonged CRT, mottling, pallor of the digit	Vascular compromise — may indicate compartment-like pressure in the sheath, or concurrent peripheral vascular disease
Neurovascular status of the digit	Sensation (two-point discrimination), motor function, digital Allen's test	Baseline neurovascular assessment before surgery. Also assesses whether digital nerve/artery is compromised by swelling
Blood glucose (point-of-care)	Hyperglycaemia	Undiagnosed or poorly controlled DM — a major risk factor for poor outcomes and amputation ^[1]. Needs aggressive glycaemic control

Investigations include CBP, ESR, CRP ^[1] (discussed in the context of septic arthritis, but equally applicable to PFT):

Test	Expected Findings in PFT	Why / Interpretation
Complete blood picture (CBP)	Leucocytosis with neutrophilia (left shift)	Acute bacterial infection stimulates bone marrow neutrophil release. A normal WCC does not exclude PFT (can be normal early, or in immunosuppressed patients). A very high WCC ( > 15,000) with bandaemia suggests severe/systemic infection
Erythrocyte sedimentation rate (ESR)	Elevated (often > 30 mm/hr)	Non-specific marker of inflammation. Rises slowly (over days). More useful for monitoring treatment response over time than for acute diagnosis
C-reactive protein (CRP)	Elevated (often > 50 mg/L)	Acute phase reactant synthesised by the liver in response to IL-6. Rises within 6–8 hours of infection onset and peaks at 48 hours. More responsive than ESR for acute infection. Serial CRP is useful for monitoring treatment response — a falling CRP suggests improving infection
Blood cultures (aerobic + anaerobic)	May be positive (especially in bacteraemia/sepsis)	Should be taken before starting antibiotics. Positive in ~10–20% of PFT cases. More likely positive if systemically unwell. Identifies the organism and guides targeted antibiotic therapy. Blood for C/ST (50% positive in osteomyelitis) ^[4] — yield is lower in PFT but still important
Renal function (U&E, creatinine)	Elevated creatinine → renal failure is a risk factor for amputation ^[1]	Assesses comorbidity. Also needed for antibiotic dosing (many antibiotics are renally cleared). Acute kidney injury may indicate sepsis
Liver function tests	Deranged in liver disease / cirrhosis	Liver disease predisposes to Vibrio vulnificus infection — relevant in Hong Kong. Also affects drug metabolism
HbA1c	> 6.5% indicates diabetes	Identifies undiagnosed DM or assesses chronic glycaemic control in known diabetics. DM present in 57% of necrotizing fasciitis patients ^[1] — similarly important in PFT
Blood glucose	Hyperglycaemia	Acute stress response and/or uncontrolled DM
Uric acid + joint aspirate microscopy (if DDx gout)	Elevated uric acid; negatively birefringent crystals on polarised microscopy	To exclude crystal arthropathy as a differential. Remember: hyperuricaemia alone does not confirm gout — crystal identification is required
Procalcitonin (if available)	Elevated in bacterial infection	More specific for bacterial infection than CRP. Helps differentiate bacterial from non-bacterial inflammation. Not universally available

Interpreting Normal Bloods

A normal WCC and CRP do NOT exclude PFT, especially in:

Early infection (within first 24 hours — CRP hasn't peaked yet)
Immunosuppressed patients (unable to mount an adequate inflammatory response)
Elderly patients (blunted inflammatory response)

If the clinical picture fits (Kanavel signs present), treat the patient, not the blood test.

Describe the radiological features associated with MSS infections is a stated learning outcome ^[1].

Modality	What to Look For	Why / Interpretation
X-ray of the affected hand (AP and lateral)	Soft tissue swelling (fusiform along the digit); foreign body (radiopaque material — glass, metal, gravel); subcutaneous gas (suggests gas gangrene or necrotizing fasciitis); fracture (if trauma); periarticular osteopenia / joint space changes (if coexistent septic arthritis or osteomyelitis)	X-ray is the first-line imaging — fast, cheap, widely available. Its main role in PFT is to exclude other diagnoses (fracture, foreign body, gas gangrene) and detect complications (osteomyelitis). X-ray: normal in acute osteomyelitis ^[4] — so a normal X-ray does NOT exclude bony involvement. Linear streak of gas on X-ray suggests gas gangrene ^[4]. In septic arthritis: joint space effusion, periarticular osteopenia ^[4]
Ultrasound (USS) of the tendon sheath	Fluid within the tendon sheath (anechoic or hypoechoic collection surrounding the tendon); thickened synovial sheath; peritendinous oedema; foreign body (even non-radiopaque ones like wood, thorns)	USS is excellent for detecting fluid in the tendon sheath — a distended sheath with echogenic fluid (pus) is highly suggestive. It can also identify foreign bodies missed on X-ray. Limitations: operator-dependent, cannot differentiate sterile from infected fluid. Best used as a bedside adjunct to clinical examination. Can also guide aspiration of the sheath if attempted
MRI of the hand	Fluid signal within the tendon sheath (T2 hyperintense); synovial sheath enhancement (post-gadolinium); peritendinous oedema; adjacent soft tissue infection (deep space abscess); osteomyelitis (bone marrow oedema)	MRI: useful to detect any co-existent osteomyelitis — not routine ^[1]. MRI is the most sensitive and specific imaging modality for PFT and its complications. It beautifully shows the anatomical extent of infection — critical for surgical planning. However, it is time-consuming (30–60 minutes), expensive, and not available emergently in most centres. Therefore, it is reserved for: (a) diagnostic uncertainty, (b) suspected complications (osteomyelitis, deep space infection), (c) chronic/atypical presentations (M. marinum). Do NOT delay surgery to obtain an MRI
CT scan	Soft tissue collections, gas, bony involvement	Less useful than MRI for soft tissue detail. May be used if MRI is unavailable or to look for gas in deep tissues (necrotizing fasciitis). CT with contrast for deep/organ space infection: rim-enhancing collection ^[5]

Summary of Imaging Hierarchy in PFT:

X-ray → first line (exclude fracture, foreign body, gas)

Ultrasound → bedside adjunct (detect sheath fluid, foreign body)

MRI → gold standard for soft tissue detail but NOT routine and NOT for acute decision-making

CT → rarely needed; consider if necrotizing fasciitis suspected

3.4 Microbiological Investigations

These are the investigations that guide targeted antibiotic therapy. Think of them in two stages: pre-operative and intra-operative.

