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
