Torsional Strength Reduction of Rabbit (Oryctolagus cuniculi) Femora is Not Significantly Different after Insertion of Cortical Screws, Locking Screws or Kirschner Wires.

OBJECTIVE: This study aims to quantify implant-induced bone loss and changes in torsional mechanical properties following insertion of three common orthopaedic implants - cortical screws, locking screws and Kirschner wires in rabbit femora. STUDY DESIGN: Eighteen femora from skeletally mature New Zealand White rabbits were used. Femora were randomly assigned to receive a bicortical defect created using a self-tapping cortical screw, self-tapping locking screw or smooth Kirschner wire (n = 6 per group). Following implant insertion and removal, specimens underwent micro-computed tomography to quantify normalized peri-implant bone volume loss, followed by torsional mechanical testing to failure. RESULTS: Qualitative assessment revealed larger bone chips at the insertion site for both screw types compared with Kirschner wires. Micro-computed tomography analysis demonstrated significantly greater total bone volume loss following cortical screw insertion (11.7 ± 3.4%) compared with locking screws (8.6 ± 1.4%; p = 0.0459). No differences were observed between groups in torsional rigidity, yield torque, ultimate rotation and ultimate torque during biomechanical testing. CONCLUSION: These findings indicate that, although self-tapping cortical screws induce greater volumetric bone loss than locking screws in rabbit femora, this damage does not translate into significant differences in torsional rigidity, yield torque, ultimate rotation or ultimate torque among the tested implants. Implant insertion alone is therefore unlikely to be the primary contributor to catastrophic failure seen with specific fracture repair techniques in the rabbit.