Sample	Tests Ordered	Interpretation
Wound swab / pus from the entry wound	Gram stain, culture and sensitivity (C/ST), AFB smear (if chronic/atypical)	Wound swab/pus for culture ^[5] — take from the wound itself, avoid the wound edge (contamination with skin flora) ^[5]. Gram stain gives a rapid (< 1 hour) guide to organism morphology (Gram-positive cocci in clusters → Staph; Gram-positive cocci in chains → Strep; Gram-negative rods → enteric organisms). Culture and sensitivity takes 24–48 hours but gives definitive identification and antibiogram
Blood cultures (x2 sets, aerobic + anaerobic)	C/ST	Take before starting antibiotics. Two sets from different venepuncture sites to reduce contamination. Positive in ~10–20% of PFT; higher yield if systemically septic
Swabs for specific pathogens (if clinically indicated)	Gonococcal NAAT (genital/rectal/pharyngeal); AFB smear and Mycobacterium culture (if chronic/marine exposure)	If DGI suspected: NAAT more sensitive than culture. If M. marinum suspected: warn the lab — requires prolonged incubation at 30–32°C (lower than standard 37°C), otherwise will be missed

Sample	Tests Ordered	Interpretation
Sheath fluid / pus aspirate	Gram stain, C/ST (aerobic + anaerobic + fungal), AFB smear and culture	This is the most important microbiological sample — direct from the site of infection, highest yield. Gram stain guides initial empirical therapy refinement
Tissue biopsy (synovial sheath wall)	Histopathology (H&E, Ziehl-Neelsen, PAS/GMS for fungi), tissue culture (bacterial, mycobacterial, fungal)	Essential if chronic/granulomatous infection suspected (M. marinum, TB, fungal). Histopathology shows granulomatous inflammation with caseation (TB) or non-caseating granulomas (M. marinum). Tissue culture is more sensitive than swab culture for atypical mycobacteria
Foreign body (if found)	Send for culture	A retained foreign body (thorn, fish bone) may harbour organisms

Lab Communication for Atypical Organisms

If you suspect Mycobacterium marinum (marine injury, chronic indolent course), you must explicitly communicate this to the microbiology lab. Standard culture protocols incubate at 37°C, but M. marinum grows optimally at 30–32°C and requires prolonged incubation (up to 6–8 weeks). If you don't alert the lab, the culture will be falsely reported as negative.

Similarly, for Neisseria gonorrhoeae, request specific chocolate agar or NAAT — the organism is fastidious and will not grow on routine media.

Differential Being Considered	Additional Investigation	Key Finding
Septic arthritis	Joint aspiration: Gram stain, culture, crystal, glucose ^[1]	WCC > 50,000/mm³, > 75% PMN, positive Gram stain (60–80%) for bacterial (non-gonococcal) septic arthritis ^[1]. Low glucose ( < 50% of serum glucose)
Gout / pseudogout	Joint aspirate with polarised microscopy	Negatively birefringent needle-shaped crystals (monosodium urate = gout); positively birefringent rhomboid crystals (calcium pyrophosphate = pseudogout)
Necrotizing fasciitis	LRINEC score ^[4]; bedside finger probe test ^[1]	LRINEC > 8 = high risk ^[4]. Components: CRP, Hb, WCC, sodium, creatinine, glucose. Finger probe test: lack of bleeding, foul smelling dishwater pus, minimal tissue resistance to finger dissection ^[1]
Osteomyelitis	X-ray (may be normal acutely); MRI: best in diagnosis ^[4]	X-ray: periosteal reaction, sclerosis in chronic; normal in acute ^[4]. MRI: bone marrow oedema, periosteal enhancement
Foreign body	X-ray (radiopaque); USS (non-radiopaque)	Radiopaque on X-ray: metal, glass. Non-radiopaque on USS: wood, thorn, plastic — appear as hyperechoic foci with posterior acoustic shadowing
Fracture	X-ray hand (AP + lateral + oblique)	Fracture line, cortical discontinuity, displacement
Herpetic whitlow	Viral PCR / Tzanck smear	Multinucleated giant cells on Tzanck; HSV PCR positive

When you receive investigation results, interpret them in the context of the clinical picture:

Scenario	Bloods	X-ray	USS	Clinical	Interpretation
Classic acute PFT	WCC ↑, CRP ↑	Soft tissue swelling, no fracture	Fluid in tendon sheath	3–4 Kanavel signs	Confirmed PFT → emergency surgery
Early PFT	Normal or mildly ↑	Normal or mild soft tissue swelling	May show early fluid	1–2 Kanavel signs	Possible early PFT → antibiotics + close monitoring
PFT with osteomyelitis	WCC ↑↑, CRP ↑↑, ESR ↑↑	Periosteal reaction (if chronic)	Fluid in sheath + periosteal changes	Severe, late presentation	Complicated PFT → open debridement + prolonged antibiotics
Chronic granulomatous	WCC normal, ESR mildly ↑	Normal or lytic bone changes	Thickened sheath, complex fluid	Indolent sausage digit, marine exposure	Suspect M. marinum → tissue biopsy + special cultures
Necrotizing fasciitis	WCC ↑↑, CRP ↑↑↑, Na ↓, Cr ↑	Gas in soft tissues	Deep fluid, fascial oedema	Pain out of proportion, haemorrhagic bullae, systemic toxicity ^[1] ^[4]	Emergency → aggressive debridement

Category	Investigation	Primary Purpose	Timing
Bedside	Vital signs, BSL, neurovascular exam	Assess systemic status, risk-stratify	Immediate
Bloods	CBP, ESR, CRP ^[1]	Confirm systemic inflammation	Immediate — do NOT delay treatment
Bloods	Blood cultures (x2 sets)	Identify organism for targeted Abx	Before starting antibiotics
Bloods	U&E, Cr, LFT, HbA1c, glucose	Assess comorbidities, Abx dosing	Immediate
Imaging	X-ray hand (AP + lateral)	Exclude fracture, foreign body, gas	First-line, immediate
Imaging	USS tendon sheath	Detect sheath fluid, foreign body	Bedside adjunct
Imaging	MRI (not routine ^[1])	Detect osteomyelitis, deep space infection	If diagnostic uncertainty or complications suspected
Microbiology	Wound swab / pus for C/ST	Identify organism	Pre-operative
Microbiology	Intra-op sheath fluid + tissue biopsy	Gold standard microbiological sample	During surgery
Special	Joint aspirate (if DDx septic arthritis)	Gram stain, culture, crystal, glucose ^[1]	If joint involvement suspected

High Yield Summary

Diagnosis of PFT — Key Takeaways:

PFT is a CLINICAL diagnosis based on Kanavel's 4 cardinal signs ^[1] — no investigation can replace bedside assessment
Most sensitive sign: tenderness along the entire flexor sheath; Most specific sign: pain on passive extension
Threshold for surgery: 3–4 Kanavel signs → surgical emergency; 1–2 signs → trial of antibiotics with reassessment at 24 hours ^[1]
Investigations are supportive, not gate-keeping — prompt clinical diagnosis ^[1] takes priority
First-line imaging: X-ray (exclude fracture, foreign body, gas); USS (detect sheath fluid); MRI is not routine but best for complications ^[1]
Bloods: CBP, ESR, CRP ^[1] + blood cultures before antibiotics + renal function + glucose/HbA1c
Gold standard microbiology: intra-operative sheath fluid and tissue biopsy sent for Gram stain, C/ST (aerobic, anaerobic, AFB, fungal)
Alert the lab if you suspect M. marinum (30–32°C incubation) or N. gonorrhoeae (chocolate agar / NAAT)
Normal bloods do NOT exclude PFT — treat the patient, not the blood test

Active Recall - Dx Criteria, Algorithm and Investigations for PFT

References

^[1] Lecture slides: GC 237. Musculoskeletal infection [Updated in 2025] (1).pdf (pages 2, 3, 19, 21, 24, 27, 28, 29, 32, 54) ^[4] Senior notes: maxim.md (sections 565–567: osteomyelitis, septic arthritis, necrotizing fasciitis, gas gangrene, LRINEC score) ^[5] Senior notes: maxim.md (section 59: surgical site infection — wound swab for culture, CT with contrast for deep infection)

Management of Infective (Pyogenic Flexor) Tenosynovitis

The management of PFT follows a simple logic chain derived from its pathophysiology: bacteria in a closed space → pus → rising pressure → tendon death. Therefore, the goals of treatment are:

Kill the bacteria → antibiotics
Decompress the closed space / drain the pus → surgical irrigation and debridement
Prevent further damage → splinting, elevation, wound care
Optimise the host → control comorbidities (DM, renal failure)
Restore function → rehabilitation

Management ^[1]:

Prompt clinical diagnosis
Empirical antibiotics covering Staphylococcus and Streptococcus species
Antibiotics should cover gram-negative rods and anaerobes in case of immunocompromised patients
Non-operative treatment
Operative treatment

Empirical antibiotics and early surgical intervention are necessary in case of life-threatening conditions such as septic arthritis, NF and gas gangrene ^[1] — the same urgency applies to PFT.

