Septic arthritis
Septic arthritis is the purulent infection of a synovial joint. It is an emergency: untreated it causes rapid cartilage destruction, permanent loss of joint function and systemic sepsis. Emergency clinicians must recognise the condition quickly, obtain diagnostic material, stabilise the patient, and arrange urgent specialist input for drainage and definitive management.
Pathophysiology and epidemiology
Infection most commonly reaches the joint by haematogenous spread but can result from direct inoculation (penetrating injury, injection, arthroscopy) or contiguous spread from adjacent bone or soft tissue. The synovium is highly vascular and, once seeded, an intense inflammatory response with proteolytic enzymes rapidly damages cartilage.
Any age group may be affected. The knee is the commonest site, followed by the hip, shoulder, ankle and small joints. Prosthetic and previously diseased joints (for example rheumatoid arthritis) carry higher risk.
Predisposing factors Common risk factors include:
- Pre‑existing joint disease such as rheumatoid arthritis or osteoarthritis.
- Presence of a prosthetic joint.
- Recent joint surgery, recent intra‑articular injection or penetrating trauma (including animal or human bites).
- Intravenous drug use.
- Immunosuppression, including diabetes, chronic corticosteroid therapy, HIV infection or malignancy.
- Advanced age or recent systemic sepsis.
Causative organisms
- Staphylococcus aureus is the most frequent pathogen, including MRSA where prevalent.