Hip screw migration testing: First results for hip screws and helical blades utilizing a new oscillating test method

Abstract

Despite continued improvement in the methods and devices used to treat intertrochanteric fractures, there remains an unacceptable amount of failures. The cut-out rate for hip screws has been recorded up to 8.3%. To evaluate the migration of different implants under physiological loads, a multiplanar biomechanical test method for hip screws was developed, the first to incorporate a simulation of the human gait cycle by an oscillating flexion/extension movement of the test device. The new method was used to compare different hip screw and blade designs with respect to their directional migration resistance. The test method generated failure modes that were consistent with those observed clinically. Under cyclic loading, the hip screws migrated predominantly in a cephalad direction. In contrast, the helical blades exhibited a distinct migration in their axial direction. The Gamma3 hip screw design showed a significantly higher migration resistance compared with other screw and helical blade designs. The results demonstrate the ability of hip screws to significantly reduce axial migration and prevent cut-out under simulated walking loads. Further, the new multiplanar test method creates a physiological environment that can be used to optimize designs for intertrochanteric fracture fixation.