Osteomyelitis

Bacteria can penetrate bone from a contiguous focus of infection (e.g. a diabetic foot ulcer or local injury) or by haematogenous spread. Osteomyelitis is most commonly caused by Staphylococcus aureus, β‎-haemolytic streptococci, and—in some situations—aerobic Gram-negative rods. An acute inflammatory response causes oedema within bone and soft tissue, and thrombosis in vessels that can result in bone infarction. Pus may form within cancellous bone and beneath the periosteum, stripping it from the bone and leading to extensive necrosis that sometimes involves an entire bone. The process may become chronic and relapsing. Definitive diagnosis can only be confirmed with culture of bacteria from representative bone samples, supported by histological evidence of inflammation. This cannot be achieved in all cases and diagnosis is commonly made on the basis of clinical features and imaging. MRI is the standard and best method.