Evaluation of the nature and etiologies of risk factors for diaphyseal atypical femoral fractures.

OBJECTIVES Differences in the mechanisms of subtrochanteric and diaphyseal atypical femoral fractures (AFFs) have been speculated in studies that have analyzed differences in the patients' backgrounds. However, the etiologies of each type of AFF have not been investigated in detail. Therefore, this study aimed to investigate the nature and etiologies of the risk factors for diaphyseal AFFs. MATERIALS AND METHODS Eighty consecutive Japanese patients with 91 diaphyseal AFFs (the AFF group) and 110 age-matched female patients with osteoporosis (the non-AFF control group) were included. Their clinical data were compared and the factors affecting AFFs were investigated. Furthermore, the etiologies of the risk factors for diaphyseal AFFs were examined. RESULTS Multivariate analysis revealed that femoral serrated changes, bisphosphonate or denosumab usage, and lateral and anterior femoral curvatures were the risk factors for diaphyseal AFFs (p<0.0011, p=0.0137, and p<0.0001, respectively). Multivariate analyses also revealed that serrated changes and low serum 25(OH)D levels affected the lateral curvature (p=0.0088 and 0.0205, respectively), while serrated changes affected the anterior curvature (p=0.0006); each significantly affected the femoral curvature. In addition, a high serum calcium (Ca) level, lateral femoral curvature, and anterior femoral curvature were the predictors of serrated changes (p=0.0146, 0.0002, and 0.0098, respectively). CONCLUSION The risk factors for diaphyseal AFFs were bone resorption inhibitor usage, a strong femoral curvature, and serrated changes. A low serum 25(OH)D level and serrated changes are the risk factors for lateral curvature, while a high serum Ca level is a risk factor for serrated changes.