Evaluation of the Alpha Angle in Asymptomatic Adult Hip Joints: Analysis of 994 Hips

Abstract

Numerous studies on cam femoroacetabular impingement (FAI) causing osteoarthritis have been conducted in Western populations, but not in Asian populations. The alpha angle in cam type FAI can be measured by routine hip AP and axial radiographs. The purpose of this study was to determine the range of alpha angles in an asymptomatic Asian cohort. We performed a retrospective examination on 500 asymptomatic Asian adults (1000 hips) who underwent simultaneous spine MRI and hip coronal survey MRI for evaluation of back pain from December 2009 to March 2010. The alpha angle was measured on anteroposterior (AP) pelvic survey images. According to inclusion criteria, 372 hips of 186 men and 622 hips of 311 women were analysed. The mean alpha angles for men and women were 50.61° ± 7.61° and 49.82° ± 4.14°, respectively with no statistically significant differences (p = 0.063). Alpha angles of the two age groups (≥50 years old and <50 years old) were similar in both genders: 49.90° ± 6.88° versus 51.40° ± 8.30° in men (p = 0.060), and 50.61° ± 7.61° versus 49.82° ± 4.14° in women (p = 0.71). The frequency of pathologic alpha angle of men and women was 0.5% and 3.1%, respectively. After review of 994 asymptomatic adult hips, we found neither gender-specific nor age-specific differences in the alpha angle. The frequency of the pathological range of the alpha angle was notably rare, as compared to those of Western countries. We assume that these findings could be related to a low prevalence of FAI and idiopathic osteoarthritis of the hip in the Asian population.