Reliability of measuring lateral bowing angle of the femur in patients with atypical femur fractures.

BACKGROUND: Lateral femoral bowing causes a higher tensile mechanical load on the lateral side of the femur, which plays a critical role in the pathogenesis of atypical femoral fractures (AFFs). There are many ways to measure lateral femoral bowing on plain radiographs, and there are difficulties in finding a correspondence point between measurements among multiple measurers. The purpose of this study is to prove the best method of correspondence between the investigators by analyzing the reliability of various methods for measuring lateral femoral bowing.

MATERIALS AND METHODS: We retrospectively collected data from 85 patients (87 femurs) diagnosed with AFF who had plain radiographs of entire femur from October 2013 to March 2018. The femoral bowing was measured in coronal view of femur plain radiographs using five methods (Sasaki, Morin, Jang, Kim, and Yau) by three examiners, respectively. The intra- and interobserver reliability of each method was assessed using intraclass correlation coefficient (ICC) for continuous variables.

RESULTS: All methods showed excellent intra- and interobserver reliability with ICC of >0.8. Among five methods, the Yau's method was the highest reliable method (ICC = 0.980, 95% confidence interval = 0.971-0.986).

CONCLUSIONS: All methods of measuring lateral femoral bowing in the coronal plane of plain radiographs are reliable. And, we recommend Yau's method, which has a clear reference point for measuring femoral bowing and is highest reproducible.