GC226 Lumbar Spine Pathology: Part E
Lumbar spine pathology Part E encompasses conditions such as lumbar spinal stenosis, spondylolisthesis, and cauda equina syndrome that cause narrowing of the spinal canal or neural foramina, leading to neurogenic claudication, radiculopathy, or acute neurological compromise.
Lumbar Spine Pathology – Part E: Pathologies (Differential Diagnosis, Common Causes, and Specific Conditions)
Lecturer: Professor Jason Pui Yin Cheung, Clinical Professor, HKU [1]
The Big Idea: Part E is the clinical meat of the lumbar spine series. After Parts A–D cover anatomy, examination, and investigations, Part E walks you through the differential diagnosis of back pain and then dives into the specific pathologies: myofascial sprain, disc degeneration, discogenic back pain, facet joint arthrosis, spondylolysis/spondylolisthesis, sacroiliac joint pain, and ankylosing spondylitis. This lecture defines what is causing the pain, why it hurts, and how to tell the conditions apart—which is exactly what examiners test.
Learning Objectives (from Part A, applying here): [2]
- Understand terminology of the lumbar spine
- Know examination skills for the lumbar spine
- Use investigations to diagnose specific conditions
- Understand how non-operative and operative solutions are decided
- Know common and rarer diseases clinicians encounter
How this fits into exams: The Fourth Summative regularly tests red flags of back pain, cauda equina syndrome, ankylosing spondylitis characteristics, and the difference between mechanical vs. non-mechanical back pain. Past paper stems (2020 SAQ Q5, 2021 MCQ Q70, 2023 Minicase Case 3, 2025 MCQ Q61) draw directly from this material.
1. Differential Diagnosis of Back Pain
High Yield — Directly from Lecture Slide: Back pain differential is split into Mechanical (97%) and Non-mechanical (3%). This proportion itself is commonly tested. [1]
| Category | Examples | Key Distinguishing Features |
|---|---|---|
| Back sprain | Myofascial strain | > 70% of all back pain; heals in ~4 weeks [1] |
| Lumbar disc degeneration | Age-related disc desiccation | Chronic; MRI shows loss of T2 signal |
| Lumbar disc herniation | Posterolateral > central > lateral | Radiculopathy; positive SLR |
| Spondylolisthesis | Anterior slip of vertebra | Palpable "step-off"; radicular symptoms |
| Fracture — Vertebral body | Osteoporotic compression fracture | Acute onset; wedge on XR |
| Fracture — Spondylolysis | Pars interarticularis defect | Young athlete; insidious LBP |
Why 97% is mechanical: The lumbar spine bears enormous load. The vast majority of back pain comes from normal wear-and-tear of the disc–facet–muscle complex. This means most patients do NOT need urgent imaging—they need reassurance, activity modification, and physiotherapy.
| Category | Examples |
|---|---|
| Neoplasia | Metastases (lung, breast, prostate, renal, thyroid), myeloma, lymphoma |
| Inflammatory arthritis | Ankylosing spondylitis / Spondyloarthropathy [1] |
| Infection | Discitis, vertebral osteomyelitis, epidural abscess, TB spondylitis |
| Non-spinal diseases | Pelvic inflammatory disease, Endometriosis, Nephrolithiasis, Pyelonephritis, Aortic aneurysm [1] |
Non-Spinal Causes Are Exam Favourites
Students often forget that aortic aneurysm can present as back pain (pulsatile abdominal mass + back pain = think AAA). Similarly, endometriosis (cyclical back pain in a young woman) and nephrolithiasis (colicky flank → back pain) are discriminators in MCQs. Always consider non-spinal causes when the pain pattern doesn't fit a mechanical story.
2. Common Causes of Back Pain — Detailed Pathology
High Yield: Myofascial sprain heals quickly in ~4 weeks. Treatment = avoid provocative activity. [1]
- Pathophysiology: Strain or micro-tears in paraspinal muscles and ligaments, typically from sudden loading or awkward posture.
- Why it heals in 4 weeks: Muscles have excellent blood supply → robust inflammatory/repair response. Unlike discs (avascular in centre), muscles regenerate.
