UKMLA Musculoskeletal & Rheumatology: High-Yield Guide

Musculoskeletal and rheumatology questions are underestimated on UKMLA. Many students dismiss them as "read the joint, give NSAIDs" — then fail to pick out the cauda equina from back pain, or miss septic arthritis hiding in a slightly swollen knee. The GMC content map lists at least sixteen MSK and rheumatological conditions, and the AKT favours the ones that kill or cripple: septic arthritis, cauda equina, compartment syndrome, giant cell arteritis. Miss any of those in a SBA and you choose wrong.

This guide is the pillar for MSK on UKMLA. We walk through every emergency first (because they're SBA gold), then the chronic rheumatology canon (RA, OA, SLE, vasculitides, seronegative spondyloarthropathies), then fractures and back-pain triage. For each, we give the clinical pattern that matches the UKMLA stem, the gold-standard investigation, and the NICE-aligned management. Use it alongside our UKMLA emergency presentations masterclass for cauda equina and compartment syndrome overlap, and our neurology guide for the sciatica-vs-cauda decision tree.

1. Why MSK Emergencies Dominate MSK SBAs

Open any UKMLA-aligned question bank and count how many MSK SBAs are actually about osteoarthritis management. You'll find almost none. The examiners care about the ones that hurt patients if missed: septic arthritis (40% mortality in the elderly if untreated), cauda equina (permanent incontinence within hours), compartment syndrome (limb loss within six hours), GCA (blindness within days).

This means a disproportionate fraction of your MSK revision should go into recognition algorithms — the two-sentence stem that should make you reach for aspiration, MRI, fasciotomy, or 60 mg prednisolone. The chronic conditions (RA, OA, gout) matter too, but those are usually single-step questions: "which drug next?" The emergencies are multi-step: recognise → investigate → treat in the right order.

Approach every MSK SBA by asking three questions: (1) Is this a surgical emergency (septic joint, cauda equina, compartment syndrome, fracture)? (2) Is there systemic inflammation (temporal headache, uveitis, mucocutaneous signs)? (3) Is it mechanical (age, exertion pattern, improves with rest)? The answers cluster the differential within seconds.

2. Septic Arthritis — Red Flags, Aspiration, Empirical Antibiotics

Septic arthritis is the "hot joint" that kills. In the UK the classic organism is Staphylococcus aureus, with gonorrhoea in young sexually active patients. Risk factors include rheumatoid arthritis (damaged joints are easy targets — RA patients have 10x risk), prosthetic joints, diabetes, immunosuppression, IV drug use, and recent joint injection.

The stem: acute monoarthritis (usually knee), systemic features (fever, tachycardia), unable to weight-bear. Examination: warm, swollen, exquisitely tender, near-zero range of motion. Kocher criteria (fever >38.5°C, non-weight-bearing, WCC >12, ESR >40) support the diagnosis but don't rule out — if you suspect it clinically, aspirate.

Investigation: urgent joint aspiration before antibiotics (gram stain + culture + WCC + crystals). Blood cultures, FBC, CRP, ESR, urate. X-ray usually normal early. Synovial WCC >50,000 with neutrophil predominance supports infection; crystals can coexist (septic + gout in the same joint is a classic trap).

Management (BSR 2006): empirical IV flucloxacillin (clindamycin if penicillin-allergic, vancomycin if MRSA risk), joint washout by orthopaedics, analgesia, splint in function position. Duration typically 2 weeks IV then 4 weeks oral (6 weeks total). For gonococcal, ceftriaxone + azithromycin + partner notification.

SBA trap: a patient with known RA on methotrexate develops a hot, swollen, painful knee over 24 hours. "What is the next investigation?" Answer: urgent joint aspiration. NOT "start oral flucloxacillin" — you need a sample first, and you need IV antibiotics after.

3. Osteomyelitis — Acute vs Chronic, Imaging

Osteomyelitis is bone infection — either haematogenous (usually children, metaphyseal long bone) or contiguous spread (diabetic foot, open fracture, post-surgical). Acute presents with bone pain, fever, focal tenderness; chronic presents with sinus tracts, draining pus, non-healing ulcers.

