Current Evidence Bacteria gain entry to the joint space through one of three means The highly vascular synovium is most commonly infected through hematogenous seeding The role of local injury in predisposing joints to infection by this means is unclear Organisms from adjacent areas of infection may invade the joint, or direct inoculation can occur through penetrating injuries Infection secondary to penetrating objects may be delayed from the actual time of injury so that external wounds may be small or healed at the time of presentation Adjacent osteomyelitis is present in up to 10% of cases Eighty percent to 90% of septic joints occur in the lower extremities The knee and hip are most commonly affected The same distribution is found in the preambulatory child Infections involve only a single joint in greater than 90% of cases Multifocal infections are more common in neonates and infections with Neisseria species Pressure elevation within the minimally distensible joint capsule can compromise vascular flow, resulting in ischemic injury to the bone and cartilage This is a particular concern in the hip, where avascular necrosis of the femoral head is a well-described complication of septic arthritis Prognosis is worse in children younger than year, with involvement of the hip joint, with delay to the initiation of therapy, and with infection by S aureus Clinical Considerations Clinical Recognition Septic arthritis occurs in all ages Pain is the most common presenting complaint in the child with a septic joint Because of the predominance of septic arthritis in the lower extremities, the younger child often presents with a limp, abnormal gait, or inability to bear weight Referred pain from the hip may manifest as groin, thigh, or knee pain Swelling or redness of a joint is often a late finding but can be the primary reason for the patient to seek medical care The neonate or young infant with a septic joint may display fever, fussiness, pain with handling, or lack of movement of a limb Recent traumatic events not adequately explain these findings Patients with a prior history of a rheumatologic condition or invasive procedures involving the joint are more likely to have an alternate cause for their joint pain Triage Patients with complaints of joint pain and/or fever, limited range of motion of a joint, joint swelling or limp are typically categorized as urgent The patient with