Recent evidence suggests that abnormalities in the shape of the hip joint may be the primary cause of activity-related hip pain in young adults (late teens to forties) and the subsequent development of osteoarthritis in adults.
These abnormalities are manifest as acetabular (or socket) deficiency or malorientation, or deficiency or malorientation of the femur. Most commonly, a combination of the two is present. Current hip preservation surgical techniques are focused on the correction of these abnormalities, alleviation of hip pain, and possibly slowing the process of hip osteoarthritis.
Hip dysplasia, sometimes referred to as DDH (Developmental Dysplasia of the Hip), is a relatively common abnormality in the shape of the hip joint. DDH is the most common cause of hip pain in adults and is the most common cause of osteoarthritis of the hip. In its most common form, DDH is a shallow acetabulum (or socket). In a separate, but common and often associated form, the socket is oriented out to the side or toward the back (retroversion) as opposed to its more common orientation of slightly toward the front (anteversion) (Fig. 1). When the socket is shallow, there is a lack of coverage of the femoral head (or ball) and this increases the load seen on the rim of the socket, causing mechanical breakdown of the cartilage (arthritis) (Fig. 2).
Femoroacetabular impingement (hip impingement) is a process that goes on in the hip joint due to abnormal shape of the ball and socket. Often this presents as pain with sitting or deep flexion activities. Hip impingement may be caused by an improperly oriented acetabulum or an abnormal shape to the front of the femoral head and neck (at the top of the thigh bone), or in about 80% of cases, a combination of both. The two types of hip impingement are cam and pincer and are illustrated in Figure 3. Depending upon the dominant type of deformity, damage, fraying, or detachment of the hip socket cartilage occurs as a result of this process over time.
The hip labrum is the gristle-like lining of the rim of the acetabulum (hip socket). The labrum functions to stabilize the hip joint and maintain proper mechanics of the hip. A tear of the labrum can often cause pain the front of the hip, sometimes shooting down the thigh. The pain can be associated with a catching or locking. Often these symptoms occur when the hip is changing positions. If the labrum tears, it is usually associated with an underlying abnormality of the shape of the hip joint.
There are a number of surgical techniques directed at preserving the hip joint and delaying the need for hip replacement. These include surgical dislocation and debridement, osteochondroplasty, hip arthroscopy, and redirectional acetabular (socket) osteotomy. As the techniques develop, the understanding of hip pathology in the young adult has become an important focus of orthopaedic surgeons. Surgical intervention should be focused on correction of the underlying shape abnormality as well as the cartilage and labral damage.