The management protocol flow chart ^[1] stratifies patients by clinical suspicion:

3. Treatment Modalities — Detailed Breakdown

These form the foundation of management, applied to all patients regardless of operative vs non-operative pathway:

Measure	Rationale (First Principles)	Details
Hand elevation	Elevation above heart level reduces hydrostatic capillary pressure (Starling forces) → decreases oedema formation → lowers intra-sheath pressure → reduces pain and may slow vascular compromise of the tendon	Use a Bradford sling or pillow elevation. The hand should be kept elevated at all times except during examination/treatment
Splinting	Immobilisation in the "position of safety" (wrist in ~20° extension, MCPJs in ~70° flexion, IPJs in slight flexion) reduces movement-related pain, prevents tendon adhesion in a maximally shortened position, and allows the inflammatory process to settle	A volar forearm-based splint is typically used. The "position of safety" is chosen because it keeps the collateral ligaments of the MCPJ and PIPJ at maximal stretch (preventing contracture), while keeping the hand in a functional position
Analgesia	Pain control is essential — PFT is excruciatingly painful. Uncontrolled pain also causes sympathetic activation → vasoconstriction → worsens perfusion	Paracetamol + NSAIDs (if not contraindicated) ± opioids for severe pain. Avoid NSAIDs in necrotizing fasciitis as they may mask symptoms and contribute to renal failure ^[1] — but in uncomplicated PFT, they are generally safe
Tetanus prophylaxis	PFT typically follows penetrating trauma → risk of Clostridium tetani inoculation	Check tetanus vaccination status. Give tetanus toxoid booster (or TIG + toxoid if unvaccinated/unknown status) per wound management guidelines
Optimise comorbidities	DM, renal failure, peripheral vascular disease are risk factors for amputation ^[1]. Poor glycaemic control impairs neutrophil function, delays wound healing, and increases infection severity	Tight glycaemic control (target BSL 6–10 mmol/L in acute setting), manage renal failure (avoid nephrotoxic drugs, adjust antibiotic doses), optimise nutrition
Nil by mouth	If surgery is anticipated, the patient must be fasted	NBM in case emergency theatre is needed

3.2 Antibiotic Therapy

Antibiotics are the pharmacological cornerstone. Think of them in two phases: empirical (started immediately, before cultures return) and targeted (adjusted once culture and sensitivity results are available).

Empirical antibiotics covering Staphylococcus and Streptococcus species ^[1]. Antibiotics should cover gram-negative rods and anaerobes in case of immunocompromised patients ^[1].

Patient Group	Recommended Empirical Regimen	Why This Covers the Likely Organisms
Immunocompetent, standard presentation	IV cloxacillin (or flucloxacillin) 1–2g Q6H ± IV penicillin (or ampicillin)	Cloxacillin (clox = "anti-staphylococcal penicillin") targets S. aureus (MSSA — the most common organism). Penicillin covers Streptococcus spp. Cloxacillin is penicillinase-resistant, meaning it withstands the β-lactamase that S. aureus produces. IV cloxacillin is the standard for MSS infections ^[4]
MRSA suspected (healthcare-associated, IV drug user, prior MRSA)	IV vancomycin (trough-guided dosing)	Vancomycin is a glycopeptide that inhibits cell wall synthesis by binding D-Ala-D-Ala; active against MRSA because it bypasses the altered PBP mechanism
Immunocompromised (DM, renal failure, liver disease, HIV)	IV piperacillin-tazobactam (Tazocin) or IV ampicillin-sulbactam (Unasyn) OR IV cefuroxime + IV metronidazole	Must cover gram-negative rods and anaerobes ^[1]. Piperacillin-tazobactam is a broad-spectrum β-lactam/β-lactamase inhibitor combination covering Gram-positives + Gram-negatives + anaerobes. Metronidazole (metro = "against" + nidazole = nitroimidazole) specifically targets anaerobes via DNA damage in anaerobic conditions
Human/animal bite wound	IV amoxicillin-clavulanate (Augmentin) or IV ampicillin-sulbactam	Covers oral flora: Pasteurella multocida (cat/dog), Eikenella corrodens (human), plus anaerobes. Clavulanate/sulbactam provides β-lactamase inhibition
Marine injury (fish bone, seafood handling — Hong Kong relevant)	Add IV doxycycline or ciprofloxacin to standard regimen	To cover Vibrio vulnificus and Vibrio spp. Doxycycline is a tetracycline that inhibits the 30S ribosomal subunit. In patients with liver disease + Vibrio, the mortality is extremely high without prompt coverage
Suspected Neisseria gonorrhoeae (DGI)	IV ceftriaxone 1g daily	NG: IV ceftriaxone × 1 week ^[4]. Ceftriaxone is a 3rd-generation cephalosporin with excellent Gram-negative coverage and good CNS/joint penetration
Suspected Mycobacterium marinum (chronic, indolent, marine exposure)	Rifampicin + ethambutol or clarithromycin + ethambutol for 3–6 months	M. marinum is an atypical mycobacterium resistant to standard antibiotics. Rifampicin inhibits RNA polymerase; ethambutol inhibits arabinosyl transferase (cell wall synthesis); clarithromycin inhibits the 50S ribosomal subunit. Prolonged treatment is necessary due to slow mycobacterial growth

Route and Duration

Route: Always start with IV antibiotics in PFT — the tendon sheath has poor blood supply, so high serum drug levels are needed to achieve adequate tissue penetration. Oral antibiotics alone are insufficient for established PFT.
Duration: Typically IV for 1–2 weeks, then step-down to oral antibiotics once clinical improvement is evident (settling Kanavel signs, falling CRP, afebrile for 48h). Total duration is usually 2–4 weeks for uncomplicated PFT, but may be 4–6 weeks if complicated by osteomyelitis (IV cloxacillin × 4–6 weeks for osteomyelitis/septic arthritis) ^[4].
Switch to targeted therapy as soon as culture and sensitivity results are available (usually 48–72 hours).