- Management: Activity modification (avoid aggravating movements), short-course analgesia (paracetamol ± NSAIDs), gentle mobilisation. Avoid prolonged bed rest (deconditions muscles → worsens chronicity).
High Yield: Facet joint degeneration causes back pain and referred pain. Sources of pain include the outer annulus of the disc, the facet joint capsule, and chemical/mechanical irritation of the nerve root. [1]
Understanding the "pain generators":
- Outer annulus of disc: The outer 1/3 of the annulus fibrosus is innervated by the sinuvertebral nerve. When it tears, nociceptive fibres are directly stimulated → axial back pain.
- Facet joint capsule: Facet joints are synovial joints with a richly innervated capsule. Osteoarthritic changes → inflammation → capsular stretch → pain, especially on extension.
- Chemical and mechanical irritation of nerve root: Herniated disc material (nucleus pulposus) releases pro-inflammatory cytokines (TNF-α, IL-1, IL-6, PGE2). Even without direct compression, chemical inflammation of the nerve root causes radicular pain.
3. Discogenic Back Pain
High Yield: Discogenic back pain is worse in forward flexion postures — sitting, bending forward to tie shoes. Caused by: biomechanical problems (Modic changes), cytokine release (inflammatory), ingrowth of nerve and vasculature to the disc after annular tear. Features: high intensity zone (HIZ) and posterior annulus fissure on MRI. [1]
When you flex the lumbar spine (sit, bend forward), intradiscal pressure increases dramatically. The nucleus pulposus is pushed posteriorly against the weakened posterior annulus. This is the opposite of facet pain (which worsens in extension). This distinction is a classic exam discriminator:
| Feature | Discogenic Pain | Facet Joint Pain |
|---|---|---|
| Worse with | Forward flexion, sitting | Extension, lateral bending |
| Better with | Extension, lying flat | Flexion |
| Pain location | Midline / axial | Paravertebral, may refer to buttock/thigh |
| Key investigation | MRI (HIZ, Modic changes) | MRI, facet joint injection (diagnostic + therapeutic) |
-
Biomechanical (Modic changes):
- Modic Type 1: Bone marrow oedema adjacent to endplates → active inflammatory phase → pain
- Modic Type 2: Fatty replacement → chronic phase → less pain
- Modic Type 3: Sclerosis → "burned out"
- Why it matters: Modic 1 changes on MRI correlate with active discogenic pain; seeing them tells you the disc is a likely pain generator.
-
Cytokine release (inflammatory):
- Degenerated disc releases TNF-α, IL-1β, IL-6, PGE2
- These chemicals sensitise nociceptors in the annulus and adjacent structures
- This explains why patients can have severe pain even without massive disc herniation
-
Nerve/vascular ingrowth into disc after annular tear:
- Normal adult disc is avascular in its inner portion and has no nerve supply beyond the outer 1/3 of annulus
- After an annular tear, granulation tissue with neoinnervation (substance P–positive nociceptive fibres) and neovascularisation grows into the disc
- This converts the previously aneural inner disc into a pain-generating structure — a fundamental reason why disc degeneration becomes painful
- What it is: A bright signal on T2-weighted MRI within the posterior annulus fibrosus
- What it represents: An annular tear with associated granulation tissue, inflammation, and neovascularisation
- Clinical significance: Strong indicator that the disc is a pain source (discogenic pain); seen in symptomatic patients; correlates with concordant pain on provocative discography
- A radial tear extending from the nucleus pulposus through to the posterior annulus
- Allows nucleus pulposus to track posteriorly → may herniate → chemical irritation of nerve root even before mechanical compression occurs
4. Facet Joint Arthrosis
High Yield: Facet joint arthrosis causes pain on extension and lateral extension towards the side of facet joint arthrosis. It indicates overload of facet joints as part of the disc degenerative cascade (disease origin at the disc). Management: back muscle strengthening and facet joint injections. [1]
This is a critical concept the lecturer emphasises:
- Disc degenerates first → loss of disc height → increased load on facet joints
- Facet joints are now overloaded → articular cartilage wear → osteophyte formation → facet hypertrophy
- Hypertrophied facets → lateral canal (foraminal) stenosis → compression of the exiting nerve root
- This is shown on the lecture slides as: Disc degeneration → Facet joint problem → Lateral canal stenosis [1]
Why it hurts on extension: When you extend the lumbar spine, the facet joints are compressed together (they "telescope" on each other). An already arthritic facet joint becomes exquisitely painful under this loading. Lateral bending towards the affected side similarly compresses the ipsilateral facet.
