Objective: Excessive curvature of the femur has been considered to be one of the factors associated with atypical femoral fracture (AFF). Although we clarified that femoral curvature was markedly influenced by a low vitamin D level, very few studies have been conducted on the direct relationship between AFF and a serum low level of vitamin D. Therefore, we compared the serum vitamin D level between AFF and osteoporosis patients. Methods: A total of 48 consecutive AFFs in 36 Japanese patients were retrospectively reviewed using the medical records, and 12 consecutive AFFs in 9 patients (AFF group) whose 25-hydroxyvitamin D (25(OH)D) levels were examined were included in this study. As a non-AFF control group, 45 consecutive age-matched female patients with osteoporosis (Osteoporosis group) were enrolled. We compared some laboratory examination items, the bone mineral density, and curvature of the femur. Results: When univariate logistic regression analysis was performed to compare the 2 groups, Ca levels and lateral and anterior curvatures in the AFF group were significantly greater than in the Osteoporosis group (P < 0.05, P < 0.01, and P < 0.01, respectively), and the 25(OH)D level in the AFF group was significantly lower than in the Osteoporosis group (P < 0.01). We used discriminant analysis of these extracted items to exclude the mutual influence of factors and identify factors closely associated with AFF, and 25(OH)D, Ca and anterior curvature were identified as significant items to differentiate these diseases (P < 0.05, P < 0.01, and P < 0.01, respectively). Conclusion: AFF patients showed low vitamin D levels and marked femoral curvatures.
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