Pitfalls in ultrasonography of hip joint synovitis in the child.

The normal and abnormal anatomy of the hip joint in childhood was evaluated by ultrasonography (US) with reference to examination technique and errors. When compared with computed tomography (CT), it was confirmed that the two sonographic echoes from the hip joint represent the femoral neck and the external surface of the capsule and that the thickness of the echo received from the capsule depends on the frequency of the transducer. Partial volume effects may simulate or increase the sonographic appearance of hip joint effusion. The normal relationship between joint capsule and femoral neck was established.