- Back muscle strengthening: Strong paraspinal and core muscles take load off the facet joints → reduces pain. This is conservative first-line management.
- Facet joint injections: Intra-articular corticosteroid + local anaesthetic under fluoroscopic guidance. Also serves as a diagnostic tool (if pain resolves, the facet is confirmed as the pain source). If there is a good but temporary response, radiofrequency ablation of the medial branch nerve can provide longer-lasting relief.
Exam Discriminator: Disc vs. Facet Pain
If a stem says "pain worse sitting / bending forward" → think disc. If a stem says "pain worse leaning backward / extension" → think facet. This distinction appears repeatedly in MCQs.
5. Spondylolysis and Spondylolisthesis
High Yield: Spondylolysis presents with LBP with insidious onset. Radicular symptoms occur only with spondylolisthesis. Physical findings: hamstring spasm (flexed hips and knees), shortened stride length, flattened lordosis. [1]
Definition: A defect (fracture) of the pars interarticularis — the bony bridge connecting the superior and inferior articular processes of a vertebra.
Why it happens:
- Most common at L5 (the junction between the mobile lumbar spine and fixed sacrum creates maximal shear stress)
- In young athletes: repetitive hyperextension and rotation (gymnasts, fast bowlers in cricket, football linemen) → stress fracture of the pars
- In older adults: may be due to degenerative changes weakening the pars
Clinical Features Explained:
- Insidious onset LBP: Because it's a stress fracture, not an acute traumatic fracture. Develops over weeks–months of repetitive loading.
- Hamstring spasm: The body's protective mechanism — tight hamstrings tilt the pelvis posteriorly, reducing lumbar lordosis, thereby reducing shear stress across the defective pars. This is why patients walk with flexed hips and knees.
- Shortened stride length: Hamstring tightness limits hip extension during gait → shorter steps
- Flattened lordosis: Secondary to hamstring tightness and posterior pelvic tilt (protective adaptation)
- Radicular symptoms only with spondylolisthesis: The pars defect alone doesn't compress nerves. Only when the vertebra slips forward (spondylolisthesis) does the foraminal narrowing cause nerve root compression.
High Yield: Spondylolisthesis represents radiological instability and end-stage degeneration. It causes spinal stenosis by kinking centrally or compression by the superior articular process impingement at the neuroforamen. [1]
Definition: Anterior translation (slip) of one vertebra on the one below.
Types (Wiltse Classification):
| Type | Mechanism | Typical Patient |
|---|---|---|
| I — Dysplastic | Congenital deficiency of superior sacral facet | Children |
| II — Isthmic | Pars interarticularis defect (spondylolysis) | Young athletes, most common type |
| III — Degenerative | Facet/disc degeneration → instability | Older adults, F > M, L4/5 most common |
| IV — Traumatic | Acute fracture other than pars | Trauma patients |
| V — Pathological | Bone disease (tumour, infection) | Variable |
Grading (Meyerding):
| Grade | Percentage of slip |
|---|---|
| I | 0–25% |
| II | 25–50% |
| III | 50–75% |
| IV | 75–100% |
| V (Spondyloptosis) | > 100% |
How it causes nerve compression:
- Central kinking: The vertebral body slips forward → the spinal canal narrows at the level of slip → cauda equina compression (central stenosis)
- Foraminal stenosis by superior articular process (SAP) impingement: As the vertebra slips, the SAP of the vertebra below encroaches on the neuroforamen → exiting nerve root compression
High Yield: Investigations: Radiographs, Single-photon emission CT (SPECT) — shows increased radionuclide uptake as stress reaction, CT, MRI. [1]
| Investigation | What It Shows | When to Use |
|---|---|---|
| Plain radiographs | Pars defect ("Scotty dog" sign on oblique view: the "collar" = pars defect); slip on lateral view | First-line; assess degree of slip |
| SPECT | Increased uptake = active stress reaction/healing potential | Distinguish active vs. chronic/healed pars defect (crucial for deciding if bracing will help) |
| CT | Detailed bony anatomy of pars defect | Confirm equivocal XR findings; pre-operative planning |
| MRI | Soft tissue; disc status; nerve root compression; bone marrow oedema | Evaluate for neurological compromise or disc pathology |
Why SPECT is special: A "hot" pars defect on SPECT means there is active bone remodelling → the fracture has healing potential → bracing may allow it to unite. A "cold" defect is chronic and established → unlikely to heal with conservative management.