Imaging: plain X-rays lag by 10–14 days (look for periosteal reaction, lytic lesions, sequestrum). MRI is the gold standard — bone marrow oedema in 24–48 hours. CT useful for sequestrum and surgical planning.

Management: prolonged IV antibiotics (typically 6 weeks) tailored to culture. Flucloxacillin empirically in adults, adjusted once cultures return. Surgical debridement for chronic disease, sinus tracts, or sequestra. Vertebral osteomyelitis (discitis) is increasing in IVDU and the elderly — suspect in back pain + fever + elevated CRP, confirm on MRI.

UKMLA trap: a diabetic with a non-healing foot ulcer and a positive probe-to-bone test — diagnosis is osteomyelitis until proven otherwise. Order MRI, not another course of oral antibiotics.

4. Cauda Equina Syndrome — Red Flags and Timing

Cauda equina is compression of the lumbosacral nerve roots below the conus medullaris, typically by a massive central disc herniation (L4/L5 or L5/S1). It is a surgical emergency within 24 hours — decompression timing correlates with recovery of bladder function.

The red flags (NICE NG59):

• Bilateral sciatica (especially new)
• Saddle anaesthesia (perineal numbness — ask specifically)
• Urinary retention or overflow incontinence
• Faecal incontinence / reduced anal tone on PR
• Lower-limb weakness (variable)
• Sexual dysfunction (difficulty ejaculating, decreased sensation)

Investigation: urgent MRI lumbosacral spine — do NOT wait for the outpatient slot. Bladder scan if retention suspected.

Management: immediate referral to spinal surgery (or neurosurgery). Definitive treatment is surgical decompression, ideally within 24 hours of symptom onset and certainly before complete CES (retention with overflow).

SBA trap: the stem will mention "new urinary incontinence" or "numbness when I wipe" buried in otherwise classic sciatica. The right answer is always MRI lumbosacral spine — not physio, not more analgesia, not an outpatient referral.

See UKMLA emergency presentations for the full CES decision tree.

5. Compartment Syndrome — The 6 Ps and Pressures

Compartment syndrome is raised pressure within a closed fascial compartment compromising perfusion. Usually post-fracture (tibia, forearm), post-reperfusion, post-prolonged immobilisation, or post-burns. Untreated it causes muscle necrosis and limb loss within 4–6 hours.

The 6 Ps (learn all six, the first is most important):

1. Pain out of proportion to injury — the cardinal sign, worsened by passive stretch of the affected muscle
2. Paraesthesia — early sensory nerve ischaemia
3. Pallor — late
4. Paralysis — late
5. Pulselessness — very late (pulses are often preserved until irreversible damage)
6. Poikilothermia — late

The reverse of ischaemic limbs: pulses are the last thing to go in compartment syndrome. Do not wait for pulselessness.

Diagnosis: clinical. In unconscious or obtunded patients, compartment pressures >30 mmHg (or delta pressure <30 mmHg, i.e. DBP minus compartment pressure) are diagnostic.

Management: remove casts/dressings, limb at heart level (not elevated — that reduces perfusion), urgent orthopaedics review, emergency fasciotomy. Analgesia with caution — opioids blunt the cardinal sign.

6. Rheumatoid Arthritis — Classification, DMARDs, Biologics

RA is symmetric inflammatory polyarthritis of small joints (MCPs, PIPs, wrists, MTPs, sparing the DIPs) with morning stiffness >1 hour. Extra-articular features include rheumatoid nodules, scleritis, pulmonary fibrosis, amyloidosis, and secondary Sjögren's.

Serology: rheumatoid factor (70–80% sensitivity, non-specific), anti-CCP (70% sensitivity, 95% specificity, prognostic). ESR and CRP track disease activity. X-rays show periarticular erosions, joint space narrowing, and subluxation (late).

2010 ACR/EULAR classification criteria (score ≥6/10): joints involved, serology, inflammatory markers, symptom duration ≥6 weeks.

