11.5 Septic arthritis

Septic arthritis indicates inflammation of the joint due to the invading organism. Bacteria within the joint space in adult septic arthritis may occur from haematogenous spread but most commonly occurs due to direct inoculation either from trauma or iatrogenic joint penetration, for example, intra-articular injection or arthroscopy. Contiguous osteomyelitis can also spread to local joints. Once again a high index of suspicion is required in the elderly or immunocompromised with a swollen joint as other symptoms may be reduced. Associated conditions including rheumatoid arthritis and other seronegative arthropathies predispose patients to septic arthritis, especially when joint aspiration and intra-articular steroid injections are undertaken.

Following infection, synovial infiltration with inflammatory cells, initially with polymorphonuclear leucocytes, are replaced with chronic mononuclear cells by 3 weeks. The inflammatory response results in an effusion which can become large enough to result in joint subluxation or even dislocation. This will also eventually result in articular cartilage destruction although the specific mechanism of this remains unknown—it is thought to be destructive enzymes within the exudate. This occurs as early as 4–6 days following initial infection, with total joint destruction by 4 weeks.

The natural history of septic arthritis is known to result in eventual joint destruction and therefore this is an orthopaedic emergency which requires immediate treatment.

The principles of treatment include joint drainage and wash out. Systemic antibiotics are administered and the joint is splinted in a position of function. A drain can be placed to allow further drainage.

Drainage can involve formal joint arthrotomy and lavage or repeated joint aspiration. Arthroscopic lavage can also be considered in knee, ankle, shoulder, and elbow infection. My personal choice is open surgical drainage and wash out with saline.

If systemic and local symptoms do not resolve further, washout including formal open arthrotomy and debridement may be required within 24–48h following initial surgery.

The duration of antibiotics should continue for 4–6 weeks even if symptoms resolve quickly. After cessation of infection, treatment is concentrated on rehabilitation and restoration of joint function. Continual passive motion may inhibit adhesions and promote better nutrition to the cartilage. Residual joint deformity may respond to traction, serial casting, or dynamic splints. In the chronic ankylosed deformity, corrective osteotomy can place the limb in an optimal functional position.