Biomechanical evaluation of calcium phosphate cement-augmented fixation ofunstable intertrochanteric fractures

Objective: The purpose of this study was to evaluate the mechanical effects of using an injectable calcium phosphate cement, Norian Skeletal Replaceme nt System (SRS), which is replaced by the native remodeling process, to aug ment sliding hip screw fixation of unstable intertrochanteric fractures in a cadaver model. Design: Ten matched pairs of human cadaver femora were used. One randomly s elected femur from each pair was designated as experimental, whereas the co ntralateral femur served as the control. Setting: Testing was performed in the Orthopaedic Research Laboratories, Th e University of Michigan, Ann Arbor, Michigan, U.S.A. Patients/Participants: Femora with no radiographic evidence of pathology an d with below-normal bone mineral density in the neck region were accepted i nto the study. Intervention: Three-part, intertrochanteric fractures were repaired by usin g a sliding hip screw and sideplate, without replacement of the posteromedi al fragment. In the experimental side of each pair, SRS was used to grout t he hip screw and to fill the posteromedial defect. Main Outcome Measurements: Femora were subjected to simulated single-leg st ance loading to approximately one body weight in a servohydraulic testing m achine. Measurements of stiffness, medial bone surface strain, hip screw di splacement, and sideplate strain were made in Fractured femora. Stiffness a nd medial bone surface strain baseline data were obtained in the intact bon e before fracture creation as well. Results: Augmenting fixation with Norian SRS increased the fracture constru ct stiffness and minimized sliding hip screw displacement. It also maintain ed medial bone surface strain closer to the intact state and lowered sidepl ate strain relative to controls. However, there was no difference in the lo ad to failure between SRS-augmented and control femora. Conclusions: SRS augmentation of unstable, intertrochanteric fractures sign ificantly improved overall stability, facilitated load transfer across the fracture, and decreased both shortening of the proximal femur and stress on the sliding hip screw.