Optimal Placement of Temporary Anti-rotation Pin in Tibial Plateau Leveling Osteotomy: A Canine Ex Vivo Study

Background Tibial Plateau Leveling Osteotomy (TPLO) is widely accepted for stabilizing the stifle joint in dogs with cranial cruciate ligament disease. However, postoperative tibial tuberosity fractures remain a significant complication, particularly in small-breed dogs. Recent anatomical findings suggest that Sharpey’s fibers(SF) contribute to local structural reinforcement, yet the biomechanical implications of anti-rotation pin positioning relative to these fibers have not been experimentally quantified. Results Eighteen pelvic limbs from nine small-breed canine cadavers (mean body weight 5.98 kg) were assigned to three groups (n = 6) based on anti-rotation pin positioning. Group 1 had the pin inserted perpendicular to the tibial mechanical axis at the level of SF. Group 2 received pin placement 3 mm distal, and Group 3 received placement 6 mm distal and inclined from cranial to caudal. All limbs underwent standardized TPLO, followed by mounting at a standing angle of 135°, and vertical tensile force was applied until failure. Pre- and postoperative tibial plateau angle (TPA) and absolute tibial tuberosity width (ATTW) were measured to ensure anatomical consistency. Group 1 exhibited significantly higher maximum failure loads compared to Groups 2 and 3 (p < 0.017), with no significant difference between the latter two. Fracture configuration differed notably: Group 1 showed complex, comminuted fractures of the distal tibial crest, while Groups 2 and 3 demonstrated simple linear transverse fractures at the mid-crest region. Conclusions Placement of the anti-rotation pin at the level of SF significantly enhances biomechanical resistance of the tibial tuberosity under tensile loading following TPLO. These findings support precise vertical pin positioning as a modifiable surgical variable to reduce fracture risk in small-breed dogs. Further in vivo studies incorporating dynamic loading and breed-specific anatomical variation are warranted to confirm these ex vivo results.