Section 3. Hip Preservation and Replacement Hip Pain in Young Adults Femoroacetabular Impingement Fereidoon M. Jaberi, MD,* and Javad Parvizi, MD, FRCSy Abstract: Femoroacetabular impingement is a more recently noticed cause of hip pain in young patients, and early diagnosis and treatment are critical to prevent development of osteoarthritis and/or delay the need for a more radical treatment option such as arthroplasty surgery. Two general types of femoroacetabular impingement have been described. In the cam impingement, the femoral deformity, usually a bump on the head-and-neck junction, impinges on the acetabular rim. The pincer type of impingement is caused by the deformity on the acetabular side, which may be a deep socket, or an acetabular overcoverage due to retroversion that creates an obstacle for flexion and internal rotation. This article attempts to examine the underlying pathogenesis and discusses diagnostic and treatment modalities. Key words: femoroacetabular impingement, labrum, hip, pain, young adult. �� 2007 Elsevier Inc. All rights reserved. Axial overload as a factor for the onset of osteoar- thritis (OA) of the hip fails to explain the develop- ment of degenerative arthritis in young patients with a normal skeleton. Degenerative joint arthritis in young patients is almost universally associated with an underlying mechanical disorder generally it is attributed to concentric or eccentric overload. This mechanical compromise predisposes the joint to dynamic instability, localized joint overload, impingement, or a combination of these problems. Femoroacetabular impingement (FAI) has been suggested as a potential mechanism for the devel- opment of early osteoarthritis for most nondysplas- tic hips [1]. The concept focuses more on motion than on axial loading of the hip. In patients with abnormal morphological features of the acetabulum and/or the femoral neck, less motion is required before abutment around the hip occurs. Traditional diagnostic modalities fail to reveal the etiology of subtle changes in the femoroacetabular spatial relationship, which leads to mechanical blockage or impingement in the terminal range of motion of hip [1]. Although previously described [2,3] this recently repopularized phenomenon is more com- mon in active young adults and should be con- sidered as a syndrome because of the multiplicity of the underlying etiologies. Pathologic Anatomy The condition occurs either as a result of morphological abnormality of the femoral head, so-called cam impingement, or the acetabular side, so-called pincer impingement. It is, however, important to point out that distinction between these is not always clear because abnormality of both the acetabulum and the femoral head-neck junction may be present in some patients [4]. From the *Department of Orthopaedic Surgery, Shiraz University of Medical Sciences, Shiraz, Iran and yRothman Institute at Thomas Jefferson Hospital, Philadelphia, Pennsylvania. Submitted February 28, 2007 accepted May 24, 2007. JP received funding for research from Stryker Orthopaedics, Mahwah, NJ. Reprint requests: Javad Parvizi MD, FRCS, Rothman Institute at Thomas Jefferson University Hospital, 925 Chestnut Street, Philadelphia, PA 19107. �� 2007 Elsevier Inc. All rights reserved. 0883-5403/07/1906-0004$32.00/0 doi:10.1016/j.arth.2007.05.039 37 The Journal of Arthroplasty Vol. 22 No. 7 Suppl. 3 2007

Cam impingement is more common in young males with morphological abnormalities involving the femoral head [3,5]. It is caused by the jamming of an abnormal femoral head with increasing radius into the acetabulum during forceful flexion. It has been associated with an elliptical femoral head, slipped capital femoral epiphysis, Legg-Calve- Perthes disease, adult osteonecrosis, and malunited femoral neck fractures. The shearing force results in an outside-in directed detachment of the acetabular rim cartilage anterosuperiorly from the labrum and subchondral bone, which in turn leads to avulsion of intact labrum. A significant reduction in the mean femoral anteversion and mean head-neck offset in the anterior aspect of the femoral neck has been reported in these patients [1]. Pincer impingement is a linear contact or abutment between the acetabular rim and the femoral head junction. The pathology is on the acetabular side, and the first damaged structure is the acetabular labrum. Chon- dral lesions in pincer impingement are usually limited and benign, but repeated impact on the labrum results in labral degeneration and intrasub- stance ganglion formation or ossification of the acetabular rim, leading to progressive worsening of the overcoverage. It has been associated with acetabular retroversion, coxa profunda and protrusio acetabuli, iatrogenic overcorrection for retroversion in dysplastic hips, coxa vara, and os acetabuli. It is more common in middle-aged women with mor- phological abnormalities of the acetabulum [1-3,5]. Although the mentioned conditions may give rise to FAI, most cases are idiopathic. Clinical Presentation Labral lesions occur in almost all cases and are the most common presenting finding. The labral tear is a secondary issue occurring as a result of shearing or abutment forces that occur during motion. Slow onset of initially intermittent groin pain after a minor trauma, which gradually exacerbates by athletic activity or prolonged walk- ing, is the typical presentation. Mechanical symp- toms such as locking, catching, or clicking are common with labral tears, but these are nonspe- cific for the disorder. Chondral lesions, labral lesions, or both may be the cause of pain. Prolonged sitting or driving also elicits pain, although results of routine radiographic studies may be normal. Examination of the hip often reveals limitation of motion, particularly in internal rotation and passive flexion of the hip of more than 90�� while adducted. Passive flexion, adduction, and internal rotation also elicit some pain in patients with cam impingement [6]. The latter, which represents the impingement sign, is positive in all cases [7]. All other provocative maneuvers such as classic Trendelenberg test, Thomas test, anterior apprehension test, posterior impingement test, and the bicycle test are suggestive but nonspecific. A recent study by Kubiak-Langer et al [8] showed that the range of motion of the hips in patients with FAI is decreased in flexion, internal rotation, and abduction. Internal rotation is further decreased with increasing flexion and adduction. Most patients have a history of extensive diagnostic workups and perhaps even inappropriate surgical treatments such as repair of inguinal hernia, laparoscopy, and other abdominal procedures [9-11]. Imaging Studies Radiographic findings may be very subtle and missed easily. There may be a bony prominence in the anterolateral head-and-neck junction that is best seen on lateral view. The bony prominence is usually in the head-and-neck junction leading to reduced anterior offset of the femoral neck (Fig. 1A-B). Other abnormalities such as rim ossification (os acetabuli) and acetabular retroversion, as identified by the crossover sign of the anterior and posterior wall markings [12], may also be seen. A herniation pit may be found at the femoral neck, which is postulated as an indication of impingement. Most patients with impingement may require cross- sectional studies. Magnetic resonance imaging (MRI) has been used extensively to evaluate the pathology of the painful hip. Magnetic resonance imaging scan may miss the bony and articular pathology because of poor magnet strength of less than 1.5 T or failure to use surface coils over the hip. The reason for referral of many younger patients with hip pain is an MRI showing labral tear, although the x-ray findings are subtle or nondetectable. Magnetic resonance arthrogram also is per- formed, especially if no pathology was seen on MRI or if an articular defect is suspected. Labral separations from the anterior articular rim or tears were usually identified. Double densities (dye is seen between the articular cartilage and bone on magnetic resonance arteriogram) showed degen- erative defects of the articular cartilage or delamina- tion defects. Consequently, it is only recently, with sophisticated MRI techniques [13], that efforts at quantifying this deformity have been successful. 38 The Journal of Arthroplasty Vol. 22 No. 7 Suppl. 3 October 2007