Predicting the Mechanical Outcome of Femoral Neck Fractures Fixed with Cancellous Screws: an in Vivo Study

Objective: The goal of this project was to determine, by using a retrospective cohort analysis, the relative importance of fracture geometry, bone density, and quality of fracture reduction in predicting redisplacement of femoral neck fractures fixed with multiple cancellous screws in a patient population.

Design: A retrospective analysis of quantitative geometric and bone density data from forty-seven patients with femoral neck fractures fixed with cancellous screws was performed.

Setting: Radiographs retrieved after analysis of a statewide hospital database were digitized and analyzed quantitatively.

Intervention: Quantitative data from radiographs included estimates of femoral neck bone density, fracture surface orientation and location, degree of comminution, prefixation displacement, initial reduction position of the fractured component, and final displacement of the fracture after fixation.

Main Outcome Measurements: Angular rotation and inferior displacement of the fracture component after fixation.

Results: Femoral neck bone density can be correlated to femoral cortical thickness and can be used as a measure of bone density from plain x-rays. Significant relative risk of redisplacement of a femoral neck fracture is correlated with initial inferior offset of the fracture component and varus angulation. Relative risks of other variables, including valgus reduction, Garden Stage 3 and 4 position of the femoral head, low bone density, presence of inferior comminution, a more vertical fracture surface angle, and fracture position, were not significant.

Conclusions: When compared with other geometric and mechanical variables, nonanatomic reduction of a femoral neck fracture, with either inferior offset or varus angulation, is the strongest predictor of postfixation redisplacement of the fracture.