Management (NICE NG100, 2020):

• First line: methotrexate (oral weekly) with folic acid, titrate to 15–25 mg. Combine with another conventional DMARD (sulfasalazine, hydroxychloroquine, leflunomide) if response inadequate.
• Bridging prednisolone short-term.
• If moderate-to-severe disease fails two DMARDs including MTX, biologics: anti-TNF (infliximab, adalimumab, etanercept), rituximab (CD20), tocilizumab (IL-6R), abatacept (CTLA-4), JAK inhibitors (tofacitinib, baricitinib).

Methotrexate monitoring: FBC, U&E, LFTs monthly for 3 months then 3-monthly. Warn about teratogenicity (stop 3 months pre-conception, both sexes) and alcohol limits. Folic acid 5 mg weekly (on a different day). Co-trimoxazole is contraindicated.

UKMLA trap: pregnant patient with RA asks about methotrexate — it's absolutely contraindicated. Switch to hydroxychloroquine or sulfasalazine (or certolizumab among biologics — minimal placental transfer).

7. Osteoarthritis — NICE Stepped Management

OA is the most common arthropathy — "wear and use." Characterised by joint pain worse with activity, stiffness <30 minutes, Heberden's nodes (DIP) and Bouchard's nodes (PIP). X-ray features: LOSS — Loss of joint space, Osteophytes, Subchondral sclerosis, Subchondral cysts.

Management (NICE NG226, 2022):

1. Non-pharmacological first: exercise (aerobic + strengthening), weight loss if BMI >25, therapeutic education, walking aids, footwear. These are first line and should be offered to everyone.
2. Pharmacological: topical NSAIDs first for knee/hand OA, then oral NSAIDs at lowest effective dose with PPI cover. Paracetamol and weak opioids should only be used in specific circumstances and for short periods (the 2022 update explicitly downgraded them).
3. Intra-articular steroids for short-term relief during flares.
4. Surgical (arthroplasty) if severely affecting quality of life — hip and knee replacements are standard.

SBA trap: "first-line management for knee OA in an obese 65-year-old" — answer is exercise + weight loss advice, not ibuprofen. The NICE 2022 update explicitly prioritised non-pharmacological measures.

8. Crystal Arthropathies: Gout vs Pseudogout

NICE NG219 gout (2022): urate-lowering therapy indicated after the first attack if serum urate is high or there are multiple attacks, tophi, or renal stones. Target serum urate <360 μmol/L (<300 if tophi). Allopurinol first-line; febuxostat if contraindicated.

Colchicine dosing: 500 micrograms 2–4 times daily until symptoms resolve, max 6 mg per course — do not repeat within 3 days. Reduce in renal impairment.

SBA trap: a patient started on allopurinol during an acute gout flare gets worse — because allopurinol paradoxically triggers flares when started during an attack. Always wait 2–4 weeks and cover with colchicine or NSAIDs.

9. SLE — ACR Criteria, Organ Involvement

SLE is the great mimic. Think of it in young women with multisystem disease: photosensitive rash, serositis, arthritis, cytopenias, nephritis, neuropsychiatric features.

Serology: ANA (positive in 95%+, highly sensitive, not specific), anti-dsDNA (specific, tracks activity, associated with lupus nephritis), anti-Smith (specific). Low C3/C4 in active disease. APS antibodies in 30%. ESR elevated, CRP often normal (CRP elevation in SLE suggests infection or serositis).

2019 EULAR/ACR criteria: entry is ANA ≥1:80, then additive criteria (fever, SLICC, arthritis, cytopenias, nephritis, neuropsych, skin, serositis).

Organ involvement to remember:

• Renal: lupus nephritis classes I–VI, biopsy required. Class III/IV → cyclophosphamide or mycophenolate + steroids.
• Neuropsychiatric: seizures, psychosis, stroke — consider APS co-morbidity.
• Haematological: AIHA, ITP, leukopenia.
• Skin: malar (butterfly) rash, discoid, photosensitivity, oral ulcers.
• Pulmonary: pleurisy, pneumonitis, pulmonary hypertension.