3.3 Non-Operative Treatment

Non-operative treatment ^[1]:

Indicated when early presentation, within 48 hours after injury
Antibiotic
Examine the affected hand frequently
No improvement after 24 to 48 hours, surgery is indicated

Criterion	Rationale
Early presentation (within 48 hours after injury) ^[1]	The earlier the infection is caught, the less pus has accumulated and the less tendon damage has occurred. Very early infection may be in a "pre-suppurative" (cellulitic) phase where antibiotics alone can abort the infection
1–2 Kanavel signs only, mild clinical symptoms ^[1]	Fewer Kanavel signs suggest a lower bacterial burden and less intra-sheath pressure. The sheath may not yet be fully distended with pus
Immunocompetent host	An intact immune system can assist antibiotics in clearing a low-burden infection
No systemic toxicity	Absence of sepsis/SIRS suggests the infection is localised and less severe

Admit the patient (this is NOT outpatient management)
IV empirical antibiotics as above
Hand elevation + splint in position of safety
Analgesia
Examine the affected hand frequently ^[1] — at least Q4–6 hourly, documenting:
- Number of Kanavel signs
- Extent of swelling and erythema
- Pain level
- Temperature
- Neurovascular status of the digit
Reassess at 24 hours ^[1]:
- Improving (fewer Kanavel signs, less pain, settling swelling, falling CRP) → continued non-surgical treatment ^[1], complete antibiotic course
- No improvement after 24 to 48 hours → surgery is indicated ^[1]

Critical Safety Net

Non-operative management is a monitored trial, not definitive treatment. The patient must be admitted, examined frequently, and have a pre-arranged plan for surgical escalation. If there is any doubt about whether the patient is improving, err on the side of surgery. A "negative" exploration of the tendon sheath (washing out a sheath that turns out to have less pus than expected) is far safer than a delayed exploration of a sheath containing necrotic tendon.

Contraindication	Reason
3–4 Kanavel signs	Established infection — antibiotics alone are insufficient to clear pus from a closed space
Late presentation ( > 48 hours)	More pus, more tendon damage, higher bacterial burden
Immunocompromised patient	Reduced ability to clear infection; higher risk of rapid progression
Systemic sepsis	Indicates high bacterial burden; source control (drainage) is essential
Evidence of complications (abscess, necrosis, horseshoe abscess, osteomyelitis)	Cannot be managed without surgical intervention
Failure to improve at 24 hours	The trial period has expired — escalate to surgery

3.4 Operative Treatment

Operative treatment ^[1] is the definitive management for established PFT. There are two main surgical approaches:

Closed catheter irrigation and debridement ^[1] — the technique originally described by Neviaser in 1978.

Principle: Two small incisions are made at either end of the tendon sheath, and a catheter is passed through the sheath. Sterile saline is then continuously or intermittently irrigated through the catheter to flush out pus and bacteria, while preserving the sheath integrity.

Aspect	Detail
Incisions	Two small transverse or midlateral incisions: one proximal (at the level of the A1 pulley / distal palmar crease) and one distal (at the level of the A5 pulley / DIP crease)
Catheter	A small paediatric feeding tube or angiocatheter is threaded through the sheath from proximal to distal
Irrigation	Sterile normal saline (NOT antiseptic solutions — they are cytotoxic to healthy tissue). Continuous or intermittent irrigation for 24–48 hours post-operatively
Samples	Sheath fluid sent for Gram stain, C/ST (aerobic + anaerobic + AFB + fungal)
Wound	Incisions left open or loosely approximated to allow continued drainage

Indications:

High clinical suspicion (3–4 Kanavel signs, moderate/severe symptoms) ^[1] without evidence of advanced infection, necrosis, or chronic infection
Failed non-operative treatment (no improvement at 24 hours)
Relatively early presentation with established but non-advanced infection

Advantages:

Minimally invasive
Preserves the tendon sheath (important for future tendon gliding and function)
Can be done under regional anaesthesia (wrist block or digital block — though general anaesthesia is often used)

Contraindications / When to proceed to open approach:

Presence of advanced infection, necrosis, chronic infection ^[1]
Thick organised pus that will not flush out via catheter
Concurrent deep space infection requiring open drainage
Horseshoe abscess (need to explore the radial/ulnar bursae and space of Parona)

Open irrigation and debridement ^[1] — for advanced or complicated infections.

Aspect	Detail
Incision	Zig-zag incision ^[1] (Bruner incision) along the volar surface of the digit and palm. The zig-zag pattern crosses the flexion creases at an angle, which prevents contracture of the scar across the crease (a straight incision across a flexion crease would contract and cause a flexion contracture)
Exposure	The flexor tendon sheath is fully exposed. The A3, A5, and cruciate pulleys can be opened/excised to access the sheath lumen, but the A2 and A4 pulleys must be preserved (they are biomechanically critical for preventing bowstringing)
Debridement	Necrotic tendon, necrotic synovium, and organised pus are debrided. Viable tendon and pulleys are preserved
Irrigation	Copious irrigation with sterile normal saline (litres)
Samples	Sheath fluid, tissue biopsies (synovium, necrotic tissue), foreign bodies → all sent for Gram stain, C/ST, histopathology, AFB
Wound	Left open (not closed primarily) for secondary intention healing or delayed primary closure. Daily wound care and dressing changes
Extended exploration	If horseshoe abscess: extend incision to explore the palm (midpalmar space, thenar space) and the forearm (space of Parona via a separate incision over the distal volar forearm). If osteomyelitis: debride affected bone

Indications ^[1]:

Presence of advanced infection, necrosis, chronic infection ^[1]
Failed closed catheter irrigation
Horseshoe abscess (thumb/little finger with proximal extension)
Deep space infection (midpalmar, thenar, forearm)
Concurrent osteomyelitis requiring bone debridement
Retained foreign body requiring extraction
Necrotic tendon requiring excision

Contraindications:

There are no absolute contraindications to open debridement when it is indicated — the principle of "life over limb" applies. Even in patients too unwell for general anaesthesia, regional anaesthesia (brachial plexus block) can be used
Relative: a patient who is too systemically unstable for any surgery may need initial resuscitation/stabilisation (e.g., in septic shock) before theatre — but this is a matter of timing, not a contraindication to surgery itself

Zig-Zag (Bruner) Incision — Why?

The zig-zag incision ^[1] is not arbitrary. A straight longitudinal incision along the volar finger would cross the flexion creases of the PIPJ and DIPJ at right angles. As the wound heals by secondary intention (since it is left open), the scar contracts. A scar that crosses a flexion crease at 90° pulls the joint into flexion → flexion contracture. The zig-zag pattern ensures that no scar crosses a crease perpendicularly, distributing tension across multiple planes and preventing contracture. This is the same principle used in Dupuytren's fasciectomy incisions.

