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

Implant type does not significantly alter torsional bone strength in rabbit femora after screw or wire insertion.

This experimental biomechanical study evaluated implant-induced bone loss and torsional mechanical properties following insertion of three common orthopaedic implants—cortical screws, locking screws, and Kirschner wires—in rabbit (Oryctolagus cuniculus) femora. Eighteen femora from skeletally mature New Zealand White rabbits were randomly assigned to receive bicortical defects created by one of the three implant types (n=6 per group). After implant insertion and removal, specimens underwent micro-computed tomography (micro-CT) to quantify normalized peri-implant bone volume loss, followed by torsional mechanical testing to failure. Qualitative assessment revealed larger bone chips at insertion sites for both screw types compared with Kirschner wires. Micro-CT analysis showed 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). Despite this difference in volumetric bone loss, biomechanical testing revealed no significant differences among groups in torsional rigidity, yield torque, ultimate rotation, or ultimate torque. These findings suggest that while self-tapping cortical screws cause greater volumetric bone loss than locking screws in rabbit femora, this additional damage does not translate into measurable differences in torsional mechanical properties. The authors conclude that implant insertion alone is unlikely to be the primary contributor to catastrophic fracture repair failures observed in rabbits, directing attention toward other mechanical or biological factors in post-operative complications.

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