Study of Atypical Femoral Fracture Cases Coupled in a Multicenter Study.

UNLABELLED: There are several causes of atypical femoral fractures (AFF) in elderly Japanese patients, including longterm bisphosphonate (BP) use or bowed femoral shaft stress fractures, but the available sample size for examining AFF etiology in a single institution is limited. The purpose of this study was to categorize the characteristics of AFF by analyzing the data compiled on patients treated at our hospital and at affiliated institutes. This multicenter, retrospective, observational study included 34 AFF cases (bilateral AFF 10) in one male and 23 female patients (age range 30-90 years, mean age 73.0 years). Evaluation measures included the presence/absence of BP use, duration of BP use, history of other drug use, presence/absence of comorbidities, fracture site, presence/absence of femoral lateral bowing, bone biopsy parameters, and time to bone union. Nineteen patients were prescribed BP for osteoporosis (duration range 4-10 years, mean duration 6.1 years). Subtrochanteric and femoral shaft fractures were seen in 16 and 18 cases, respectively (complete fractures 22, incomplete fractures 12). Femoral lateral bowing (n = 16) occurred with femoral shaft fractures. Mean time to bone union was 9.0 months (complete fractures 11.3 months, incomplete fractures 3.7 months). AFF could be substantially caused by three factors: BP use, drugs other than BP/comorbidity, and femoral lateral bowing. Twenty four patients were classified as having BP-related-type (n = 2), drug/comorbidity-type (n = 3), lateral bowing-type (n = 2), or mixed-type (n = 17) AFF. AFF etiology cannot be explained by a single cause; thus, a multifactorial etiology, including poor bone quality due to mutual interactions and mechanical stress, seems to be responsible for the occurrence of AFF. LEVEL OF EVIDENCE: Ⅳ diagnostic.