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    Original Research

    Prevalence of Radiographic Findings Thought to Be Associated with Femoroacetabular Impingement in a Population-based Cohort of 2081 Healthy Young Adults

    Published Online:Aug 1 2011https://doi.org/10.1148/radiol.11102354

    Abstract

    Overall, radiographic features suggestive of femoroacetabular impingement, both cam and pincer type, are quite common in a population of healthy young adults, especially in males, with a high degree of coexistence among most findings.

    Purpose

    To report the prevalence of qualitative radiographic findings for femoroacetabular impingement (FAI) and associations among them and to characterize the inter- and intraobserver variability of these interpretations.

    Materials and Methods

    This study is part of an institutional review board–approved population-based prospective follow-up of 2081 of 4006 (participation rate, 51.9%) young adults (874 [42.0%] male participants, 1207 [58.0%] female participants; mean age, 18.6 years) who took part in a randomized hip trial on developmental dysplasia of the hip. All participants gave informed consent. Two pelvic radiographs were obtained. Pistol-grip deformity, focal femoral neck prominence, and flattening of the lateral head, all suggestive of cam-type impingement, and the posterior wall sign, excessive acetabular coverage, and crossover sign, all suggestive of pincer-type impingement, were assessed subjectively by an experienced radiologist. To assess inter- and intraobserver agreement, images from 350 examinations were read independently twice by two observers.

    Results

    Cam-type deformities were seen in 868 male and 1192 female participants, respectively, as follows: pistol-grip deformity, 187 (21.5%) and 39 (3.3%); focal femoral neck prominence, 89 (10.3%) and 31 (2.6%); and flattening of the lateral femoral head, 125 (14.4%) and 74 (6.2%). Pincer-type deformities were seen in the same numbers of male and female participants, respectively, as follows: posterior wall sign, 203 (23.4%) and 131 (11.0%); and excessive acetabular coverage, 127 (14.6%) and 58 (4.9%) (all P < .001, according to sex distribution). The crossover sign was seen in 446 (51.4%) and 542 (45.5%) of the male and female participants, respectively (P = .004). There was a high degree of coexistence (odds ratio [OR] > 2) among most FAI findings. Interobserver agreement was good to very good (κ = 0.74–0.84) in rating cam- and pincer-type findings. Intraobserver agreement was moderate or good (κ = 0.49–0.80) for all findings for both observers.

    Conclusion

    Overall, radiographic FAI findings are quite common in a population of healthy young adults, especially in males, with a high degree of coexistence among most findings (OR > 2).

    © RSNA, 2011

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    Article History

    Received December 14, 2010; revision requested January 19, 2011; final revision received March 25; accepted April 4; final version accepted April 6.
    Published online: Aug 2011
    Published in print: Aug 2011