Iliopsoas musculotendinous unit.

Hip pain is a common condition with many etiologies, and the workup often includes imaging. The iliopsoas musculotendinous unit is becoming more frequently recognized as the culprit for hip pain, partially due to the increase in athletic activity in the general population as well as to the increased demand in professional sports. Iliopsoas tendon injuries are also seen in the elderly population and documented as occurring following total hip replacement. Iliopsoas diseases, often overlooked as a cause of hip pain, include tendinosis, snapping tendon, bursitis, tears, and avulsion injuries. This article reviews the normal magnetic resonance imaging and sonographic anatomy of the iliopsoas musculotendinous unit and the imaging characteristics of diseases that involve the iliopsoas musculotendinous unit. We review the causes of a snapping hip and the role of sonography in evaluating and guiding treatment of the snapping iliopsoas tendon.