Biomechanical analysis of augmented plate fixation for the treatment of vertical shear femoral neck fractures.

Abstract

To compare the strength of augmented versus nonaugmented fixation techniques for stabilizing vertical shear femoral neck fractures. Two surgical screw constructs were tested with and without augmentation using 40 composite femurs: (1) 7.3-mm cannulated screws placed in an inverted triangular configuration and (2) 135-degree dynamic hip screw (DHS). The augmentation consisted of a 2.7-mm locking plate placed on the anterior-inferior femoral neck. Specimens in all 4 groups were tested with load to failure, while failure loads, energy absorbed to failure, and axial stiffness were determined. These data were then analyzed using a two-way (construct × augmentation) analysis of variance. There was no statistically significant interaction between screw construct and augmentation for load to failure (P = 0.11). Augmentation with the 2.7-mm locking plate increased failure loads in both constructs on average by 83% (2409 vs. 4417 N, P < 0.01). Femurs instrumented with cannulated screws had 26% higher loads to failure than those instrumented with DHS (3879 vs. 3087 N, P < 0.01). On average, the augmentation increased energy absorbed to failure by 183% and constructs' stiffness by 35%. The strength of surgical repairs of the vertical shear femoral neck fractures can be significantly augmented with the 2.7-mm locking plate. The construct with the cannulated screws was significantly stronger than the DHS construct.