Biomechanical analysis of the canine hind limb: calculation of forces during three-legged stance

This paper presents a three-dimensional biomechanical model of the canine hind limb, and describes the process of determining the muscle forces and joint reaction forces and moments occurring in the hind limb during three-legged stance. The model was based on anatomical and morphometric data presented in a previous paper. Equations of equilibrium were formulated for the different components of the hind limb. Since the number of unknowns exceeded the number of equations, the problem was statically indeterminate. Two optimization techniques were applied to solve this statically indeterminate problem. The resultant hip-joint reaction force (acting on the acetabulum) predicted by these optimization methods ranged between 0.73 and 1.04 times body weight, and was directed dorsally, medially and caudally. The resultant knee-joint reaction force (acting on the femur) ranged between 1.05 and 1.08 times body weight, and was directed dorsally, laterally and cranially. The largest muscle forces predicted by the minimization of maximal muscle stress (MMMS) criterion were in the biceps femoris (0.24 times body weight), rectus femoris (0.15 times body weight), medial gluteal (0.18 times body weight), semi-membranosus (0.09 times body weight), the lateral and intermediate vastus (0.18 times body weight) and the medial vastus (0.17 times body weight). The largest muscle forces predicted by the minimization of the sum of muscle forces (MSMF) criterion were in the biceps femoris (0.29 times body weight), lateral and intermediate vastus (0.45 times body weight)), and the deep gluteal (0.16 times body weight). The magnitudes and directions of the forces in the joints of the canine hind limb, as well as in the muscles that surround these joints, provide a database needed for future biomechanical analyses of the physiology and pathophysiology of the canine hind limb.