Anterolateral femoral bowing and loss of thigh muscle are associated with occurrence of atypical femoral fracture: Effect of failed tension band mechanism in mid-thigh.

Background: The purpose of this study was to characterize anterolateral bowing of the femur using X-rays and muscular atrophy in the mid-thigh using computed tomography (CT) in patients with atypical femoral fractures (AFFs). We then compared the results with those of an intertrochanteric fracture to understand whether these measures act as causative factors of AFFs.
Methods: From January 2009 to December 2015, 37 patients with complete AFF and 12 patients with incomplete AFF were enrolled in this study. Lateral femoral bowing, anterior femoral bowing, cross-sectional area (CSA), and attenuation coefficient of thigh muscles in the AFF group are measured and compare with those in the intertrochanteric fracture group.
Results: Lateral and anterior femoral bowing in the AFF group were significantly higher than those in the intertrochanteric fracture group. The level of fracture was found to be significantly associated with lateral and anterior femoral bowing (r = 0.569, r ²  = 0.324, p < 0.001; r = -0.530, r ²  = 0.281, p < 0.001, respectively). Total CSA and CSA of anterior and medial compartments were significantly lower in the AFF group (p < 0.05). The attenuation coefficient of the total thigh muscle and all three compartments in the AFF group were significantly lower than those in the intertrochanteric fracture group (p < 0.05).
Conclusions: This study demonstrated that anterolateral femoral bowing and loss of thigh muscle were highly associated with the occurrence of AFFs.
(Copyright © 2016 The Japanese Orthopaedic Association. Published by Elsevier B.V. All rights reserved.)