Feature	Closed Catheter Irrigation	Open Irrigation and Debridement
Invasiveness	Less invasive	More invasive
Sheath preservation	Preserves sheath	May require partial opening of sheath
Indication	Moderate/established infection without necrosis	Advanced infection, necrosis, chronic infection ^[1]
Visualisation	Limited (cannot directly inspect tendon)	Complete (direct visualisation of tendon, sheath, pulleys)
Debridement	Irrigation only (cannot mechanically debride)	Full mechanical + irrigation debridement
Post-op drainage	Via catheter irrigation	Via open wound
Recovery	Faster	Slower (open wound healing)
Risk of tendon adhesion	Lower (sheath preserved)	Higher (sheath opened, more surgical trauma)
Failure rate	Higher (may need repeat or conversion to open)	Lower (definitive)

Component	Details	Rationale
Continued IV antibiotics	As per empirical regimen, then tailored to culture results	Continue killing bacteria; the surgical drainage alone does not sterilise the field
Catheter irrigation (if closed technique)	Continuous or intermittent saline irrigation for 24–48 hours, then catheter removal	Ongoing lavage flushes residual bacteria and inflammatory debris
Wound care	Daily dressing changes under aseptic technique; wounds left open for secondary intention or delayed primary closure at 48–72 hours if clean	Allows ongoing drainage and inspection; reduces risk of re-accumulating pus
Hand elevation	Continue until swelling subsides	Reduces oedema
Splinting	Position of safety splint between therapy sessions	Prevents contracture in a functional position
Re-examination at 48 hours	Assess clinical response: Kanavel signs resolving? CRP falling? Afebrile?	If not improving → return to theatre for repeat washout or escalation to open debridement
IV-to-oral antibiotic switch	When: afebrile for 48h, CRP trending down, clinically improving, tolerating oral intake	Oral antibiotics achieve lower tissue levels but are adequate once the bacterial burden has been substantially reduced by surgery + IV therapy
Rehabilitation	Early active/passive ROM exercises under hand therapist guidance, starting once infection is controlled (usually 48–72h post-op)	Tendon adhesions form rapidly after any tendon sheath surgery/infection. Early movement promotes tendon gliding and prevents stiffness. This is a balance: too early risks disrupting healing; too late results in a stiff, non-functional finger

3.6 Special Situations

Risk factors for amputation ^[1]:

DM
Renal failure
Peripheral vascular disease

Indications for amputation:

Completely necrotic tendon with non-viable digit (no perfusion despite debridement)
Overwhelming infection with digital gangrene
Life-threatening sepsis where the digit is the source and cannot be salvaged
A functionless, painful finger after multiple failed debridements

Amputation is a last resort. The decision should be made by a senior hand surgeon and discussed with the patient.

Extended antibiotic therapy: rifampicin + ethambutol (or clarithromycin + ethambutol) for 3–6 months minimum
Surgical synovectomy: debridement of granulomatous tissue; send tissue for AFB culture at 30–32°C and histopathology
No role for standard short-course antibiotics

Requires extensive open debridement via:
- Zig-zag incision along the thumb
- Zig-zag incision along the little finger
- Separate incision over the distal volar forearm (to drain the space of Parona)
Multiple drains and staged debridements often required
Worst functional outcomes of all PFT presentations

Scenario	Treatment	Key Points
Early PFT, 1–2 Kanavel signs, < 48h	Non-surgical: IV antibiotics + elevation + splint + frequent examination ^[1]	Reassess at 24h; no improvement → surgery
Established PFT, 3–4 Kanavel signs, no necrosis	Surgical: Closed catheter irrigation + empiric antibiotics ^[1]	Preserve tendon sheath; send intra-op cultures
Advanced PFT, necrosis, or chronic infection	Surgical: Open irrigation and debridement + empiric antibiotics ^[1]	Zig-zag incision ^[1]; preserve A2/A4 pulleys
Horseshoe abscess	Extensive open debridement of thumb, little finger, palm, and forearm	Multiple incisions, staged procedures
Immunocompromised	Lower threshold for surgery; broad-spectrum antibiotics covering Gram-negatives + anaerobes ^[1]	Aggressive approach, close monitoring
M. marinum	Surgical synovectomy + prolonged antibiotics (3–6 months)	Alert lab to incubate at 30–32°C
Non-salvageable digit	Amputation	Last resort; discuss with patient

High Yield Summary

Management of PFT — Key Takeaways:

Prompt clinical diagnosis is the first and most important step ^[1]
Empirical antibiotics: cover Staph + Strep (IV cloxacillin); add Gram-negative and anaerobic cover in immunocompromised ^[1]
Non-operative treatment: early presentation within 48 hours, 1–2 Kanavel signs, mild symptoms → IV antibiotics + elevation + splinting + frequent examination → no improvement after 24–48 hours → surgery ^[1]
Operative treatment:
- Closed catheter irrigation: for moderate/established infection without necrosis ^[1]
- Open irrigation and debridement (zig-zag incision): for advanced infection, necrosis, chronic infection ^[1]
Post-operative: continued IV antibiotics tailored to cultures, wound care, elevation, splinting, early rehabilitation
Risk factors for amputation: DM, renal failure, peripheral vascular disease ^[1]
Always preserve A2 and A4 pulleys during open surgery to prevent bowstringing
Zig-zag incision prevents flexion contracture by avoiding perpendicular scars across flexion creases

Active Recall - Management of Infective Tenosynovitis

References

^[1] Lecture slides: GC 237. Musculoskeletal infection [Updated in 2025] (1).pdf (pages 2, 3, 24, 28, 29, 30, 32, 33, 54) ^[4] Senior notes: maxim.md (sections 566–567: osteomyelitis, septic arthritis — IV cloxacillin regimens, ceftriaxone for NG)

Complications of Infective (Pyogenic Flexor) Tenosynovitis

Understand the sequelae of MSS infections if not treated promptly is a stated learning outcome ^[1]. Complications of PFT arise from two fundamental pathological processes:

The infection itself — tissue destruction by bacteria, pus, and the host inflammatory response within a closed space
The treatment — surgical complications and antibiotic side effects

The severity of complications is directly proportional to the duration of untreated infection and the host's immune reserve. This is why the entire preceding management framework emphasises speed: prompt clinical diagnosis ^[1] and early surgical intervention ^[1] are the best ways to prevent complications.

1. Local Complications (Within the Digit and Hand)

Aspect	Explanation
Mechanism	This is the feared complication that makes PFT a surgical emergency. Pus accumulates within the non-distensible tendon sheath → intra-sheath pressure rises → compression of the vincula (the mesenteric-like folds carrying blood vessels from the digital arteries to the tendon surface) → tendon ischaemia. If pressure is not relieved within ~24–48 hours, the tendon undergoes irreversible coagulative necrosis. The necrotic tendon subsequently weakens and ruptures. This is identical in principle to how compartment syndrome kills muscle ^[6]
Clinical consequence	Loss of active flexion at the DIP (if FDP necroses) and/or PIP (if FDS necroses). A finger that cannot flex is functionally useless for grip. If both tendons necrose, the finger is essentially non-functional
Management	Prevention is key — early decompression. Once necrosed, the dead tendon must be debrided at surgery. Reconstruction with tendon grafting (e.g., palmaris longus graft) may be attempted later (usually staged, months after infection clearance), but outcomes are poor due to the scarred sheath bed

Aspect	Explanation
Mechanism	Even when the tendon survives, the inflammatory process within the sheath deposits fibrin → organisation into fibrous adhesions between the tendon surface and the sheath wall. These adhesions tether the tendon, preventing normal gliding. Additionally, prolonged immobilisation (splinting during treatment) allows the collateral ligaments of the PIPJ and DIPJ to shorten. Adhesions are a late complication ^[6] that contributes to a stiff, non-functional finger
Clinical consequence	Restricted active and passive ROM of the PIPJ and DIPJ. The finger may be locked in a fixed flexion deformity (analogous to Green's Grade IV trigger finger ^[2])
Management	Prevention: early post-operative rehabilitation (active/passive ROM exercises under hand therapy guidance, starting 48–72h post-op). Treatment: tenolysis (surgical release of adhesions) — but this is a secondary procedure performed only after the infection has completely resolved and the tissues have matured (~3–6 months later)

