Assessment of the α-angle of femoral neck and morphological classification of the anterior femoral head-neck junction on CT-based images in normal Chinese adults

Abstract

Objective To investigate the normal range of the femoral neck α-angle in normal Chinese adults and classify the morphology of the anterior femoral head-neck junction on CT-based images. Methods Six hundred and fifty-two adult patients (Bilateral: 459 patients, unilateral:193 patients) with the total of 1111 hips (552 left; 559 right, and 654 male; 457 female) without known diseases affecting the proximal femur or symptoms of femoroacetabular impingement (FAI) underwent 64-slice CT scanning for medical purpose with the hip included in the scan range. The volume CT data was used for further analysis in this study. Oblique sagittal plane images paralleling to the axis of the femoral neck were reconstructed with the volume CT data, the image through the middle of the femoral neck was chosen to measure α-angle with AutoCAD2006 software. The morphology of the anterior femoral head-neck junction was classified. Analysis of variance and t-test were performed with SPSS 15.0. Results The mean value of α-angle of all 1111 hips was 38. 2° ±5.3°. The normal range of α-angle in Chinese adults was 28°to 49°.The mean value of left and right α-angles were 38. 0° ±5. 3°and 38.4° ±5. 3° ,respectively, and there was no statistically significant difference between both sides (t = - 1. 231 ,P ＞ 0. 05 ). Males have greater α-angles than females 39. 2° ±5. 8 vs 36. 8° ±4. 1°, with t = -8. 180, P ＜0. 01. There was no statistically significant differences of the α-angles of the seven age groups (F = 1. 765, P ＞ 0. 05 ). In all 1111 proximal femora, 168 were classified as concave type, accounting for 15. 1%, with a mean α-angle of 31.2° ±2. 0°,726 were smooth type, accounting for 65.4%, with a mean α-angle of 37.4° ± 2. 4°, and 217 were flat type, accounting for 19.5%, with a mean α-angle of 46. 4° ±3. 8°. The differences of the α-angles of the three groups reached statistical significance ( F = 1636. 107, P ＜ 0. 01 ). Conclusions The morphology of anterior femoral head-neck junction can be classified into three types: concave type (type Ⅰ ), smooth type (type Ⅱ ) and flat type (type Ⅲ ). This classification could directly reflect α-angle, which helps to recognize the variation of the offset of anterior femoral head-neck junction. This study offers basic data for the diagnosis of FAI. Key words: Femur neck; Femur head; Tomography, X-ray computed; Anthropometry