- Without spondylolisthesis: Activity modification, bracing (if SPECT-positive), physiotherapy (core strengthening), NSAIDs
- Surgical indications: Progressive neurological deficit, intractable pain despite conservative treatment, high-grade slip (≥Grade III)
Why Fusion Is Needed With Spondylolisthesis
If you decompress (remove bone from the posterior spine) in a patient who already has an unstable slip, you remove the last remaining stabilisers → the slip worsens. Fusion (with pedicle screws and rods ± interbody cage) locks the vertebrae together, preventing further translation. This is a commonly tested surgical principle.
High Yield: Sacroiliac joint (SIJ) pain accounts for a significant proportion of LBP patients: Maigne — 18.5% (Spine 1996), Schwarzer — 30% (Spine 1995). [1]
Why SIJ pain is under-recognised:
- The SIJ is a large, weight-bearing joint that transmits forces between the spine and pelvis
- Pain referral patterns overlap with lumbar facet and disc pain (buttock, posterior thigh, groin)
- No single clinical test is highly sensitive or specific; a cluster of provocation tests (Gaenslen's, FABER/Patrick's, thigh thrust, sacral compression, distraction) improves diagnostic accuracy
- Gold standard: Diagnostic SIJ injection under fluoroscopic guidance (> 75% pain relief confirms the SIJ as the pain source)
Common causes of SIJ pain:
- Degenerative sacroiliitis
- Post-partum SIJ dysfunction
- Inflammatory (ankylosing spondylitis — see below)
- Trauma
7. Ankylosing Spondylitis (AS)
High Yield: Ankylosing spondylitis is a spondyloarthropathy — can be axial vs. peripheral. Characterised by asymmetrical peripheral arthritis. Affects women as well as men (M:F = 6:1 aged < 16; M:F = 2:1 aged 30). Shows familial aggregation. Associated with HLA-B27 — but NOT diagnostic. Rheumatoid factor negative. [1]
What is it? AS is a chronic inflammatory disease that primarily targets the axial skeleton (sacroiliac joints and spine) and entheses (where tendons/ligaments attach to bone). Over time, chronic inflammation leads to new bone formation → spinal fusion ("bamboo spine").
Why HLA-B27 is not diagnostic:
- ~90% of AS patients are HLA-B27 positive, BUT ~8% of the general population is also HLA-B27 positive
- Most HLA-B27 positive individuals never develop AS
- Therefore, HLA-B27 supports the diagnosis in the right clinical context but is neither sufficient nor necessary for diagnosis
Why rheumatoid factor negative matters:
- Distinguishes spondyloarthropathies from rheumatoid arthritis
- AS is a "seronegative" spondyloarthropathy (RF negative, anti-CCP negative)
- The pattern of joint involvement (axial, asymmetric, large joints, enthesitis) is fundamentally different from RA (symmetrical, small joints)
Why it affects women too:
- Historical teaching over-emphasised male predominance
- The lecturer explicitly states women are affected — the ratio narrows with age (2:1 by age 30)
- Women may present with more peripheral disease and less severe radiographic changes → diagnostic delay
High Yield: Inflammatory back pain criteria: Onset before age 40, insidious onset, persistent for at least 3 months, associated with morning stiffness, improvement with exercise. [1]
| Feature | Inflammatory Back Pain (IBP) | Mechanical Back Pain |
|---|---|---|
| Age of onset | < 40 years | Any age |
| Onset | Insidious | Often acute/identifiable trigger |
| Duration | ≥ 3 months | Variable |
| Morning stiffness | Prominent (> 30 minutes, often > 1 hour) | Brief (< 30 min) or absent |
| Effect of exercise | Improves | Often worsens |
| Effect of rest | Worsens (stiffness after sitting) | Improves |
| Night pain | Yes, especially 2nd half of night | Uncommon unless severe |
| Alternating buttock pain | Characteristic (SIJ inflammation) | No |
Why exercise improves IBP: Inflammatory cytokines cause stiffness by promoting fibrin deposition and oedema in joint capsules/entheses during rest. Movement increases blood flow, clears inflammatory mediators, and breaks up adhesions. This is fundamentally different from mechanical pain where loading aggravates the injured structure.
