Clinical and femoral radiological characteristics of South-East Asian osteoporosis patients with atypical femoral fractures: Case control study with matching of bisphosphonate exposure.

Abstract

Atypical femoral fractures (AFF) are stress fractures in the femur that may occur with prolonged exposure to anti-resorptive treatments. Asians have a disproportionately higher risk factor for AFF at 5-6 times that of Caucasian and Hispanic patients. It has been hypothesized that the Asian femora geometry may be a contributing factor in the pathogenesis of AFF. We conducted a case-control study with matching of bisphosphonate exposure to assess the role of femoral geometry and imaging in association with clinical risk factors in South-East Asian patients with AFF. This is a single-site case-control study of clinical risk factors and femoral radiological characteristics in AFF patients, matched on bisphosphonate (BP) exposure. Subjects were recruited from Changi General Hospital fracture database as well as orthopaedic wards and endocrine clinics. They were matched by age, gender, and BP exposure duration. We analysed demographic, clinical, and biochemical variables. The 46 AFF cases and 46 controls recruited were well matched in clinical and demographic characteristics, as well as in the duration of exposure to BP (78.7 months in AFF cases and 70.7 months in controls). There were larger femoral offsets in AFF patients compared to controls (41.9 mm vs 36.3 mm, p = 0.0409). A subgroup analysis showed that lateral femoral bowing angles were more varus in shaft AFFs vs subtrochanteric AFFs (-6.53° vs -2.81°, p = 0.013), while the site of maximal femoral cortical thickness was situated more distally in shaft compared to subtrochanteric AFFs (0.432 vs 0.385, p = 0.023). Baseline and follow-up hip BMD for AFF cases were significantly higher in the total hip and femoral neck region compared to controls, there were similar rates of BMD improvements in both groups. In this study of clinical and femoral radiological characteristics of South-East Asian AFF cases and matched controls, there were significantly larger femoral offsets and higher BMD scores in the hip of AFF cases versus controls. Further studies are needed to better understand the role of femoral radiological and BMD characteristics in the development of AFF in individuals exposed to bisphosphonates.