Imaging description

Snapping hip can be classified as either the external type or the internal type. The external type is readily diagnosed by clinical evaluation so medical imaging is seldom performed. The external type is usually caused by a thickened or tight iliotibial band or by thickening of the anterior edge of the gluteus maximus. This thickened edge can be associated with atrophy of the bulk of the gluteus maximus muscle.

The internal type of snapping hip is related to intra-articular pathology or to snapping of the iliopsoas tendon over the iliopectineal eminence (Figure 46.1). Ultrasound is the medical imaging test of choice if a radiograph does not demonstrate any evidence of intra-articular pathology or osteoarthritis. Dynamic US will show an abnormal, sudden jerky motion of the iliopsoas tendon when the patient repeats the hip motion that causes the snapping. If the patient is unable to voluntarily repeat the motion that causes the painful snapping, then the patient is placed in a supine position and instructed to move the hip and leg from a position of flexion, external rotation, and abduction (the so-called frog-leg position) into a position of full extension, adduction, and internal rotation. This may cause a reproduction of the painful snapping.

Static US imaging in the transverse and sagittal planes is done of the iliopsoas tendon along the course of the tendon to its attachment to the lesser trochanter. The tendon is easily seen as a hyperechoic structure surrounded by the more hypoechoic muscle tissue about the tendon (Figure 46.2).