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that there are regional variations in virulence factors or causative organisms in septic arthritis of which clinicians should be aware Often, based on clinical findings, a physician can make a diagnosis of transient synovitis without the need for laboratory testing or arthrocentesis In more equivocal cases, inflammatory markers may be helpful and Lyme testing should be considered Inflammatory markers are usually elevated in patients with osteomyelitis, as well In contrast to those with septic arthritis, children with osteomyelitis have a more subacute onset of pain, are less likely to be febrile, have focal bony tenderness, will have greater range of motion at the joint, and may not have signs of joint inflammation Legg–Calvé–Perthes disease, a condition of uncertain cause, occurs overwhelmingly in boys, with an onset between and years of age The pain, which may be localized to the hip or referred to the thigh or knee, is insidious in onset The aseptic or avascular necrosis of the femoral head will be manifest on plain radiographs as a small, osteopenic femoral head with a widened joint space although films obtained early in the clinical course may be normal Polyarthritis Historical and physical examination findings help narrow the choices among the many causes of polyarthritis and fever ( Tables 60.4 and 60.5 ) The ill-appearing adolescent with migratory arthritis, tenosynovitis involving the extensor tendons of the wrist or ankle, and scattered crops of vesiculopustules should be strongly suspected for gonococcal arthritis This occurs three to five times more often in girls, often during menstruation Of note, patients may report lower abdominal pain or vaginal discharge concurrently, and cultures of blood and synovial fluid are typically negative The highest yield for establishing the diagnosis is by Gram stain of the skin lesions or by recovering the organism from the cervix, rectum, or throat