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

Abstract

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

Results: 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.

Conclusions: 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.

Keywords: Sharpey’s fibers; Small breed dogs; Temporary fixation pin; Tensile test; Tibial plateau leveling osteotomy; Tibial tuberosity fracture.

Fig. 1

Schematic illustrations of the temporary fixation pin placement in three groups. A Group 1: pin placed adjacent to the SF; B Group 2: pin placed 3 mm distal to the SF; C Group 3: pin placed 6 mm distal with an inclined cranial-to-caudal trajectory

Fig. 2

Immediate postoperative mediolateral radiographs of the stifle following TPLO and temporary fixation pin placement. Radiographs represent (A) Group 1, (B) Group 2, and (C) Group 3. White arrows indicate the insertion site of the removed temporary fixation pin. Radiographic measurements of ATTW, TPA, and rotation distance were performed to confirm eligibility for biomechanical testing

Fig. 3

A photograph of the axial tensile testing model. Each specimen was secured at 135° relative to the tibial axis and subjected to vertical distraction (indicated by the arrow) at a constant rate of 10 mm/min until tibial tuberosity failure occurred

Fig. 4

Maximum failure loads under axial tensile force among groups. Different superscript letters indicate significant differences at p < 0.017. Group 1: Pin at the SF; Group 2: Pin 3 mm distal to the SF; Group 3: Pin 6 mm distal to SF with an inclined cranial-to-caudal direction

Fig. 5

Mediolateral radiographs of stifles following tensile testing. A, B Two representative specimens from Group 1 showing (A) comminuted distal tibial crest fracture and (B) transverse mid-tibial crest fracture with irregular fracture line. C Specimen from Group 2 with a transverse mid-tibial crest fracture passing through the pin tract. D Specimen from Group 3 with a distal tibial crest transverse fracture also involving the pin tract

Fig. 6

Illustrations of cross-sectional tibial crest anatomy and proximal pin positions planned for each experimental group. Transverse sections show progressive thinning of bone stock from proximal to distal regions, with the expected pin positions illustrated at (A) Group 1, (B) Group 2, and (C) Group 3. This anatomical depiction may help explain the observed group-specific differences in mechanical strength and fracture configurations