Case Western Reserve University and Cleveland VA FES Center, Cleveland, OH, USA* Delft University of Technology, Delft, The Netherlands
Following cervical spinal cord injury (SCI) muscles of the hand, arm and shoulder become paralyzed. The remaining voluntary control over arm movement varies depending on the level and extent of the injury. Individuals with high level cervical SCI (C4 and above) retain very little voluntary control over arm function, limited to shoulder shrugging and pro-retraction. These individuals depend on attendant care for all activities of daily living. Individuals with SCI at the C5-C6 levels of the spinal cord have voluntary control over some muscles of the shoulder and elbow. However, the scope of their hand workspace is limited by paralysis of key shoulder and elbow muscles that prevent them from positioning the hand in front of the trunk or to actively adduct the shoulder. These deficits in arm function prevent these individuals from performing important activities of daily living including bimanual tasks and wheelchair transfers.
Current efforts in our lab are aimed toward adapting a musculoskeletal model of the shoulder and elbow to reflect cervical SCI. The model (Van der Helm et al., J. Biomech, 27(5): 551-569) was developed based on able-bodied individuals. The SCI model will be used to gain a better understanding of shoulder function following SCI and to aid in the development of new rehabilitation interventions using functional neuromuscular stimulation (FNS) combined with muscle tendon transfers to restore shoulder and elbow function in this population. Experimental procedures and analysis techniques have been designed and are currently being implemented to obtain parameters for the model that reflect the voluntary maximum muscle forces in individuals with C5-C6 SCI. The analysis techniques have been validated using simulations of the proposed experimental measurements. Finally, a method based on simulations with the musculoskeletal model is being implemented to obtain the minimum number of muscles and the maximum muscle forces required to allow performance of a specific set of tasks in individuals with high- level tetraplegia.