Aspect	Explanation
Mechanism	Prolonged inflammation → fibrous tissue formation within and around the sheath → shortening of the volar plate and collateral ligaments of the PIPJ → the joint becomes fixed in flexion. If open debridement was performed with a wound left to heal by secondary intention, scar contracture across the flexion crease worsens this (hence the importance of the zig-zag incision ^[1] to minimise perpendicular scar formation across creases)
Clinical consequence	Fixed flexion deformity — the finger cannot be fully extended. This impairs hand function for flat-surface tasks, glove wearing, and aesthetics
Management	Prevention: splinting in the position of safety, early ROM exercises. Treatment: serial splinting, physiotherapy, and if refractory, surgical release (capsulotomy ± tenolysis)

Why Stiffness Is So Common After PFT

The tendon sheath is a precision-engineered gliding mechanism — synovial fluid lubricates the tendon-sheath interface, and the pulleys guide the tendon at exact distances from the bone. Any disruption to this system (inflammation, adhesions, sheath damage during surgery, immobilisation) causes stiffness. This is why the balance between adequate treatment (which disrupts the sheath) and minimal surgical trauma (preserving the sheath) is so important, and why early rehabilitation is mandatory.

Aspect	Explanation
Mechanism	The digital neurovascular bundles run immediately adjacent to the tendon sheath on both sides of the finger. They can be damaged by: (a) the infection itself (inflammatory compression or direct bacterial destruction), (b) surgical manipulation during debridement (iatrogenic injury)
Clinical consequence	Nerve damage: numbness or dysaesthesia in the distribution of the affected digital nerve (one side of the finger distal to the injury). Artery damage: digital ischaemia (rare, as there are two digital arteries per finger providing collateral supply)
Management	Meticulous surgical technique with direct visualisation of neurovascular bundles during open debridement. If nerve transection occurs, microsurgical repair or nerve grafting may be attempted

2. Regional Complications (Spread Beyond the Digit)

Aspect	Explanation
Mechanism	Infection in the thumb sheath (continuous with the radial bursa) or little finger sheath (continuous with the ulnar bursa) tracks proximally through the bursa → across the space of Parona (potential space deep to pronator quadratus in the distal forearm) → into the other bursa → infects the other digit. This creates a "horseshoe" or "U-shaped" pattern of infection connecting the thumb and little finger via the forearm
Clinical consequence	Both the thumb AND little finger become infected, plus there is a deep collection in the distal forearm. Massive tissue destruction affecting multiple tendons. This is a devastating complication with very poor functional outcomes
Management	Extensive open debridement via multiple incisions (thumb, little finger, palm, and forearm). Staged debridements are often required. Prolonged IV antibiotics

Space	Anatomical Location	How PFT Spreads to It
Midpalmar space	Between the 3rd–5th metacarpals and the palmar aponeurosis	Direct extension from the ring/middle/little finger flexor sheath through the proximal cul-de-sac
Thenar space	Between the 1st metacarpal and the adductor pollicis	Extension from the index finger or thumb flexor sheath
Hypothenar space	Deep to the hypothenar muscles	Extension from the little finger sheath
Web spaces	Between the fingers at the metacarpal heads	Contiguous spread from adjacent digital sheaths

Deep space infections present with loss of the normal palmar concavity (the palm becomes "full" and convex due to the deep collection), severe pain, and systemic toxicity. They require open drainage through dedicated incisions.

Aspect	Explanation
Mechanism	The flexor tendon sheath is intimately related to the MCPJ, PIPJ, and DIPJ. Infection can erode through the sheath wall into the joint capsule, or spread via shared vascular channels. In infants (where the growth plate does not act as a barrier), and in adults where the sheath overlies the joint, contiguous spread is common
Clinical consequence	Joint cartilage destruction → chronic pain, stiffness, and eventually secondary osteoarthritis. Septic arthritis is one of the musculoskeletal infections you cannot miss ^[1] because of irreversible cartilage damage
Management	Joint aspiration for Gram stain, C/ST, crystal, glucose ^[1]; operative irrigation ^[4]; IV cloxacillin × 4–6 weeks ^[4]

Aspect	Explanation
Mechanism	Contiguous spread from the infected tendon sheath to the underlying phalanx. Bacteria penetrate the periosteum and enter the bone → suppuration → rising intraosseous pressure → spread through Volkmann canals to the bone surface → sequestrum (dead bone), involucrum (new reactive bone), cloacae (periosteal drainage openings) ^[4]
Clinical consequence	Chronic, difficult-to-eradicate bone infection. Draining sinuses. The necrotic bone (sequestrum) acts as a foreign body harbouring bacteria, making eradication without surgical debridement nearly impossible
Management	MRI: best in diagnosis ^[4]. IV cloxacillin × 4–6 weeks + surgical debridement ^[4]. May require bone resection if extensive

3. Systemic Complications

Aspect	Explanation
Mechanism	Bacteria from the infected sheath enter the bloodstream (bacteraemia) → systemic inflammatory response → organ dysfunction (sepsis) → if untreated, vasodilatory shock (septic shock). Risk is highest in immunocompromised patients and those with delayed treatment
Clinical consequence	Multi-organ failure, ICU admission, death
Management	Sepsis 6 bundle: blood cultures, serum lactate, IV antibiotics, IV fluids, urine output monitoring, oxygen. Source control (surgery) is mandatory

Aspect	Explanation
Mechanism	If the infection breaks through the tendon sheath and fascia, it may evolve into necrotizing fasciitis — a rapidly progressive, life-threatening soft tissue infection that destroys the fascial planes. This is more likely in immunocompromised patients, those with DM, and infections caused by S. pyogenes, V. vulnificus, or polymicrobial flora ^[1] ^[4]
Clinical consequence	Pain out of proportion to clinical signs, haemorrhagic bullae, systemic toxicity, dirty "dishwater" discharge ^[4]. If hand/forearm is involved, very high risk of limb loss
Management	Aggressive debridement + IV broad-spectrum antibiotics ^[4]. LRINEC score > 8 = high risk ^[4]

This is the ultimate local complication — loss of the digit or part of the hand.

Sequelae if not treated promptly ^[1]:

Amputation
HK figure: radical debridements (amputations and disarticulations) were performed in 46% of 24 patients
Mortality ranges from 20 to 75%

These HK data (from Tang WM et al., JBJS 2001, cited in the lecture ^[1]) refer specifically to necrotizing fasciitis of the hand, but they underscore the devastating potential of untreated or under-treated hand infections including PFT.

