Function can sometimes be restored to patients with movements disabilities via surgical reconstruction of musculoskeletal structures. Surgical reconstructions, however, often compromise the capacity of muscles to generate force and moment about the joints. Patients that cannot generate sufficient joint moments are left with weak or dysfunctional limbs. The goal of this dissertation is to understand the connection between the parameters of various surgical procedures and the moment-generating capacity of the lower-limb muscles.

A graphics-based model of the human lower limb was developed to study the effects of musculoskeletal reconstructions on muscle function. The lines of action of forty-three muscle-tendon complexes were defined based on their relationships to three-dimensional bone surface models. A model for each muscle-tendon complex was formulated to compute its force-length relation. The kinematics of the lower limb were defined by modeling the hip, knee, ankle, subtalar, and metatarsophalangeal joints. Thus, the maximum isometric force and joint moments that each muscle-tendon complex develops can be computed at any body position. Since the model is implemented on a computer graphics workstation, the model parameters can be graphically manipulated according to various surgical techniques. For example, the origin-to-insertion path of a muscle-tendon complex can be altered to simulate a tendon transfer. The results of the simulated surgeries are displayed in terms of presurgery and postsurgery muscle forces, joint moments, and other biomechanical variables.

The model of the lower limb has been used to analyze tendon surgeries and pelvic osteotomies. The analysis of tendon lengthenings indicated that the forces generated by the ankle plantarflexors are extremely sensitive to surgical lengthening of tendon;​ other muscles are much less sensitive. Quantifying the sensitivity of the muscle forces and joint moments to changes in tendon length provides important new data needed to design effective tendon surgeries. Simulations of the Chiari pelvic osteotomy suggest that osteotomies performed with high angulation shorten the hip abductors and may lead to the commonly observed weakness of the hip abductors. Simulated surgeries showed that horizontal osteotomies preserve the moment-generating capacity of the hip abductors and may therefore decrease the number of patients who limp after surgery.

Just as computer graphics systems have enhanced other areas of design and analysis, and interactive, graphics-based model of the human lower limb can facilitate the design and analysis of surgical procedures.