Abstract
There are a variety of causes for hip pain in children, including slipped capital femoral epiphysis (SCFE), toxic synovitis, septic arthritis, Perthes disease, fracture, and juvenile rheumatoid arthritis. Several of these processes can result in hip joint effusions. Although radiography is initially performed and is often diagnostic, the plain radiograph may be normal in the presence of a small joint effusion. Sonography can be used to determine whether an effusion is present and when deemed clinically appropriate, to guide a diagnostic or therapeutic arthrocentesis. When patients show signs of sepsis and effusion, an ultrasound-guided arthrocentesis can help differentiate between septic arthritis and toxic synovitis. In the evaluation of difficult cases, a bone scan or magnetic resonance imaging may be helpful to exclude the possibility of underlying osteomyelitis.