Osteomyelitis
Bone infection arising from haematogenous seeding, contiguous spread, or direct inoculation. *Staphylococcus aureus* is the commonest organism in adults. MRI is the imaging modality of choice; treatment combines prolonged antibiotics and sometimes surgical debridement.
Key Facts
Key points
- Acute haematogenous osteomyelitis: children (metaphysis) and adults (vertebral).
- MRI is most sensitive for early bone oedema; plain radiographs lag by 10–14 days.
- Blood cultures may be positive; bone biopsy for microbiology where safe/practical guides therapy.
- Flucloxacillin 2 g IV 4-hourly for MSSA (typical 4–6 weeks total — IV then oral switch per clinical response).
- Vancomycin IV if MRSA risk; clindamycin 600 mg IV QDS oral step-down alternative for penicillin allergy (confirm susceptibility).
- Diabetic foot osteomyelitis: polymicrobial; often co-amoxiclav or piperacillin/tazobactam; surgical offloading and revascularisation are key.
Overview
Classification
- Acute vs chronic (symptoms >6 weeks suggests chronic).
- Haematogenous vs contiguous (adjacent soft-tissue/decubitus) vs post-operative/traumatic.
Risk factors
Diabetes mellitus, peripheral vascular disease, immunosuppression, IV drug use, prosthetic material.
Pathophysiology
Bacterial invasion causes inflammatory bone destruction; sequestrum formation in chronic disease impairs antibiotic penetration.
Clinical Presentation
Presentation
- Local pain, swelling, reduced weight-bearing; fever may be absent, especially in diabetes.
Vertebral osteomyelitis
- Back pain, focal tenderness; epidural abscess may cause neurological deficit — urgent MRI.
Red flags
- Neurological signs, sepsis, spreading soft-tissue infection — emergency assessment.
Differential Diagnosis
| Condition | Clues |
|---|---|
| Cellulitis/abscess without bone involvement | MRI negative for marrow oedema |
| Charcot neuro-osteoarthropathy | Warm swollen foot, neuropathy, different MRI pattern |
| Malignancy/bone metastasis | Systemic symptoms, imaging pattern |
| Fracture/stress injury | History of trauma, linear marrow oedema |
Diagnosis / Investigation
Imaging
- MRI first-line for suspected osteomyelitis.
- Plain radiographs if chronic changes suspected or MRI unavailable.
- WBC-labelled scan occasionally if MRI contraindicated.
Microbiology
- Blood cultures before antibiotics.
- Bone/deep tissue culture (avoid superficial swabs in diabetic foot).
Bloods
- CRP, ESR, FBC, HbA1c if diabetes.
Management
Acute MSSA (example adult regimen — follow local protocol)
- Flucloxacillin 2 g IV 6-hourly until stable, then oral flucloxacillin 500 mg–1 g QDS to complete 4–6 weeks typical total.
- MRSA: vancomycin IV (target trough 15–20 mg/L for serious infections per local guidance) or daptomycin 6–10 mg/kg OD (not pneumonia).
Gram-negative / polymicrobial (diabetic foot)
- Piperacillin/tazobactam 4.5 g TDS IV or co-amoxiclav if mild and susceptible.
- Add metronidazole 500 mg TDS if anaerobic concern.
Chronic staphylococcal (oral combination — specialist)
- Rifampicin 300–450 mg BD plus fusidic acid or flucloxacillin — never rifampicin monotherapy; check interactions.
Surgery
- Drain abscess; remove necrotic bone/hardware; revascularisation when ischaemic.
Prognosis
Acute haematogenous osteomyelitis in children often resolves with antibiotics alone. Adult vertebral and diabetic foot infections have higher morbidity and recurrence; multidisciplinary foot care reduces amputation risk.
Other Relevant Information
OPAT
Early switch to oral therapy is standard when clinically appropriate and microbiology supports oral agents.