Management: hydroxychloroquine for everyone (disease-modifying, reduces flares and thrombosis). Steroids for flares. DMARDs (azathioprine, MMF, methotrexate, cyclophosphamide for severe renal/CNS). Biologics: belimumab, rituximab.

APS overlap: anticardiolipin, lupus anticoagulant, β2-glycoprotein I. Associated with recurrent miscarriage, DVT/PE, stroke. Management: lifelong warfarin (INR 2–3) after first thrombotic event.

10. Vasculitis Overview — ANCA Interpretation

Vasculitis is grouped by vessel size:

Large vessel:

• Giant cell arteritis (GCA): >50 years, temporal headache, jaw claudication, scalp tenderness, visual loss. ESR >50. Temporal artery biopsy. Treat empirically with 40–60 mg prednisolone (60 mg + IV if visual symptoms) before biopsy — don't wait.
• Takayasu arteritis: young Asian women, upper-limb claudication, pulse asymmetry, carotid bruit.

Medium vessel:

• Polyarteritis nodosa (PAN): associated with hepatitis B, microaneurysms on angiography, spares the lungs.
• Kawasaki disease (paediatric — covered in UKMLA paediatrics).

Small vessel (ANCA-associated):

• Granulomatosis with polyangiitis (GPA): c-ANCA/PR3, upper airway (saddle nose, nasal crusting), lungs (cavitating lesions), kidneys (pauci-immune GN).
• Microscopic polyangiitis (MPA): p-ANCA/MPO, renal + pulmonary, no granulomas.
• Eosinophilic granulomatosis with polyangiitis (EGPA, Churg-Strauss): p-ANCA, asthma + eosinophilia + vasculitis.

Small vessel (immune complex):

• IgA vasculitis (Henoch-Schönlein purpura): children, palpable purpura, arthralgia, haematuria, abdominal pain.
• Cryoglobulinaemic: HCV-associated, purpura + peripheral neuropathy.
• Behçet's disease: oral + genital ulcers + uveitis, pathergy test positive.

Management of ANCA-associated vasculitis: induction with cyclophosphamide or rituximab + high-dose steroids. Maintenance with azathioprine or methotrexate. Plasma exchange for severe renal or pulmonary haemorrhage.

11. Polymyalgia Rheumatica vs GCA Overlap

PMR and GCA share pathogenesis and frequently coexist (15–25% of PMR develops GCA; 40–60% of GCA has PMR symptoms).

PMR: >50 years, bilateral shoulder and pelvic girdle pain and stiffness, worse mornings, ESR/CRP elevated. Response to 15 mg prednisolone is diagnostic — dramatic improvement within 48–72 hours.

GCA features to screen for in every PMR patient: unilateral temporal headache, jaw claudication, scalp tenderness, visual disturbance. If any are present → escalate steroids to 40–60 mg immediately and arrange temporal artery biopsy within 7 days.

Management: PMR — prednisolone 15 mg OD, taper over 18–24 months. GCA — 40–60 mg OD (60 mg + IV methylprednisolone if visual symptoms), taper over 1–2 years. Add calcium + vitamin D + bisphosphonate for bone protection (Frax assessment). PPI if gastritis risk. Tocilizumab is now NICE-approved for GCA refractory to steroids.

UKMLA trap: a patient on prednisolone 15 mg for PMR reports a new temporal headache and jaw pain — immediately escalate to 60 mg and refer for biopsy, do not wait.

12. Ankylosing Spondylitis — Presentation, Imaging

AS is a seronegative spondyloarthropathy presenting in young men (10–30 years) with inflammatory back pain — worse mornings, better with exercise, wakes from sleep in second half of night, responds to NSAIDs within 48 hours.

Associated features (the "A" list):

• Anterior uveitis (red painful eye)
• Apical lung fibrosis
• Aortic regurgitation
• Amyloidosis
• Achilles tendonitis / enthesitis
• Atrioventricular block
• Apical kyphosis (late)

Serology: HLA-B27 positive in 90% (but HLA-B27 is in 8% of the healthy UK population — not diagnostic alone). ESR/CRP often elevated.

