Effects of proximal femoral fixation method and joint angulation on simulated muscle forces in a canine limb press model.

Abstract

Objective: To quantify how increasing axial loads, femoral fixation methods (rigid vs. flexion-extension mobility) and joint angles reflecting early versus mid-stance impact simulated quadriceps and gastrocnemius forces.

Study design: Non-randomized, cadaveric experimental study.

Sample population: Unpaired canine pelvic limbs (n = 10) from adult large-breed dogs.

Methods: Limbs were mounted in a custom limb press with the femur sequentially rigidly fixed at 70° to horizontal or allowed flexion-extension. Quadriceps and gastrocnemius muscles were simulated with load cells and turnbuckles. Axial loads of 10%, 20% and 30% bodyweight (BW) were applied. Stifle and hock angles were sequentially fixed to represent mid- (135° and 145°) or early stance (145° and 135°). Outcome measures were BW normalized simulated muscle loads and their ratio. Data were analyzed using non-parametric repeated measures.

Results: Quadriceps and gastrocnemius forces increased with axial load (p < .001). Quadriceps force was unaffected by fixation method but showed higher mid-stance values in flexion-extension models at 20% and 30% loads (p = .03). Gastrocnemius force varied by configuration (p = .01) and showed significant load-configuration interactions (p = .003); mid-stance values were lower than early stance in flexion-extension models. Muscle force ratios were consistent across loads (p = .2) but differed by configuration (p = .02), with higher mid-stance values in flexion-extension models.

Conclusion: Femoral fixation method and stance configuration had limited impact on simulated muscle forces. Flexion-extension mobility did not substantially increase muscle loading.

Impact: Rigid femoral fixation remains a valid approach for canine limb press models.