Shoulder biomechanics and muscle plasticity: implications in spinal cord injury

After spinal cord injury, excessive burden falls on the upper extremity, especially the shoulder. Overall, 51% of persons with spinal cord injury have shoulder problems. Common shoulder problems in persons with spinal cord injury begin with muscle imbalance that can lead to glenohumeral instability, impingement disease, rotator cuff tears, and subsequent degenerative joint disease. These problems can be attributed to the functional demands placed on the shoulder that are specific to patients with spinal cord injury, including overhead activities, wheelchair use, and transfers. Despite preventive exercises, shoulder problems in persons with spinal cord injury remain a significant problem, causing pain and functional limitations. The biomechanics of the shoulder for persons with spinal cord injury resulting from changes in muscle plasticity will be elucidated. Specifically, the effects of scapular protraction that can result from muscle imbalance, the age-dependent properties of the anterior band of the inferior glenohumeral ligament, and the influence of the dynamic restraints around the shoulder will be addressed.