Imaging: sacroiliitis on X-ray (late — fusion, "bamboo spine"). MRI detects early sacroiliitis. Schober's test demonstrates reduced lumbar flexion (<5 cm increase on forward flexion from a line 10 cm above and 5 cm below L5).

Management: NSAIDs (regular, not PRN), physiotherapy, DMARDs for peripheral disease (methotrexate, sulfasalazine — don't help axial disease). Anti-TNF biologics for axial disease refractory to NSAIDs. Surveillance for cardiac and ophthalmic complications.

Other seronegative spondyloarthropathies: psoriatic arthritis (5 patterns — asymmetric oligo, symmetric poly, DIP, arthritis mutilans, spondylitic), reactive arthritis (Reiter's: "can't see, can't pee, can't climb a tree" — post-Chlamydia, Salmonella, Shigella, Yersinia, Campylobacter), enteropathic (IBD-associated).

13. Fibromyalgia — Diagnosis and NICE-Aligned Management

Fibromyalgia is a syndrome of chronic widespread pain with central sensitisation, often with fatigue, sleep disturbance, cognitive dysfunction ("fibro fog"), and comorbid depression/anxiety. It is a clinical diagnosis — no inflammatory markers elevated, no erosions on imaging.

2016 ACR criteria: widespread pain index + symptom severity score over at least 3 months, not better explained by another disorder.

Management:

• Validate diagnosis, explain central sensitisation model.
• Graded aerobic exercise — single best evidence base.
• Cognitive behavioural therapy.
• Pharmacological (adjuncts, not primary): amitriptyline 10–75 mg nocte, duloxetine, pregabalin. Avoid opioids.
• Multidisciplinary pain management programmes.

UKMLA framing: often presents in a SBA as the patient whose "normal" investigations (ANA, RF, ESR, MRI) are all reassuring but symptoms persist. Avoid the trap of ordering more invasive investigations — the answer is pain management with exercise + CBT.

14. Common Fractures: NOF, Colles, Scaphoid

Neck of femur (NOF) fracture:

• Classic: elderly woman after fall, shortened and externally rotated leg, unable to weight-bear.
• Imaging: AP + lateral hip X-ray. If normal but high suspicion, MRI.
• Classification determines surgery:
  • Intracapsular displaced → hemiarthroplasty (if frail, low demand) or total hip replacement (if previously independent, cognitively intact).
  • Intracapsular undisplaced → cannulated screws (or hemiarthroplasty if elderly).
  • Extracapsular (intertrochanteric) → dynamic hip screw.
  • Subtrochanteric → intramedullary nail.
• Management bundle: surgery within 36 hours (NICE NG124), orthogeriatric input, VTE prophylaxis, pre-op delirium screen, bone protection (DXA + bisphosphonate + calcium/D post-discharge).

Colles fracture:

• Distal radius with dorsal displacement — "dinner fork" deformity.
• Classic: postmenopausal woman FOOSH (fall on outstretched hand).
• Management: closed reduction under haematoma block or Bier's block, below-elbow backslab, repeat X-ray at 1 week. Surgical fixation for unstable fractures.
• Smith fracture: distal radius with volar displacement — reverse Colles, usually needs ORIF.

Scaphoid fracture:

• FOOSH, pain in anatomical snuffbox, pain on telescoping thumb.
• X-rays often normal initially — if clinical suspicion, immobilise in scaphoid cast and repeat X-ray or MRI at 10–14 days.
• Risk of avascular necrosis (proximal scaphoid has retrograde blood supply — displaced or proximal-pole fractures often need ORIF).
• Non-union leads to scaphoid advanced collapse (SNAC wrist).

SBA trap: "snuffbox tenderness, X-ray normal" — do not reassure. Immobilise and re-image.

15. Back-Pain Red Flags and Triage

The UKMLA-relevant back-pain triage hierarchy:

Immediate red flags (refer same day):

• Cauda equina (saddle anaesthesia, bladder/bowel dysfunction, bilateral sciatica) — MRI within 24 hours.
• Suspected spinal cord compression (progressive neurology, known cancer) — MRI whole spine within 24 hours.
• Suspected spinal infection (fever, IVDU, immunosuppression, progressive pain) — MRI + blood cultures.
• Suspected vertebral fracture (high-energy trauma, osteoporosis + minor trauma, long-term steroids) — X-ray then MRI.

