Abstract
Although femoroacetabular impingement (FAI) is traditionally considered an intra-articular phenomenon, the result of abutment between the femoral head and/or neck and the acetabular rim, there are unique and relatively uncommon patterns of pathologic extra-articular hip impingement that can mimic the clinical presentation and clinical findings of traditional FAI. Anterior inferior iliac spine (AIIS) or “subspine” impingement may occur as a consequence of an abnormally anterior or distal prominence of the AIIS that may be developmental, posttraumatic, or the result of high range of motion (ROM) activities. This type of impingement can crush the capsule, labrum, and rectus femoris between the AIIS and distal femoral neck in straight hip flexion. Greater trochanteric/pelvic impingement is quite complex and can be further divided into three unique anatomic patterns. Anterior greater trochanteric–pelvic impingement is the result of impingement between the anterior hip soft tissue structures or the anterior facet/greater trochanter and anterolateral rim/lateral AIIS and pelvis when the hip is flexed, internally rotated, and abducted. This can occur in association with a prominent greater trochanter, short femoral neck, relative femoral retrotorsion, and high ROM activities. Lateral greater trochanteric–pelvic impingement is the result of impingement between an abnormally prominent or a high riding greater trochanter with a short femoral neck and the lateral pelvis when the hip is abducted. This type of impingement is characteristic of a Perthes-like hip and, in extreme cases, can be associated with severe leg length discrepancy (and abductor muscle dysfunction). Posterior greater trochanteric–pelvic/ischiofemoral impingement is the result of impingement of the quadratus femoris and/or proximal hamstring tendons between the lesser trochanter or posterior proximal femur and intertrochanteric line and the ischial tuberosity when the hip is extended and external rotated (ER). This can occur in association with deformities of the ischial tuberosity caused by prior avulsion fractures, lesser trochanteric overgrowth, extreme coxa valga, femoral antetorsion, complex proximal femoral developmental deformities, and activities requiring high degrees of extension and external rotation. A thorough understanding of these unique patterns of impingement, their clinical presentations, and complex treatment options can help in optimizing outcomes and minimizing complications in this very challenging patient population.
Keywords
hip impingement - AIIS - subspine
