Influence of fragment volume on stability of 3-part intertrochanteric fracture of the femur: a biomechanical study.

Complex unstable fracture can complicate the treatment outcome of intertrochanteric fracture of the femur, and fixation failure after surgery is a significant problem in elderly patients. This study aimed to evaluate the effect of fracture geometry on the stability of 3-part intertrochanteric fracture by assessing the fragment size. Four categories (group I: large greater trochanter, small lesser trochanter; group II: large greater trochanter, large lesser trochanter; group III: small greater trochanter, small lesser trochanter; and group IV: small greater trochanter, large lesser trochanter) of a 3-part intertrochanteric fracture model were designed. Three-dimensional computer tomography scanning was performed to measure the volume of each fragment. After fixation with a dynamic hip screw, a cyclic loading study was conducted using a servohydraulic machine. There was a significant difference in fatigue failure between each group. After all specimens had endured 10,000 cycles with a range of loads (100-1,000 N), the mean number of cycles until fixation failure with a load range of 200-2,000 N was 1,467.67 ± 199.92 in group I; 579 ± 93.48, group II; 398.17 ± 37.92, group III; and 268.67 ± 19.92, group IV. Fixation strength was approximately 5 times greater in group I than in group IV. In 3-part intertrochanteric fracture, the sizes of the greater and lesser trochanteric fragments are important factors for determining stability after dynamic compression screw fixation. This study supports our hypothesis that the volumetric ratio of ∆lesser trochanter/∆greater trochanter can be used to predict stability of intertrochanteric femoral fracture.