The fibula contributes minimally to torsional stiffness and strength of the canine crus in an ex vivo study in Beagles

Objective: To characterize the torsional mechanical properties of the canine crus, determine the contribution of the fibula to crus stiffness and strength under torsional loading, and describe the associated failure pattern. Methods: This ex vivo study was conducted from December 2021 through June 2022 and included 13 pelvic limbs from skeletally mature Beagles. Specimens were assigned to 2 groups: intact tibia and fibula (n = 7) and tibia with proximal fibular ostectomy (6). Crura were potted proximally and distally. Torsional loading was applied under quasi-static conditions until failure. Torque and twist angle at failure, torsional stiffness, and rotation relative to working length were recorded. Results: All specimens sustained mid-diaphyseal oblique/spiral tibial fractures. Mean torque to failure was 17.33 ± 2.95 Nm in intact crura, 18.45 ± 3.36 Nm following fibular ostectomy, and 1.13 ± 0.6 Nm for isolated fibula. No significant differences were detected between groups for any measured variable. Following tibial fracture, the isolated fibula exhibited minimal torsional stiffness and sustained 6.5% of the torque at failure of the intact crus. Conclusions: The fibula contributes minimally to the torsional stiffness and strength of the canine crus under torsional loading. The torsional mechanical properties of the canine crus were primarily determined by the tibia, and failure was consistently characterized by tibial fracture preceding fibular failure. Clinical Relevance: Fibular integrity appears to have limited influence on torsional stability in canine tibial fractures, although it may remain important for maintaining limb alignment and fracture management.