High Yield: Early diagnosis of AS is essential. Use clinical, radiological, blood tests, and MRI. [1]
Why early diagnosis matters:
- Early treatment with biologics (TNF-α inhibitors like adalimumab, etanercept; or IL-17 inhibitors like secukinumab) can slow progression and prevent irreversible structural damage
- Average diagnostic delay is still 7–10 years from symptom onset
- MRI can detect sacroiliitis before plain radiographs show changes (pre-radiographic axial SpA)
Investigations:
| Investigation | Finding | Significance |
|---|---|---|
| Plain XR sacroiliac joints | Sclerosis, erosions, widening → eventual ankylosis | Late finding; may be normal early in disease |
| MRI sacroiliac joints | Bone marrow oedema on STIR/T2-FS = active sacroiliitis | Early finding; used in ASAS criteria for non-radiographic axial SpA |
| HLA-B27 | Positive in ~90% AS patients | Supports diagnosis but NOT diagnostic |
| ESR / CRP | Elevated (but can be normal in up to 40%) | Helps monitor disease activity |
| Rheumatoid factor | Negative | Distinguishes from RA |
- Clinical: Low back pain ≥ 3 months improved by exercise, limitation of lumbar spine motion (sagittal & frontal), limited chest expansion
- Radiographic: Bilateral sacroiliitis ≥ Grade 2, or unilateral ≥ Grade 3
- Definite AS: Radiographic criterion + ≥ 1 clinical criterion
- Used for early/non-radiographic disease
- Sacroiliitis on imaging (MRI or XR) + ≥ 1 SpA feature, OR HLA-B27 positive + ≥ 2 SpA features
- SpA features: IBP, arthritis, enthesitis, dactylitis, psoriasis, IBD, uveitis, good response to NSAIDs, family history, HLA-B27, elevated CRP
| Category | Examples |
|---|---|
| NSAIDs | First-line; continuous use if needed (e.g. diclofenac, naproxen, celecoxib) |
| Biologics — TNF-α inhibitors | Adalimumab, etanercept, infliximab (for refractory to ≥ 2 NSAIDs) |
| Biologics — IL-17 inhibitors | Secukinumab, ixekizumab |
| DMARDs | Sulfasalazine (mainly for peripheral arthritis; limited axial efficacy) |
| Physiotherapy | Essential; maintains posture, spinal mobility, chest expansion |
Exam Pearl: AS Drug Groups
The 2020 SAQ explicitly asked: "Name two specific groups of drugs that could be used for AS." The answer is NSAIDs and biologic DMARDs (TNF-α inhibitors). Conventional DMARDs like methotrexate have NO proven efficacy for axial disease in AS — a common trap. [6]
8. Clinical Approach Summary
| Question | What You're Looking For |
|---|---|
| Age of onset | < 40 → consider AS; > 50 → consider malignancy, osteoporotic fracture |
| Onset | Acute (sprain, fracture) vs. insidious (degeneration, AS, tumour) |
| Duration | > 3 months + morning stiffness → inflammatory |
| Aggravating factors | Flexion → disc; Extension → facet; Walking → stenosis/claudication |
| Relieving factors | Rest → mechanical; Exercise → inflammatory |
| Night pain | Red flag → tumour, infection, inflammatory |
| Neurological symptoms | Leg pain, numbness, weakness, bladder/bowel disturbance |
| Red flags | Weight loss, fever, history of cancer, IV drug use, immunosuppression, saddle anaesthesia, bilateral leg weakness, urinary retention |
- Look: Sciatic list, loss of lordosis, scoliosis, step-off (spondylolisthesis)
