Development of an OpenSim shoulder model for manual wheelchair users with tetraplegia

INTRODUCTION Extended manual wheelchair use has been associated with repetitive strain injuries in the shoulder and has been identified as a contributing factor to upper limb pain experienced by manual wheelchair users with spinal cord injury (SCI) [1]. Due to the nature of their SCI, individuals with tetraplegia (formerly quadriplegia) may be at an even greater risk for developing shoulder injuries because they often have only partial innervation of their shoulder, scapular, and thoracohumeral muscles [2]. Attempts to understand shoulder injury during wheelchair propulsion have included investigations of electromoyography (EMG) and kinematics. Mulroy et al. [3] utilized fine wire EMG to identify the shoulder muscles at greatest risk for fatigue, by examining muscle activation and recruitment patterns, during wheelchair propulsion. Newsam et al. [4] investigated three-dimensional upper extremity motion generated by manual wheelchair users with tetraplegia and paraplegia. Expanding upon their work, Dubowsky et al. [5] developed the first computer graphics-based model for wheelchair propulsion. This unique model was an active visual representation of the movement, as opposed to passive plots of shoulder kinematics and muscle activity, from which movement patterns had to be interpreted. Unfortunately, it included surface EMG as inputs and was developed for manual wheelchair users with paraplegia. Our aim was to build upon these previous studies to develop an OpenSim [6] shoulder model for wheelchair propulsion in individuals with tetraplegia. OpenSim is open-source software that incorporates kinematic, kinetic, and EMG data as inputs to generate a dynamic simulation. The novelty of our model is that it is the first model to include fine wire EMG and an upper limb joint coordinate system in accordance with the International Society of Biomechanics standards [7]. Our model could potentially impact the clinical diagnosis, cause and treatment of shoulder injury for manual wheelchair users with tetraplegia.