Steadman-Hawkins Clinic & Steadman-Hawkins Research Foundation, 181 W. Meadow Drive, Suite 1000, Vail, CO 81657, USA
Femoroacetabular impingement (FAI) has been recently revealed as a significant cause of hip pain in the athlete  and as a predictor of early onset hip osteoarthritis [2-4]. The hip is highly reliant on its bony structure for stability and support during substantial loading in weight bearing and sport. As a result, any abnormality in bony morphology may alter the force distribution in the joint, and can potentially cause injury to the capsulolabral structure or articular cartilage.
Ganz et al [5-7] have described two distinct types of FAI: cam and pincer. Cam impingement occurs when an abnormally shaped femoral head contacts a normal acetabulum, particularly during flexion and internal rotation. Pincer impingement involves a normal femoral head contacting an abnormally shaped, deep, or retroverted acetabulum. The patterns of labral and chondral injury resulting from the impingement appear to be unique to the distinct type of impingement . In cam impingement, the "bump" at the femoral head-neck junction produces a shearing force, displacing the labrum toward the capsule and the adjacent articular cartilage into the joint. Softening of the articular cartilage can be observed as a "wave sign" when arthroscopically probed before frank chondral delamination (Fig. 1). With repeated insults, the labrum may completely detach from the acetabular rim, and the cartilage may fully delaminate. In pincer impingement, the labrum is essentially trapped between the bony structures, thus it often bruises and flattens. With persistent pincer impingement, the labrum may degenerate, with cyst formation or ossification of the fibrocar-tilage. Persistent pincer impingement may lead to a chondral defect (a "contrecoup" lesion) at the posteroinferior acetabulum or posteromedial femoral head . The chondral injuries resulting from a pincer impingement are typically less severe than those resulting from a cam impingement.
Several mechanisms, particularly subtle developmental deformities, have been proposed for FAI. Subacute slipped capital femoral epiphysis has been shown to
* Corresponding author. E-mail address: [email protected] (M.J. Philippon).
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induce cam-type impingement, causing injury to the labium and adjacent articular cartilage [8-10]. Insufficient reduction of femoral neck fractures and decreased anteversion of the femoral neck have also been shown to cause cam impingement [11,12]. Pincer impingement may be caused by general acetabular overcoverage (coxa profunda) or acetabular retroversion [13,14], and has been shown to be associated with osteoarthritis of the hip . Demographically, cam impingement seems to be more common in young males and pincer impingement in female athletes.
In the athlete, FAI is a major cause of hip pain, reduced range of motion, and decreased performance. In fact, 36% (57 of 157) of professional and Olympic-level athletes who have undergone hip arthroscopic surgery between September 2000 and April 2005 have required decompression of FAI. Included in this group are professional hockey players, of whom 27 of 33 (81%) had FAI . No known studies have looked at possible mechanisms for overuse-type impingement in athletes. It is possible that each of these athletes with FAI suffers from a subtle developmental deformity due to a mild slip of the epiphysis during growth in adolescence. Subsequent damage to the labrum and articular cartilage could be worsened by their frequent sport activity. However, it is also possible that repetitive movement, particularly deep flexion, abduction, and internal rotation, may cause the abutment of the femoral neck with the ace-tabular rim. A reactive osteophyte may form at the head-neck junction, causing a cam-type impingement.
As described above, it has been shown that FAI can cause labral injury and early osteoarthritis. Therefore, surgery has proven necessary to increase joint clearance, particularly in flexion and internal rotation, in hopes of delaying the onset of osteoarthritis. Historically, only open osteoplasty for FAI decompression has been reported. Ganz and colleagues have supported this approach for its ability to provide an unobstructed 360° view of the femoral head and acetabulum [6,16]. It is our belief, however, that almost all areas of the head-neck junction and acetabular rim can be safely accessed through the arthroscope.
With the use of long and flexible arthroscopic instrumentation and controlled and precise intra-operative maneuvering of the lower extremity, we believe that arthroscopy can allow equivalent decompression of FAI when compared to the open technique. In addition, the arthroscopic approach seems to reduce postoperative morbidity, and provide a shorter rehabilitation time and quicker return to play for athletes.
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