Aspect	Explanation
Mechanism	Tendon necrosis + digital artery thrombosis (due to peri-sheath inflammation) → non-viable, gangrenous digit. Or, overwhelming infection with sepsis where the digit is the source and cannot be salvaged
Risk factors for amputation ^[1]	DM — microangiopathy impairs perfusion and wound healing; Renal failure — uraemic immunosuppression; Peripheral vascular disease — inadequate perfusion for healing
Indications for amputation	Non-viable digit (gangrene, complete tendon necrosis, absent digital perfusion); uncontrollable infection despite multiple debridements; life-threatening sepsis requiring source control; functionless painful digit (elective, after infection resolved). Indications follow the 3D mnemonic ^[6]: Dead (ischaemia/gangrene), Damage (irreparable trauma), Danger (gangrene, ascending sepsis, necrotizing fasciitis, osteomyelitis)
Complications of amputation	Early: bleeding/haematoma, wound infection, phantom limb pain, skin necrosis (poor stump perfusion). Late: stump neuroma, osteomyelitis of stump, stump ulceration ^[6]

The Hong Kong Data

The lecture specifically highlights that in a HK series of 24 patients with necrotizing fasciitis, radical debridements (amputations and disarticulations) were performed in 46% and mortality ranges from 20 to 75% ^[1]. While this refers to necrotizing fasciitis broadly, PFT can be the initiating event that leads to NF of the hand. This is why we consider PFT a genuine emergency — delayed or missed diagnosis can set off a cascade ending in amputation or death.

5. Complications of Treatment

Complication	Mechanism	Prevention
Iatrogenic nerve injury	Digital nerves run adjacent to the sheath; can be damaged during incision or debridement	Careful dissection under direct vision; use of zig-zag incision (which avoids crossing directly over the neurovascular bundles)
Iatrogenic artery injury	Digital arteries similarly at risk	Identify and protect vessels during dissection
Pulley damage	Overzealous opening of the sheath may damage A2 or A4 pulleys → bowstringing (tendons pull away from bone during flexion → loss of mechanical advantage → weakness and poor flexion)	Preserve A2 and A4 pulleys during debridement; only open A3, A5, and cruciate pulleys if needed for access
Wound infection / delayed healing	Open wounds (left for secondary intention) are vulnerable to secondary infection and slow healing, especially in diabetic/immunocompromised patients	Aseptic dressing technique, optimise glycaemic control, adequate nutrition
Flexion contracture from scar	If a straight incision crosses a flexion crease → scar contracts → pulls joint into flexion	Zig-zag incision ^[1] prevents perpendicular scar across flexion creases

Complication	Mechanism
Allergic reaction / anaphylaxis	Hypersensitivity (especially to β-lactams — penicillins, cephalosporins). Always check allergy history
Nephrotoxicity	Vancomycin (dose-dependent tubular damage); aminoglycosides. Monitor trough levels and renal function
Ototoxicity	Vancomycin, aminoglycosides — damage to cochlear hair cells
Clostridioides difficile colitis	Prolonged broad-spectrum antibiotics disrupt gut flora → C. difficile overgrowth → pseudomembranous colitis. Risk highest with fluoroquinolones, clindamycin, broad-spectrum cephalosporins
Hepatotoxicity	Rifampicin (used for M. marinum) — monitor LFTs regularly
Optic neuritis	Ethambutol (used for M. marinum) — monitor visual acuity. Ethambutol = "Eye-thambutol" — the name helps you remember the side effect

These are often under-appreciated but profoundly affect patient quality of life:

Complication	Mechanism / Impact
Chronic pain / CRPS	Complex Regional Pain Syndrome (CRPS type I) can develop after any hand infection/surgery. Characterised by disproportionate pain, swelling, autonomic changes (colour/temperature asymmetry), and allodynia. Mechanism involves aberrant sympathetic nervous system activity and central sensitisation ^[6]
Loss of occupation	Many patients with PFT are manual workers (the demographic most exposed to hand injuries). A stiff, weak finger can make return to their occupation impossible
Psychological impact	Chronic pain, disability, disfigurement (amputation), prolonged hospitalisation → depression, anxiety, adjustment disorder
Financial burden	Prolonged hospital stay, multiple surgeries, rehabilitation, inability to work

Timing	Complication	Mechanism
Immediate (hours)	Tendon ischaemia	Rising intra-sheath pressure → vincular compression
Early (days)	Tendon necrosis; horseshoe abscess; deep space infection; septic arthritis; osteomyelitis; sepsis	Unrelieved pressure → necrosis; spread along anatomical pathways; bacteraemia
Intermediate (weeks)	Tendon adhesions; flexion contracture; necrotizing fasciitis; need for amputation	Fibrin deposition → organisation; fascial spread; non-viable tissue
Late (months–years)	Chronic stiffness; chronic pain / CRPS; occupational disability; psychological sequelae; stump complications (if amputated)	Adhesion maturation; central sensitisation; loss of function

High Yield Summary

Complications of PFT — Key Takeaways:

Tendon necrosis is the most feared complication — caused by vincular compression from rising intra-sheath pressure. Irreversible within 24–48 hours. This is why PFT is a surgical emergency.
Tendon adhesions and stiffness are the most common long-term complications — even with successful treatment. Early rehabilitation is essential.
Horseshoe abscess occurs when thumb or little finger PFT spreads via the radial/ulnar bursae and space of Parona to involve the opposite digit + forearm.
Contiguous spread can cause septic arthritis, osteomyelitis, and deep space infection of the hand.
Systemic complications: sepsis and necrotizing fasciitis — potentially fatal.
Amputation was performed in 46% of HK patients with hand NF; mortality 20–75% ^[1].
Risk factors for amputation: DM, renal failure, peripheral vascular disease ^[1].
Treatment complications: iatrogenic nerve/vessel injury, pulley damage → bowstringing, scar contracture, antibiotic toxicity.
Functional/psychosocial: CRPS, chronic pain, occupational disability, depression.

Active Recall - Complications of Infective Tenosynovitis

References

^[1] Lecture slides: GC 237. Musculoskeletal infection [Updated in 2025] (1).pdf (pages 2, 3, 24, 28, 29, 32, 44, 54) ^[2] Senior notes: maxim.md (section 506: trigger finger — Green's classification, pulley system) ^[4] Senior notes: maxim.md (sections 566–567: osteomyelitis, septic arthritis, necrotizing fasciitis — sequestrum/involucrum, LRINEC score) ^[6] Senior notes: maxim.md (section 454: complications of trauma — compartment syndrome, adhesions, CRPS, Volkmann's contracture); felixlai.md (section 1381: amputation — 3D indications, complications)

High Yield Summary

Infective (Pyogenic Flexor) Tenosynovitis — Key Points:

Definition: Closed space infection of the flexor tendon sheath of the hand — a surgical emergency
Epidemiology: 2.5–9.4% of all hand infections; most common in working-age adults after penetrating trauma
Most common organisms: Staphylococcus aureus and Streptococcus spp.; cover Gram-negatives and anaerobes in immunocompromised
Anatomy: The flexor tendon sheath is a sealed synovial tube; thumb and little finger sheaths communicate via the radial/ulnar bursae and space of Parona (horseshoe communication)
Pathophysiology: Infection in a non-distensible closed space → rising pressure → compression of vincula → tendon ischaemia → necrosis. Time is tendon.
Kanavel Signs (4):
- Fusiform (sausage) swelling of the entire finger
- Flexed posture at rest
- Tenderness along the entire flexor sheath (most sensitive)
- Pain on passive extension (most specific)
Risk factors for amputation: DM, renal failure, peripheral vascular disease
Management threshold: 1–2 Kanavel signs → trial of antibiotics; 3–4 Kanavel signs → surgical drainage + antibiotics
Hong Kong relevance: Marine injuries (M. marinum, Vibrio) from seafood handling; high DM prevalence

High Yield Summary

Differential Diagnosis of Infective Tenosynovitis — Key Takeaways:

