Optimal placement of the temporary fixation pin in tibial plateau leveling osteotomy: a canine ex vivo study

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 within the tibial tuberosity, but the biomechanical impact of temporary fixation pin positioning relative to these fibers has not been experimentally quantified.

Eighteen pelvic limbs from nine small-breed canine cadavers (mean body weight 5.98 kg) were randomized to three groups (n = 6) based on temporary fixation 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 specimens underwent a 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) confirmed comparable anatomy across groups. Group 1 exhibited significantly higher maximum failure loads compared to Groups 2 and 3 (p < 0.017), with no significant difference between those two groups. 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 through pin tract at the mid-crest.

Positioning the temporary fixation pin at the level of the SF markedly enhances the biomechanical resistance of the tibial tuberosity under tensile loading in ex vivo TPLO models. These findings endorse precise proximal pin placement as a modifiable surgical parameter to mitigate fracture risk in small-breed dogs. Future investigations employing dynamic loading protocols and evaluating breed-specific anatomical variations are warranted to validate these results in vivo.