Hip sonography is the study of choice for diagnosis of hip problems in the
first 6 months of life. Developmental dysplasia can be classified according
to severity, and management can be guided by serial sonograms. Other conge
nital disorders are less common but can be evaluated. The painful hip in ol
der children may be caused by a variety of conditions that initially have n
egative radiographs. Ultrasound is used to document the presence of a joint
effusion and guide aspiration. Specific diagnoses cannot be made from the
sonographic appearance of joint fluid.