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1. What are the joints most commonly affected by septic arthritis? The most common site is the knee (41%), followed by the hip (23%), ankle (14%), elbow (12%), wrist (4%), and shoulder (4%). The remaining joints (of the hands and feet as well as the sacroiliac and acromioclavicular joints) comprise the remaining 2%. Classic suppurative septic arthritis involves a single joint in 94% of the cases.

2. What is the basic pathophysiology of septic arthritis? Bacteria can be introduced into the joint through transient bacteremia, direct inoculation (ie, puncture wound), or local extension (of osteomyelitis). Once a sufficient inoculum has been introduced into the joint, the bacteria colonize the vascular synovium and" culture tube-like" environment of the joint. Some bacteria (eg, Staphylococcus and Pseudomonas) have an affinity for cartilage and directly attach to the chondral surface. Bacterial proliferation is possible owing to the relatively nonimmunogenic environment of the normal joint.