- Feel: Paraspinal tenderness/spasm, spinous process tenderness (infection, fracture), SIJ tenderness
- Move: Flexion (Schober's < 5 cm = limited → AS), extension, lateral flexion
- Special tests: SLR (L5/S1 root), femoral stretch test (L3/4 root), crossed SLR (highly specific)
- Neurology: Myotomal power, dermatome sensation, reflexes (knee L3/4, ankle S1)
From 2023 Minicase Section 1: "Name four red flag signs for back pain" [9]
| Red Flag | Concern |
|---|---|
| Fever / systemic illness | Infection (discitis, epidural abscess) |
| Unexplained weight loss | Malignancy |
| History of malignancy | Spinal metastasis |
| Age > 50 or < 20 with new back pain | Tumour, infection, structural pathology |
| Night pain (unremitting) | Tumour, infection |
| Progressive neurological deficit | Cord/cauda equina compression |
| Saddle anaesthesia / bladder/bowel dysfunction | Cauda equina syndrome — surgical emergency |
| IV drug use / immunosuppression | Spinal infection |
| Trauma | Fracture |
| Corticosteroid use | Osteoporotic fracture |
High Yield: Spinal stenosis occurs by kinking centrally or compression by the superior articular process impingement at the neuroforamen. [1]
Pathophysiology:
- Disc degeneration → loss of height → bulging annulus → facet hypertrophy → ligamentum flavum buckling and thickening → canal narrowing
- Central stenosis → compression of cauda equina → neurogenic claudication
- Lateral/foraminal stenosis → compression of exiting nerve root → radiculopathy
Neurogenic vs. Vascular Claudication:
| Feature | Neurogenic Claudication | Vascular Claudication |
|---|---|---|
| Aggravated by | Walking AND standing | Walking only |
| Relieved by | Sitting / flexing spine ("shopping cart sign") | Standing still |
| Cycling | Usually pain-free (flexed posture) | May still cause pain |
| Pulses | Normal | Reduced/absent |
| Skin | Normal | Trophic changes, hair loss |
| Pain distribution | Bilateral/diffuse, "heavy legs" | Calves, follows arterial territory |
Why flexion helps: Lumbar flexion opens the spinal canal (increases antero-posterior diameter) → reduces neural compression. This is why patients lean on shopping carts or sit → pain relief ("park bench to park bench" pattern) [4].
10. Integration with Related Conditions
- Scenario: Middle-aged obese man, acute back pain + urinary incontinence + buttock numbness + bilateral LL weakness after heavy lifting → Cauda equina syndrome (Answer: B)
- Mechanism: Massive central disc herniation at L4/5 or L5/S1 compresses the cauda equina
- Management: Surgical emergency — MRI → urgent decompressive laminectomy/discectomy within 24–48 hours (ideally < 24h) [4]
- Scenario: 56-year-old with metastatic lung cancer, severe LBP, LL power 3/5, pathological collapse L1 with cord compression
- Answer: C — Start high-dose steroids and arrange urgent orthopaedic consultation for decompressive surgery
- Why: Dexamethasone reduces vasogenic oedema around the compressed cord → buys time. Surgical decompression + stabilisation improves outcomes if life expectancy > 3 months. PET-CT and bone scan are for staging, not acute management.
