Osteomyelitis
This is a condition where there's inflammation in bone and bone marrow, usually due to bacterial infection. The most common mode of infection is haematogenous (via blood), but there can also be direct contamination of the bone e.g. during surgery or trauma.
The most common causative organism is Staph aureus.
Risk factors:
Open fractures
Orthopaedic surgery, particularly with prosthetic joint
Diabetes Mellitus, particularly those with diabetic foot ulcers
Peripheral arterial disease
IVDU
Immunosuppression
Presentation
Fever
Pain and tenderness
Erythema
Swelling
Investigations
Bloods – WCC, CRP, ESR
Blood cultures
Bone biopsy and culture
Imaging - XR, MRI
XR may show signs of bony destruction, but MRI is much more sensitive
Management
Surgical debridement of infected bone and tissues
Abx – Flucloxacillin + Fusidic acid/Rifampicin
N.B. Staph aureus is the most common cause of acute osteomyelitis, which is why Flucloxacillin is a good choice of empirical treatment.
The Fusidic acid is very important to give for 3 important reasons:
Synergistic effect - Fusidic acid and flucloxacillin work synergistically against staph aureus, therefore both together is more effective than one alone. Flucloxacillin is a β-lactam antibiotic effective against staphylococcal infections, but the addition of fusidic acid can enhance its efficacy, especially in difficult-to-treat infections.
Coverage of Deep-Seated Infections - In serious infections like osteomyelitis or infected prosthetic devices, fusidic acid can penetrate deeper tissues, including bone and biofilm, where flucloxacillin may have limited penetration. The combination helps ensure that both surface and deeper tissues are adequately treated.
Broader Spectrum - While flucloxacillin is effective against gram-positive organisms like staph aureus, fusidic acid may offer a broader range of activity against strains that have lower sensitivity to β-lactam antibiotics, providing broader coverage in complex or mixed infections.
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