Frequency and associated factor of atypical periprosthetic femoral fracture after hip arthroplasty

Background Atypical femoral fracture (AFF) is a serious complication after the use of bisphosphonates, and periprosthetic femoral fracture (PFF) appeared as a common complication after hip arthroplasty, especially in senile patients. Although American Society for Bone and Mineral Research has excluded PFFs from the definition of AFFs, several case reports found PFF patients undergoing bisphosphonate treatment, have fractures resembling AFF and the authors suggested that AFF can also occur in operated femurs after hip arthroplasty. To date, the frequency and risk factors of atypical PFF are unknown. The purpose of our study was (1) to evaluate the proportion of atypical PFF among Vancouver type B PFFs, and (2) to determine the association between occurrence of atypical PFF and use of bisphosphonate. Methods We reviewed medical records and radiographs of 67 Vancouver type B PFFs (67 patients) due to low-energy trauma and classified them into atypical PFF group and ordinary PFF group. We calculated the proportion of atypical PFFs among PFFs and identified risk factors for atypical PFF. Results Among the 67 PFFs, 7 fractures (10.4%) were classified as atypical PFF. Longer duration of bisphosphonate use was an independent risk factor of atypical PFF. (Odds ratio 2.600, 95% CI 1.184–5.709, p = 0.017). Conclusion In accordance with wide use of bisphosphonate, atypical PFFs after hip arthroplasty are not rare anymore. Physicians should suspect the atypical PFF, when they meet low-energy fracture in bisphosphonate users, and radiographs show features of AFF.