Lesson of the Week: Septic arthritis in osteoarthritic hips

Osteoarthritis of the hip is extremely common and often runs an episodic and deteriorating course. Increased pain in affected patients is usually attributed to an exacerbation of this degenerative process, but this may miss the important development of sepsis in that joint. We have seen four such patients recently. Because of the low index of suspicion, the diagnosis was delayed in all cases. Case 1–A 67 year old woman was admitted to hospital with acute cholecystitis. Her erythrocyte sedimentation rate was 80 mm in the first hour, and her C reactive protein concentration was 19 mg/l. On the ward she complained of pain in her left hip, which was known to be osteoarthritic. This improved and she was discharged home to await cholecystectomy. She presented to the orthopaedic department three months later as an emergency with severe left hip pain; radiographs showed almost complete destruction of the femoral head. Her erythrocyte sedimentation rate was 70 mm in the first hour. An isotope bone scan was consistent with infection. The joint was aspirated under x ray screening, and culture of the fluid grew Staphylococcus aureus. She was treated with high dose intravenous flucloxacillin, but her hip remained painful, preventing mobilisation. Because of the extent of the destruction of the femoral head and the severity of the infection, she …