Past Paper Questions
Stem: "A 26-year-old man with a history of recurrent uveitis, alternating buttock pain, and bilateral plantar fasciitis has complained of lower back pain for 6 months. You suspect a diagnosis of ankylosing spondylitis. (a) Name four characteristics of back pain in this condition. (4 marks) (b) Lumbosacral spine radiograph of the man was normal. Name two investigations that you would perform to make the diagnosis. (2 × 2 marks) (c) Name two specific groups of drugs that could be used for the disease. (2 marks)"
Markscheme:
- (a) Onset before age 40; insidious onset; persistent ≥ 3 months; associated with morning stiffness; improvement with exercise — any 4
- (b) MRI sacroiliac joints (detects early sacroiliitis); HLA-B27; ESR/CRP — any 2
- (c) NSAIDs; Biologic DMARDs (TNF-α inhibitors e.g. adalimumab) — "two specific groups"
- Trap: Do not write "methotrexate" — it has no proven axial efficacy in AS
Stem: "A middle-aged obese man developed acute back pain, urinary incontinence, buttock numbness and bilateral lower limb weakness after lifting heavy objects at work. What is the MOST LIKELY diagnosis? A. Aortic dissection B. Cauda equina syndrome C. Psoas abscess D. Transverse myelitis"
Answer: B — Cauda equina syndrome
- Discriminator: The combination of urinary incontinence + saddle area numbness + bilateral LL weakness after acute loading = textbook CES from massive central disc herniation. Transverse myelitis would present with UMN signs (hyperreflexia, upgoing plantars) — CES gives LMN signs (areflexia, flaccid).
Stem: "Mr. Chan, 75 y/o, lower back pain for a few weeks, low-grade fever since last week. BP 152/77, HR 95, SpO2 98%, T 38°C. Urinalysis normal. Q1: Name four red flag signs for back pain (8 marks) Q2: Name three most likely differential diagnoses (6 marks) Q3: Name three investigations (6 marks)"
Markscheme:
- Q1: Fever, age > 50, neurological deficit, weight loss, history of cancer, immunosuppression, night pain, saddle anaesthesia, bladder/bowel dysfunction — any 4
- Q2: Spinal infection (pyogenic spondylodiscitis), spinal metastasis / malignancy, TB spondylitis (Pott's disease)
- Q3: Blood tests (CBC, CRP, ESR, blood culture), MRI lumbar spine, CT-guided biopsy (if infection or tumour suspected)
Stem: "A 56-year-old gentleman was receiving chemotherapy for his metastatic lung cancer. He was admitted through A&E for severe low back pain. His lower limb power was 3 out of 5. MRI noted a pathological collapse of the L1 vertebra with cord compression. What is the MOST APPROPRIATE initial management?"
Answer: C — Start high-dose steroids and arrange urgent orthopaedic consultation for decompressive surgery
- Discriminator: This is acute metastatic cord compression → dexamethasone (reduces oedema, buys time) + urgent surgical decompression. Staging (PET-CT/bone scan) and radiotherapy are appropriate later but not the initial step.
Stem: "A 70-year-old man has chronic neck pain. He sustains a fall on level ground causing hyperextension of his neck. Plain X-rays show multiple osteophytes and narrowing of the spinal canal. MRI showed hyperintense signals on T2 sequence within the cervical spinal cord. What is MOST LIKELY present on clinical examination? A. Clumsy hand movement B. Foot drop C. Loss of proprioception in lower limbs D. Urinary retention"
Answer: A — Clumsy hand movement
- Rationale: This is acute-on-chronic cervical myelopathy (central cord syndrome pattern after hyperextension in a spondylotic spine). Myelopathic hand signs (clumsy hand, finger escape sign, grip-release test) are early and characteristic. Foot drop = L5 radiculopathy (peripheral, not cord). Loss of proprioception and urinary retention are later features.
Exam Intelligence
| Trap | Correct Approach |
|---|---|
| Confusing disc pain (flexion) with facet pain (extension) | Remember: sitting/bending = disc; standing/extending = facet |
| Thinking HLA-B27 is diagnostic of AS | It SUPPORTS but is NOT diagnostic (~8% of normal population is positive) |
| Writing "methotrexate" for AS treatment | Methotrexate has NO proven axial efficacy in AS; correct = NSAIDs + biologics |
| Confusing neurogenic vs. vascular claudication | Neurogenic: relieved by sitting/flexion; Vascular: relieved by standing still |
| Calling CES an "UMN" lesion | CES = cauda equina = nerve roots = LMN (flaccid, areflexic). UMN signs = cord lesion (above conus) |
| Missing non-spinal causes of back pain | Always consider AAA, renal pathology, endometriosis, PID |
| Forgetting spondylolysis can exist without spondylolisthesis | Spondylolysis = pars defect. Spondylolisthesis = vertebral slip. Not the same. |
| Decompression-only surgery in spondylolisthesis | If there's instability (slip), you MUST add fusion to decompression |
- MCQ: "Which feature distinguishes inflammatory from mechanical back pain?" → Morning stiffness improving with exercise
- SAQ: "Name the features of inflammatory back pain" → 5 criteria from slide
- Minicase: Back pain in elderly with fever → differential and red flags
- OSCE: Lumbar spine examination including SLR, Schober's test, and discussion of findings