Yellow/amber flags (investigate urgently 2WW):

• Unexplained weight loss, night pain, pain unrelieved by rest, history of malignancy → myeloma, metastatic disease.
• Age <20 or >50 with new-onset back pain.

Mechanical back pain (the majority):

• <6 weeks duration, no red flags → no imaging, analgesia (topical NSAIDs first, then oral NSAIDs with PPI), stay active, physiotherapy.
• Persistent >6 weeks → NICE NG59 stepped care: self-management, physiotherapy, psychological support, consider MRI only if surgical or radiological intervention is being considered.

Sciatica: L5 (dorsiflexion weakness, lateral calf paraesthesia) or S1 (plantarflexion, lateral foot) root pain. Most resolve spontaneously. MRI only if persistent beyond 4–6 weeks or progressive neurology. Surgical referral if intractable, progressive, or severely disabling.

Myeloma red flags: CRAB — Calcium elevated, Renal dysfunction, Anaemia, Bone pain. Bone profile, serum/urine electrophoresis, free light chains. Skeletal survey or whole-body MRI.

The UKMLA MSK Pattern Library

Twelve stems that reward recognition:

1. Young adult, morning back stiffness, improves with exercise → AS → MRI SI joints, NSAIDs, refer rheumatology.
2. Elderly, temporal headache, jaw claudication, ESR 85 → GCA → prednisolone 60 mg now, biopsy later.
3. Post-tibial fracture, pain disproportionate to injury, worse on passive stretch → compartment syndrome → fasciotomy.
4. Known RA patient, hot swollen knee → septic joint until proven otherwise → aspirate, IV flucloxacillin.
5. Back pain + saddle numbness + urinary retention → cauda equina → MRI within hours.
6. FOOSH, snuffbox tenderness, X-ray normal → scaphoid fracture → immobilise, re-image.
7. Post-alcohol binge, 1st MTP exquisitely painful → gout → NSAID/colchicine, allopurinol after 2–4 weeks.
8. Young woman, malar rash, arthralgia, cytopenias → SLE → ANA, anti-dsDNA, complement.
9. 50+, bilateral shoulder girdle stiffness → PMR → 15 mg prednisolone, dramatic response confirms.
10. HBV-positive, microaneurysms on angiography → PAN → immunosuppression + HBV treatment.
11. Hot diabetic foot, probe-to-bone positive → osteomyelitis → MRI, prolonged IV antibiotics.
12. Back pain + weight loss + CRAB biochemistry → myeloma → electrophoresis, skeletal imaging.

Putting It All Together

MSK questions reward a short mental tree: is this an emergency, an inflammation, or a mechanical problem? The emergencies (septic joint, cauda equina, compartment syndrome, GCA) drive the majority of high-value marks — master the recognition patterns first. The chronic rheumatology canon (RA, SLE, vasculitides, spondyloarthropathies) is predominantly a serology-pattern-matching exercise — anti-CCP, anti-dsDNA, c-ANCA, HLA-B27 each point to a short differential.

Pair this guide with our emergency presentations masterclass for cauda equina and compartment syndrome decision trees, our neurology guide for the sciatica-versus-cauda discriminator, and the prescribing safety guide for methotrexate monitoring, NSAID prescribing, and opioid-avoidance in fibromyalgia. The infectious diseases guide overlaps on septic arthritis and osteomyelitis. Finally, the NICE prioritisation principles article explains why UKMLA stems increasingly mirror the NG226 OA hierarchy and the NG219 urate-lowering thresholds.

If this pillar is doing its job, your next MSK SBA should feel like reading the labels off a specimen jar: the stem tells you the joint, the age, the inflammatory markers, and the serology, and the diagnosis and next step should be decided within twenty seconds. Ready to test yourself? Start with an MLA Prep MSK mini-mock and see which of the twelve stems you can close out on first pass.