Inclusion and Exclusion Criteria in the Diagnosis of Femoroacetabular Impingement.

PURPOSE: The purpose of this study was to clarify the criteria for femoroacetabular impingement (FAI) by way of a systematic review of FAI-related articles, as well as to define more appropriate inclusion or exclusion criteria in the diagnosis of FAI. METHODS: A systematic review of FAI-related articles was performed using Web of Science. Thirty-two articles met the inclusion and exclusion criteria. In these articles we investigated radiographic findings for the diagnosis of FAI and the prevalence of each FAI-related finding. RESULTS: The crossover sign was used in 22 articles (69%); acetabular index, 9 articles (28%); posterior wall sign, 7 articles (22%); and prominence of the ischial spine sign, 3 articles (7%). Regarding acetabular coverage, the lateral center-edge (LCE) angle was described in 13 articles (41%), in which an LCE angle either of more than 40° or of more than 30° combined with an acetabular index of less than 0° was considered an inclusion criterion for pincer impingement. Meanwhile, the alpha angle was used in 28 articles (88%), in which 50° or 55° was recommended as a positive finding of cam impingement. CONCLUSIONS: Common findings of pincer or cam deformity were used to select FAI patients with sufficient coverage of the acetabulum with an LCE angle of more than 25°. Patients with an LCE angle of less than 25° or those with local acetabular deficiency regardless of having a normal LCE angle should be excluded from the FAI criteria, even if the FAI-related findings are positive. LEVEL OF EVIDENCE: Level IV, systematic review of Level I through IV studies.