title: The plain beta-angle measured on radiographs in the assessment of femoroacetabular impingement.
abstract: The beta-angle is a radiological tool for measuring the distance between the pathological head-neck junction and the acetabular rim with the hip in 90 degrees of flexion in patients with femoroacetabular impingement. Initially it was measured using an open-chamber MRI. We have developed a technique to measure this angle on plain radiographs. Correlation analysis was undertaken to determine the relationship between the range of movement and the beta-angle in 50 patients with femoroacetabular impingement and 50 asymptomatic control subjects. Inter- and intra-observer reliability of the beta-angle was also evaluated. Patients with femoroacetabular impingement had a significantly smaller (p < 0.001) mean beta-angle (15.6 degrees, 95% confidence interval (CI) 13.3 to 17.7) compared with the asymptomatic group (38.7 degrees, 95% CI 36.5 to 41.0). Correlation between internal rotation and the beta-angle was high in the impingement group and moderate in the asymptomatic group. The beta-angle had excellent inter- and intra-observer reliability in both groups. Our findings suggest that the measurement of the beta-angle on plain radiography may represent a valid, reproducible and cost-effective alternative to open MRI in the assessment of the pathological bony anatomy in patients with cam, pincer and mixed femoroacetabular impingement.
authors.affiliation: Department of Orthopaedic Surgery, The Cantonal Hospitals Lucerne, Eichenweg, 6010 Wolhusen, Switzerland. a-r.brunner@web.de
authors.forename: A
authors.initials: A
authors.lastname: Brunner
authors.forename: A T
authors.initials: AT
authors.lastname: Hamers
authors.forename: M
authors.initials: M
authors.lastname: Fitze
authors.forename: R F
authors.initials: RF
authors.lastname: Herzog
mesh_terms: D000077:Acetabulum / Q000000981:diagnostic imaging*; D000293:Adolescent; D000328:Adult; D005260:Female; D005270:Femur Head / Q000000981:diagnostic imaging*; D006621:Hip Joint / Q000002:abnormalities* / Q000473:pathology*; D006801:Humans; D007592:Joint Diseases / Q000000981:diagnostic imaging; D007593:Joint Instability / Q000000981:diagnostic imaging*; D008297:Male; D008875:Middle Aged; D015588:Observer Variation; D011859:Radiography; D016059:Range of Motion, Articular; D015203:Reproducibility of Results; D055815:Young Adult