Mechanical contribution of the fibula to torsion stiffness and strength of the canine crus

Introduction
In humans, fibula was found to provide a small role in axial compression and torsion stability. To our knowledge, no experimental data are available regarding the mechanical contribution of the fibula to torsion stiffness and strength of the canine crus.

Materials and Methods
Thirteen specimens were divided in 2 groups and submitted to external torsional load until failure.
• I: Phase 1: tibiae and fibulae intact. Phase 2: fibulae intact after tibiae had already fractured.
• II: 1cm proximal ostectomy of the fibulae, with tibiae intact.
Specimens were tested at a constant 0.2degree/second rate. Working length and diameter of bones were measured. Torque and twist angle at failure were reported. Twist angle relative to working length and torsional stiffness were calculated. A Wilcoxon test was used to compare group I to group II. A p-value<0.05 was considered significant.
Results
Torque at failure of the fibula represented 6% of the torque of tibiae and fibulae combined. No significant differences were found between group I and II for twist angle relative to working length, ultimate torsional strength, ultimate twist angle and torsional stiffness.

Discussion / Conclusion
The twist angle at failure of the tibia of all specimens was comparable to data already published. The twist angle at failure of the fibula was much higher than the values reported in the literature. In the canine crus, contribution of the fibula to torsional strength and stiffness does not seem to be significant.