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

OBJECTIVES: To compare the strength of augmented versus nonaugmented fixation techniques for stabilizing vertical shear femoral neck fractures.

METHODS: 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.

RESULTS: 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%.

CONCLUSIONS: 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.