High Yield Summary
1. Back pain differential: Mechanical (97%) vs. Non-mechanical (3%). Back sprain is the commonest cause ( > 70%).
2. Discogenic pain: Worse in flexion/sitting. Caused by biomechanical (Modic changes), inflammatory (cytokines), and neoinnervation mechanisms. MRI features: HIZ, posterior annular fissure.
3. Facet joint arthrosis: Worse in extension. Part of disc degenerative cascade (disc → facet → lateral stenosis). Treat with muscle strengthening and facet injections.
4. Spondylolysis: Pars interarticularis defect. Insidious LBP in young athletes. Hamstring spasm, shortened stride, flattened lordosis. SPECT shows active stress reaction. Radicular symptoms only if spondylolisthesis develops.
5. Spondylolisthesis: Anterior vertebral slip. Causes stenosis by central kinking or foraminal impingement. Surgery requires decompression + fusion (not decompression alone).
6. SIJ pain: 18.5–30% of LBP patients. Diagnosed by provocation tests + diagnostic injection.
7. Ankylosing spondylitis: Inflammatory back pain onset < 40y, insidious, ≥ 3 months, morning stiffness, improves with exercise. HLA-B27 associated (not diagnostic). RF negative. MRI SIJ for early diagnosis. Treatment: NSAIDs + biologics (TNF-α or IL-17 inhibitors).
8. Red flags: Fever, weight loss, cancer history, neurological deficit, saddle anaesthesia, bladder/bowel dysfunction → urgent investigation.
9. CES is a surgical emergency: Massive central disc herniation → bilateral LL weakness + urinary retention + saddle anaesthesia → urgent MRI + decompression.
10. Metastatic cord compression: High-dose steroids first + urgent surgical decompression.
Active Recall - Lecture Notes
[1] Lecture slides: GC 226. Lumbar Spine Pathology_Part E.pdf (all slides p1–p18) [2] Lecture slides: GC 226. Lumbar Spine Pathology_Part A.pdf (p2, Learning Objectives) [3] Senior notes: Maksim Surgery Notes.pdf (p225, Management of spinal stenosis and spondylolisthesis) [4] Senior notes: Ryan Ho Neurology.pdf (p174, Lumbar canal stenosis and neurogenic claudication) [5] Senior notes: Ryan Ho Fundamentals.pdf (p145–148, Spine examination) [6] Past papers: 2020 Fourth Summative SAQ.pdf (Q5, Ankylosing spondylitis) [7] Past papers: 2021 Fourth Summative Assessment MCQ.pdf (Q70, Cauda equina syndrome) [8] Past papers: 2025 Fourth Summative MCQ.pdf (Q61, Metastatic cord compression) [9] Past papers: 2023 Fourth Summative Minicase.pdf (Case Three, Sections 1–5, Back pain red flags) [10] Past papers: 2025 Fourth Summative MCQ.pdf (Q88, Cervical myelopathy)
GC226 Lumbar Spine Pathology: Part D
Lumbar spine pathology Part D encompasses advanced degenerative, infectious, neoplastic, and inflammatory conditions of the lumbar spine, including spinal stenosis, spondylolisthesis, discitis, and metastatic disease, with emphasis on diagnostic evaluation and management strategies.
GC226 Lumbar Spine Pathology: Part F
Lumbar spine pathology Part F encompasses advanced topics such as spinal infections (discitis, osteomyelitis), tumors (primary and metastatic), and inflammatory conditions (ankylosing spondylitis) affecting the lumbar vertebral column.