Subspine impingement of the hip

The anterior inferior iliac spine (supine or anterior inferior iliac spine) is a bony prominence located on the wing of the ilium. It lies deep beneath the soft tissues, in the area where the ilium passes into the hip joint. Three types of anterior inferior iliac spine have been described:
Type I: the wall of the ilium is smooth and shows no bony prominence between the anterior inferior iliac spine and the acetabular rim.
Type II: the bony prominence extends from the lower part of the anterior inferior iliac spine as far as the acetabular rim.
Type III: the anterior inferior iliac spine has a spur-like appearance and extends below the level of the acetabular rim.
The shape of the anterior inferior iliac spine is thought to be related to the range of motion of the hip, and any bony prominence may cause the bones to rub against or impinge on one another (impingement).
Impingement of the hip was initially thought to be caused by abnormal bony prominences between the femoral head and the acetabulum within the hip joint. It now appears, however, that even bony structures outside the joint can lead to rubbing or impingement. Subspine impingement, as it arises with type II and type III anterior inferior iliac spines, is an important condition and may cause a reduction in internal rotation and flexion of the hip, and therefore requires surgical correction.
The symptoms in such patients do not differ greatly from those of femoroacetabular impingement; that is, they include pain, restricted range of motion and inflammation of the synovium. The diagnosis of the condition is chiefly clinical, but it can be investigated further with plain radiographs, computed tomography and magnetic resonance imaging of the hip.
The treatment of subspine impingement depends on the severity of the symptoms. In cases that do not settle with conservative treatment, arthroscopic decompression is recommended — that is, the technique of removing part of the anterior inferior iliac spine during hip arthroscopy.