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This is a clinician-written, evidence-based summary aligned to the 2026 MLA Content Map. It is intended for medical students and junior doctors preparing for the UKMLA. Always cross-reference with NICE guidance, local protocols, and clinical judgement.
The Bottom Line
- S. aureus is the most common causative organism in all age groups (>50%)
- Acute haematogenous: children (metaphysis of long bones). Contiguous/secondary: adults (diabetic foot, post-surgery, trauma)
- MRI is the imaging modality of choice — high sensitivity and specificity
- Blood cultures and bone biopsy/culture for microbiological diagnosis before antibiotics if possible
- Treatment: prolonged IV antibiotics (4–6 weeks) ± surgical debridement for chronic disease
Overview
Osteomyelitis is infection of bone caused by bacteria (most commonly S. aureus), fungi, or mycobacteria. It is classified by route of infection: haematogenous (bloodstream — commonest in children, affecting metaphysis of long bones), contiguous spread (from adjacent soft tissue infection, e.g. diabetic foot ulcer), and direct inoculation (open fracture, surgical). Chronic osteomyelitis develops when acute infection is inadequately treated, forming sequestra (dead bone) surrounded by involucrum (new reactive bone). Chronic osteomyelitis is extremely difficult to eradicate and may require surgery.
Epidemiology
Haematogenous osteomyelitis predominantly affects children (boys > girls, mean age 5 years) and involves long bones (tibia, femur, humerus). In adults, vertebral osteomyelitis (spondylodiscitis) is the most common haematogenous form. Contiguous osteomyelitis is most commonly associated with diabetic foot infections, pressure ulcers, and post-surgical infections. S. aureus causes >50% of cases across all age groups. Other organisms: Streptococcus, Enterobacteriaceae (GU source), Salmonella (sickle cell disease), Pseudomonas (IVDU, penetrating injury).
Clinical Features
Symptoms
Localised bone pain — deep, constant, worsening
Fever and malaise (may be absent in chronic osteomyelitis)
Reluctance to use or move affected limb (children)
Non-healing wound or ulcer overlying bone (contiguous — especially diabetic foot)
Back pain with fever (vertebral osteomyelitis/spondylodiscitis)
Signs
Localised tenderness, warmth, swelling over affected bone
Reduced range of movement of adjacent joint
Draining sinus tract (chronic osteomyelitis — discharge of pus through skin)
Probe-to-bone test positive in diabetic foot ulcer (probe through ulcer contacts bone — high PPV for osteomyelitis)
Investigations
First-line
BloodsFBC (leucocytosis), CRP (raised — most useful for monitoring response), ESR (raised — takes longer to normalise), blood cultures (positive in ~50% of haematogenous)
MRI affected areaInvestigation of choice — sensitivity ~90%, specificity ~80%. Shows bone marrow oedema, soft tissue involvement, abscess formation, extent of disease
Second-line
X-rayUsually normal in first 10–14 days (lags behind clinical picture). Later: periosteal reaction, lytic destruction, sequestrum, involucrum
Bone biopsy and cultureGold standard for microbiological diagnosis — ideally before antibiotics. CT-guided or surgical biopsy. Crucial for targeted antibiotic therapy
Specialist
Labelled white cell scan or PET-CTIf MRI inconclusive or to distinguish infection from other pathology (e.g. Charcot neuroarthropathy vs osteomyelitis in diabetic foot)
Management
NICE CKS and BOA/BSAC guidance1
Acute osteomyelitis
- IV antibiotics: flucloxacillin 2 g QDS (covers S. aureus). If MRSA risk: vancomycin or teicoplanin
- IV for initial 2–4 weeks, then oral step-down (total 4–6 weeks minimum)
- Blood cultures and ideally bone biopsy BEFORE antibiotics
- Surgical drainage if abscess (subperiosteal or intraosseous)
2
Chronic osteomyelitis
- Surgical debridement: removal of sequestrum (dead bone) and infected tissue
- Prolonged antibiotic therapy (6–12 weeks or longer) guided by bone culture sensitivities
- Dead space management: antibiotic-loaded cement beads, flap coverage
- May require multiple operations — recurrence rate is high
3
Vertebral osteomyelitis (spondylodiscitis)
- CT-guided biopsy for culture before antibiotics
- IV antibiotics for 6 weeks minimum (often 12 weeks total)
- Spinal immobilisation if instability. Surgical decompression if epidural abscess with neurological deficit
- Screen for endocarditis if S. aureus bacteraemia
Complications
- Chronic osteomyelitis: If acute infection inadequately treated — sequestrum formation, draining sinuses
- Pathological fracture: Through weakened infected bone
- Septicaemia: Haematogenous spread — can cause septic arthritis, endocarditis
- Growth plate damage (children): Infection crossing the physis → growth arrest, limb length discrepancy
- Amputation: Rarely required for uncontrollable chronic infection (especially diabetic foot)
- Squamous cell carcinoma: Rare long-term complication of chronic draining sinuses (Marjolin ulcer)
UKMLA Exam Tips
- 1S. aureus is the most common cause in ALL age groups
- 2Sickle cell disease: Salmonella osteomyelitis (classic exam association, though S. aureus is still the most common overall)
- 3MRI is the imaging of choice — X-ray may be normal for first 10–14 days
- 4Probe-to-bone test: positive in diabetic foot ulcer = high PPV for osteomyelitis
- 5Haematogenous in children: affects the METAPHYSIS (rich blood supply with sinusoidal capillaries)
- 6Sequestrum = dead bone; Involucrum = new bone forming around it (chronic osteomyelitis)
- 7Vertebral osteomyelitis: back pain + fever + raised CRP — get MRI spine and blood cultures
practicetest your knowledge on osteomyelitisApply what you've learnt with UKMLA-style questions from the iatroX Q-Bank — musculoskeletal and beyond.
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