Septic arthritis

Definition/diagnostic criteria Septic arthritis, a serious joint infection, is characterised by suppurative inflammation within a joint space. It most commonly results from haematogenous spread but can also occur due to direct spread from a penetrating wound or a neighbouring infection such as chronic osteomyelitis. The condition is often monoarticular, predominantly affecting the knee and hip, although any joint can be involved.

In infants, there can be multiple joint involvement, and septic arthritis of the hip may present as knee pain and vice versa​​.

Epidemiology Vulnerable groups include children, premature neonates, the elderly, and those with an immune-suppressed status. Individuals with rheumatoid arthritis, weakened immune systems, recent joint surgery, artificial joints, intravenous drug use, and sexually transmitted infections like gonorrhoea are also at heightened risk​​​​.

Diagnosis
Clinical features: Symptoms suggestive of septic arthritis include:

• A short history of a hot, swollen and tender joint, with restricted movement.
• Severe joint pain, usually in just one joint, swelling around a joint, changes in skin colour around a joint, and general malaise with high temperature are common presentations​​​​.

Investigations: The mainstay of diagnosis involves aspirating synovial fluid for Gram staining and culture before initiating antibiotic treatment. Blood cultures, white cell count (WCC), erythrocyte sedimentation rate (ESR), and C-reactive protein (CRP) levels are also indicative, although their absence does not exclude septic arthritis. Urea, electrolytes, and liver function tests are important for detecting end-organ damage​​​​.

Treatment
Antibiotics: Immediate initiation of antibiotic therapy is crucial. Gram staining of synovial fluid is critical for early, targeted antibiotic therapy. Common pathogens in the UK include Staphylococcus aureus or streptococci. The choice of antibiotics should reflect the likely pathogens and be amended based on culture results. The typical regimen involves intravenous antibiotics for up to two weeks or until signs improve, then oral antibiotics for around four weeks​​.

Joint drainage and surgical options: Aspiration of the septic joint to dryness is recommended, using either a closed needle approach or arthroscopically. If the response to closed needle aspiration is unsatisfactory or pus is thick, arthroscopic aspiration should be used for biopsy, repeat culture, washout, and potentially debridement.

In suspected hip sepsis, early orthopaedic consultation is advised due to the risks of avascular necrosis and chondrolysis​​.

Prognosis With timely and appropriate treatment, a full recovery is possible. However, if left untreated, septic arthritis can lead to more serious complications​​.