Septic Arthritis is also known as infectious arthritis, bacterial, or fungal arthritis. It is the purulent invasion of a joint by an infectious agent which produces arthritis. The condition is an inflammation of a joint that's caused by infection. Typically, septic arthritis affects one large joint in the body, such as the knee or hip. Less frequently, septic arthritis can affect multiple joints. Septic arthritis is considered a medical emergency. If untreated, it may destroy the joint in a period of days. The infection may also spread to other parts of the body.
Pathophysiology: The major consequence of bacterial invasion is damage to articular cartilage. This may be due to the particular organism's pathologic properties, such as the chondrocyte proteases of S aureus, as well as to the host's polymorphonuclear leukocytes response. The cells stimulate synthesis of cytokines and other inflammatory products, resulting in the hydrolysis of essential collagen and proteoglycans. Infection with N gonorrhoeae induces a relatively mild influx of white blood cells (WBCs) into the joint, explaining, in part, the minimal joint destruction observed with infection with this organism relative to destruction associated with S aureus infection.
We estimate the prevalence of nongonococcal septic arthritis in adults presenting to the evidence-based Diagnostics with acute monoarticular joint complaints to be approximately 27%. With the exception of recent joint surgery or cellulitis overlying a prosthetic knee or hip, the history, physical examination, and routine blood tests do not distinguish acute septic arthritis from other forms of arthritis. In other words, neither the presence nor the absence of these findings significantly changes the probability of septic arthritis. On the other hand, a synovial white blood cell count of >50 × 109/L can increase the probability of septic arthritis, while a synovial white blood cell count from 0 to 25 × 109/L can reduce the probability of septic arthritis, and values of 25 × 109 to 50 × 109/L require additional testing and perhaps empiric antibiotics pending definitive culture results. Future prospective trials are needed to understand the sensitivity, specificity, and positive and negative likelihood ratios for elements of the history and physical examination and point-of-care inflammatory synovial markers such as lactate, which may be useful to rule in or rule out septic arthritis. In the meantime, clinicians should be aware of the risk factors for nongonococcal septic arthritis in expeditiously selecting appropriate diagnostic and therapeutic options while consulting orthopedic surgery for early management when clinical evaluation remains less than definitive.