Alpha angle correction in femoroacetabular impingement
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PURPOSE: The predictive value of the alpha angle, currently the most validated magnetic resonance imaging parameter for CAM-impingement FAI, remains to be systematically evaluated in the orthopaedic literature. A systematic review was conducted to determine whether alpha angle correction influences clinical outcomes in patients with FAI. METHODS: We searched three databases (MEDLINE, EMBASE and PubMed) for English clinical studies published up to August 2012, reporting surgical correction of the alpha angle in patients with a primary diagnosis of FAI. Two independent assessors reviewed eligible studies. Where applicable, the Newcastle-Ottawa Scale was used to perform a quality assessment. Descriptive statistics are presented. RESULTS: Of the 1,103 studies initially retrieved, 14 fulfilled our eligibility criteria. Majority of studies (86 %) were case-control designs, with no randomized controlled trials. Variability existed in the surgical techniques and modalities used to measure pre- and post-operative alpha angles. All 14 studies reported a mean measured post-operative restoration of a normal alpha angle (equal to or less than 55°). Failure due to inadequate osseous correction was cited in 3/14 included studies. Correction resulted in significant improvements in range of motion and patient Visual Analog Scales, non-arthritic hip scores, Harris Hip Scores and the short-form-12. CONCLUSION: Based on this review, there is evidence supporting that precise surgical restoration of the alpha angle in CAM-type FAI to a minimum of less than 55° will lead to improved patient outcomes. The alpha angle is a good predictor of outcome and represents a simple, reproducible and inexpensive guide that can be used intra-operatively and post-operatively.
