Acute septic arthritis

Most septic joints develop as a result of hematogenous seeding of the vascular synovial membrane due to a bacteremic episode (86, 113). Although a rare cause, acute septic arthritis may also occur as a result of joint aspiration or local cortico-steroid joint injection (74, 86). In addition, bacterial arthritis may arise secondary to penetrating trauma (such as human or animal bite or nail puncture) or after trauma to a joint without an obvious break in the skin. The direct introduction of bacteria during joint surgery has increasingly been a source of bacterial arthritis, particularly in association with knee and hip arthroplasties. When a bone infection breaks through the outer cortex and into the intracapsular region, a joint infection may also result, especially in children (9, 117). In infants, small capillaries cross the epiphyseal growth plate and permit extension of infection into the epiphysis and joint space (22). In children older than 1 year, osteomyelitis infection presumably starts in the metaphyseal sinusoidal veins and is usually contained by the growth plate. The joint is spared unless the metaphysis is intracapsular. The infection spreads laterally, where it breaks through the cortex and lifts the loose periosteum to form a subperiosteal abscess. In adults, the growth plate has resorbed and the infection may again extend to the joint spaces.