The shoulder joint is the most commonly reported site for pain and magnetic resonance images conducted on the shoulders of veterans with various levels of spinal cord injury have indicated early signs of rotator cuff disease, premature joint degeneration, as well as abnormalities surrounding the coracoacromial arch. Recent studies have shown that excessive use of the upper extremities in performing everyday tasks like wheelchair propulsion and transfers is related to the onset of shoulder pain and injury. However, existing knowledge about the mechanical function of the shoulder necessary to perform every day tasks is very limited. This is mostly due to fact that intrinsic muscle forces and moments cannot be measured directly.
The purpose of this non-hypothesis driven collaborative project is for both Cleveland and Pittsburgh VA Centers to work together to address the limitations of current modeling efforts and provide a level of detail that would further aid in identifying the predisposing factors that lead to overuse injuries in wheelchair users. To date we have developed a realistic, individualized geometric model of the shoulder bones using MRI imaging and software to create a 3D computer model. We are currently working on FEA model of the shoulder complex that will incorporate the MRI model of the shoulder bones. Our next steps are to add supporting structures, create the FEA mesh, and implement the critical configuration (position of the bones at maximum propulsion force), material properties, and boundary conditions. The stress and strain distribution through the elements making up the FEA shoulder model may provide insight into the mechanisms responsible for the pain and injury commonly reported among wheelchair users. The model may also assist in identifying ways to propel the wheelchair or configure the wheelchair to minimize stress and strain on the shoulder joint.