Musculoskeletal modeling of the shoulder and elbow in cervical spinal cord injury

Individuals with cervical spinal cord injury (SCI) lose voluntary control over their shoulder and elbow musculature. The extent of muscle paralysis depends on the level and type of injury. Rehabilitation interventions such as Functional Neuromuscular Stimulation may be applied to restore lost shoulder and elbow function. However, designing effective systems for the shoulder is difficult due to it mechanical complexity: multiple joints, redundant muscles about each joint, and multi-articular muscles. Musculoskeletal modeling can be a useful tool to gain insight into the shoulder biomechanics following cervical SCI and to facilitate the design of rehabilitation interventions. The goal of this work was to investigate shoulder function following cervical SCI and to evaluate the feasibility of restoring shoulder function in this population. This goal was achieved through experimental measurement of stimulated and voluntary shoulder function in individuals with cervical SCI and through simulations using a musculoskeletal model of the shoulder and elbow.; The major findings of this work were: (1) Successful restoration of shoulder function in high level cervical SCI using FNS relies on the availability of the adequate muscles for stimulation and on the magnitude of the forces obtained from electrical stimulation of these muscles. (2) It may be feasible to restore basic proximal arm function to individuals with high level cervical SCI with a set of only seven muscles and modest forces from each of these muscles. (3) Individuals with C5-C6 SCI have compromised shoulder function (limited shoulder abduction, scapular winging and lack of shoulder adduction and horizontal flexion) due to muscle paralysis. (4) Finally, it is possible to obtain reasonable estimates of maximum shoulder muscle forces in vivo based on external measurements of shoulder strength and muscle activation.; This work demonstrated the value of musculoskeletal modeling as a tool to investigate shoulder function and to design effective rehabilitation interventions.