The Correlation Between Lateral Bowing Angle of the Femur and the Location of Atypical Femur Fractures

This study is the first to report the use of data on incomplete atypical femur fracture (AFF) to evaluate the curvature of femur and explore the relationship between lateral femoral bowing angle (FBA) and AAF location. In this study, we obtained 17 cases of incomplete AFF and calculated the accurate lateral FBA and location ratio of the incomplete fracture. Incomplete fracture location was defined as a percentage (length from lesion to greater trochanter tip/entire femur length %; greater trochanter tip: 0 %; femoral condyles: 100 %). A lateral FBA of 7° was set as the point of demarcation. Eleven femurs had a lateral FBA ≤ 7° (group 1), with a median lateral FBA of 4.75° (IQR 2.5–5.9°) and a median of incomplete AFF location at 25.2 % (IQR 23.4–30.1 %). Another six femurs had a FBA > 7° (group 2) with a median of 1.8° (IQR 10.2–14.3°) and a median location at 47.7 % (IQR 38.6–54.5 %). There was a significant statistical difference in location (p < 0.05) between the two groups. The rate of BP use was 87.5 % in group 1 which was higher than 60 % in group 2. There was some degree of positive correlation between the bowing angle and location in simple linear regression (r ² = 0.549, p < 0.001, ß = 1.789). AAFs located in diaphysis were associated with large lateral FBA. On the other hand, AAFs located in subtrochanteric region were more commonly found in femurs with smaller lateral FBA. In conclusion, the degree of the FBA was associated with AFF location.