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

Objective: The purpose of this study was to evaluate the mechanical effects of using an injectable calcium phosphate cement, Norian Skeletal Replacement System (SRS), which is replaced by the native remodeling process, to augment sliding hip screw fixation of unstable intertrochanteric fractures in a cadaver model. Design: Ten matched pairs of human cadaver femora were used. One randomly selected femur from each pair was designated as experimental, whereas the contralateral femur served as the control. Setting: Testing was performed in the Orthopaedic Research Laboratories, The University of Michigan, Ann Arbor, Michigan, U.S.A. Patients/Participants: Femora with no radiographic evidence of pathology and with below-normal bone mineral density in the neck region were accepted into the study. Intervention: Three-part, intertrochanteric fractures were repaired by using a sliding hip screw and sideplate, without replacement of the posteromedial fragment. In the experimental side of each pair, SRS was used to grout the hip screw and to fill the posteromedial defect. Main Outcome Measurements: Femora were subjected to simulated single-leg stance loading to approximately one body weight in a servohydraulic testing machine. Measurements of stiffness, medial bone surface strain, hip screw displacement, and sideplate strain were made in Fractured femora. Stiffness and medial bone surface strain baseline data were obtained in the intact bone before fracture creation as well. Results: Augmenting fixation with Norian SRS increased the fracture construct stiffness and minimized sliding hip screw displacement. It also maintained medial bone surface strain closer to the intact state and lowered sideplate strain relative to controls. However, there was no difference in the load to failure between SRS-augmented and control femora. Conclusions: SRS augmentation of unstable, intertrochanteric fractures significantly improved overall stability, facilitated load transfer across the fracture, and decreased both shortening of the proximal femur and stress on the sliding hip screw.