Three-dimensional model of the feline hindlimb

This paper describes a three dimensional musculoskeletal model of the feline hindlimb based on digitized musculoskeletal anatomy. The model consists of seven degrees of freedom: three at the hip and two each at the knee and ankle. Lines of action and via points for 32 major muscles of the limb are described. Interspecimen variability of muscle paths was surprisingly low: most via points displayed a scatter of only a few millimeters. Joint axes identified by mechanical techniques as non-coincident and non-orthogonal were further honed to yield moment arms consistent with previous reports. Interspecimen variability in joint axes was greater than that of muscle paths and highlights the importance of joint axes in kinematic models. The contribution of specific muscles to the direction of endpoint force generation is discussed. The production of coordinated movement requires that the nervous system control muscle forces to generate joint torques required for control of the limb endpoint in Euclidean space. The nervous system must be capable of transformation between Euclidean space and joint space and between joint space and muscle space to determine what set of muscle activations is required to generate a desired motion (Lacquaniti and Maioli, 1994). Knowledge of thes