Critical differences between subtrochanteric and diaphyseal atypical femoral fractures: analyses of 51 cases at a single institution in Korean population

Summary: There still remains controversy on the pathomechanism of atypical femoral fracture (AFF). The angle of lateral bowing and bone mineral density showed significant differences between subtrochanteric and diaphyseal atypical fracture groups. In addition to the use of bisphosphonate, mechanical factors might play important roles in the occurrence of AFFs. Introduction: Although AFF could be divided into subtrochanteric and diaphyseal fracture according to the location of fractures, there is a lack of evidence regarding differences between two fractures and etiology of the occurrence. The aim of study is to determine differences between atypical subtrochanteric and diaphyseal fracture in Korean population. Methods: Between February 2010 and March 2015, 51 AFFs in 40 patients were included in this study. Their medical records were retrospectively reviewed. The AFF patients satisfied all the diagnostic criteria of the 2014 revised edition of the ASMBR. To analyze the differences according to the location of fracture, the AFFs were divided into subtrochanteric (n = 16) and diaphyseal (n = 35) fracture groups. The following factors were compared between two groups: patients’ demographics, underlying diseases, laboratory findings (serum-25(OH) VitD3, osteocalcin, c-telopeptide, ALP, Ca, and P), bone mineral density (BMD), duration of bisphosphonate (BP) usage, and lateral bowing of the femur at time of the fracture. Results: All AFFs happened in female patients (mean age, 73.8 years) who have received bisphosphonate treatments except three patients. The mean duration of bisphosphonate usage was 95.3 months. Between the two groups, demographic data (age, height, weight, and BMI), underlying diseases, laboratory findings, hip BMD, and duration of BP treatment were comparable to each other (p > 0.05). However, the subtrochanteric fracture group showed higher FNSBA (femoral neck shaft bowing angle, p < 0.001) and spine BMD (p = 0.014) compared to the diaphyseal fracture group. Conclusions: Angle of lateral bowing (FNSBA) and spine BMD showed significant differences between subtrochanteric and diaphyseal atypical fracture groups. According to our results, femoral bowing and spine BMD may play important roles in the AFF locations.