Prevalence of pincer, cam, and combined deformities in Japanese hip joints evaluated with the Japanese Hip Society diagnostic guideline for femoroacetabular impingement: A CT-based study

Background: Femoroacetabular impingement (FAI) is thought to be associated with hip osteoarthritis. We investigated the prevalences of radiologic deformities of the pincer, cam, and their combinations in Japanese hip joints using computed tomography (CT) according to the Japanese Hip Society diagnostic guideline for FM. Methods: Multi-slice CT images were evaluated. Pincer deformities were defined as: type 1: center-edge angle (CE) >= 40 degrees; type 2: CE >= 30 degrees and acetabular roof obliquity <= 0 degrees; type 3: CE >=degrees 25 and retroverted acetabulum. Cam deformities were defined as: type 1: CE >= 25 degrees, alpha-angle >= 55 degrees, and head neck offset ratio <0.14; type 2: CE >= 25 degrees, alpha-angle >=degrees 55, and herniation pit positive; type 3: CE >= 25 degrees, alpha-angle >55 degrees, and pistol grip deformity positive. Results: We studied 128 hips. Pincer was detected in 35.9% (type 1, 12.5%; type 2, 18.0%; type 3, 13.3%). Cam was detected in 24.2% (type 1, 23.4%; type 2, 7.8%; type 3, 10.9%). Combined deformities were detected in 10.2%. Type 3 pincer/type 1 cam was the most frequent combined deformity compared with all combined deformities. All of the cam deformities, total combined deformities, and all radiological FAIs appeared significantly more often in men. Conclusions: When we used this guideline to diagnose FAI in a Japanese population, radiological FAI was common, and pincer deformities were more common than cam deformities. The most frequent seen pincer, cam, and combined deformities was type 2 pincer, type 1 cam, and the combination of type 3 pincer/type 1 cam, respectively. (C) 2016 The Japanese Orthopaedic Association. Published by Elsevier B.V. All rights reserved.