The 4 Kanavel signs are the primary discriminators — no other condition produces all four simultaneously
Pain on passive extension (most specific) and tenderness along the entire flexor sheath (most sensitive) are the best signs to distinguish PFT from other finger infections
Three "cannot miss" diagnoses in a painful swollen hand: PFT, septic arthritis, necrotizing fasciitis — all require emergency surgical intervention ^[1]
Commonest diagnostic dilemma is PFT vs cellulitis — look for sheath-specific signs (fusiform swelling, flexed posture, pain on passive extension)
Sausage digit has a broad differential (PFT, dactylitis, gout) — acute onset + wound + Kanavel signs = PFT
PFT can coexist with or evolve from/into adjacent infections (felon → PFT → septic arthritis → osteomyelitis → deep space infection)
Necrotizing fasciitis: pain out of proportion, haemorrhagic bullae, systemic toxicity, dishwater pus, LRINEC > 8 ^[1] ^[4]

High Yield Summary

Diagnosis of PFT — Key Takeaways:

PFT is a CLINICAL diagnosis based on Kanavel's 4 cardinal signs ^[1] — no investigation can replace bedside assessment
Most sensitive sign: tenderness along the entire flexor sheath; Most specific sign: pain on passive extension
Threshold for surgery: 3–4 Kanavel signs → surgical emergency; 1–2 signs → trial of antibiotics with reassessment at 24 hours ^[1]
Investigations are supportive, not gate-keeping — prompt clinical diagnosis ^[1] takes priority
First-line imaging: X-ray (exclude fracture, foreign body, gas); USS (detect sheath fluid); MRI is not routine but best for complications ^[1]
Bloods: CBP, ESR, CRP ^[1] + blood cultures before antibiotics + renal function + glucose/HbA1c
Gold standard microbiology: intra-operative sheath fluid and tissue biopsy sent for Gram stain, C/ST (aerobic, anaerobic, AFB, fungal)
Alert the lab if you suspect M. marinum (30–32°C incubation) or N. gonorrhoeae (chocolate agar / NAAT)
Normal bloods do NOT exclude PFT — treat the patient, not the blood test

High Yield Summary

Management of PFT — Key Takeaways:

Prompt clinical diagnosis is the first and most important step ^[1]
Empirical antibiotics: cover Staph + Strep (IV cloxacillin); add Gram-negative and anaerobic cover in immunocompromised ^[1]
Non-operative treatment: early presentation within 48 hours, 1–2 Kanavel signs, mild symptoms → IV antibiotics + elevation + splinting + frequent examination → no improvement after 24–48 hours → surgery ^[1]
Operative treatment:
- Closed catheter irrigation: for moderate/established infection without necrosis ^[1]
- Open irrigation and debridement (zig-zag incision): for advanced infection, necrosis, chronic infection ^[1]
Post-operative: continued IV antibiotics tailored to cultures, wound care, elevation, splinting, early rehabilitation
Risk factors for amputation: DM, renal failure, peripheral vascular disease ^[1]
Always preserve A2 and A4 pulleys during open surgery to prevent bowstringing
Zig-zag incision prevents flexion contracture by avoiding perpendicular scars across flexion creases

High Yield Summary

Complications of PFT — Key Takeaways:

Tendon necrosis is the most feared complication — caused by vincular compression from rising intra-sheath pressure. Irreversible within 24–48 hours. This is why PFT is a surgical emergency.
Tendon adhesions and stiffness are the most common long-term complications — even with successful treatment. Early rehabilitation is essential.
Horseshoe abscess occurs when thumb or little finger PFT spreads via the radial/ulnar bursae and space of Parona to involve the opposite digit + forearm.
Contiguous spread can cause septic arthritis, osteomyelitis, and deep space infection of the hand.
Systemic complications: sepsis and necrotizing fasciitis — potentially fatal.
Amputation was performed in 46% of HK patients with hand NF; mortality 20–75% ^[1].
Risk factors for amputation: DM, renal failure, peripheral vascular disease ^[1].
Treatment complications: iatrogenic nerve/vessel injury, pulley damage → bowstringing, scar contracture, antibiotic toxicity.
Functional/psychosocial: CRPS, chronic pain, occupational disability, depression.

Infective Tenosynovitis

1. Definition

2. Epidemiology

3. Risk Factors

Patient Factors (Host Susceptibility)

Wound/Mechanism Factors

4. Anatomy and Function

4.1 The Flexor Tendon Sheath

4.2 The Pulley System

4.3 Extent of the Sheaths — The "Horseshoe" Communication

4.4 Blood Supply to the Flexor Tendons

4.5 Extensor Compartments (for context / DDx)

5. Etiology and Pathophysiology

5.1 Causative Organisms

5.2 Mechanisms of Infection

5.3 Pathophysiology — Step by Step

6. Classification

6.1 By Clinical Severity / Kanavel Signs

6.2 By Organism

6.3 By Mechanism

7. Clinical Features

7.1 Symptoms

7.2 Signs — The Four Kanavel Signs

7.3 Additional Clinical Signs

7.4 Special Scenarios

Horseshoe Abscess

Chronic/Granulomatous Tenosynovitis (M. marinum)

Gonococcal Tenosynovitis

8. Relevant Anatomy of the Hand for Context (from Lecture Slides)

9. Summary of Pathophysiology Cascade

Active Recall - Infective Tenosynovitis

References

Guiding Principle: What Makes PFT Unique?

Differential Diagnosis Table

Differential Diagnosis Decision Framework

Key Differentiating Features — The "Discriminators"

Approach to Narrowing the Differential

Special DDx Scenarios Worth Knowing

PFT vs Cellulitis

PFT vs Gout Flare (Podagra of the Hand)

PFT vs Disseminated Gonococcal Infection (DGI)

Active Recall - DDx of Infective Tenosynovitis

1. Diagnostic Criteria

1.1 Kanavel's Cardinal Signs — The Diagnostic Criteria

1.2 Why Is This a Clinical Diagnosis?

2. Diagnostic Algorithm

3. Investigation Modalities

3.1 Bedside Investigations

3.2 Blood Investigations

3.3 Imaging Investigations

3.4 Microbiological Investigations

Pre-operative Samples

Intra-operative Samples (taken during surgical irrigation/debridement)

3.5 Investigations for Differentials (When Diagnosis Is Uncertain)

4. Interpretation Framework: Putting It All Together

5. Summary Table: All Investigations at a Glance

Active Recall - Dx Criteria, Algorithm and Investigations for PFT

1. Overview of Management Principles

2. Management Algorithm

3. Treatment Modalities — Detailed Breakdown

3.1 General / Supportive Measures

3.2 Antibiotic Therapy

3.2.1 Empirical Antibiotics

3.2.2 Antibiotic Selection Logic Diagram

3.3 Non-Operative Treatment

Indications for Non-Operative Management

Non-Operative Protocol

Contraindications to Non-Operative Management

3.4 Operative Treatment

3.4.1 Closed Catheter Irrigation and Debridement

3.4.2 Open Irrigation and Debridement

3.4.3 Comparison of Surgical Approaches

3.5 Post-Operative Care

3.6 Special Situations

Amputation

Mycobacterium marinum Tenosynovitis

Horseshoe Abscess

4. Summary: Management by Clinical Scenario

Active Recall - Management of Infective Tenosynovitis

Overview