Biomechanics and strength in the distal upper limb influence median nerve health in manual wheelchair users - SUMMARY. Development of best practices to prevent carpal tunnel syndrome (CTS) among manual wheelchair users is currently blocked by the scarceness of biomechanical analyses at the wrist. For example, despite comparable pain and injury prevalence, there are 8-fold more scientific publications focused on the shoulder than the wrist. To prevent CTS and preserve independence, there is a critical need to determine which patterns of forces and joint motions utilized by manual wheelchair users in their daily life injure the median nerve. The overall objective for this application is to establish that both the physical demands of wheelchair propulsion and musculoskeletal capacity affect median nerve health in manual wheelchair users with SCI. Our central hypothesis is that insufficient muscle strength, relative to the force applied by the hand to the handrim during propulsion, causes the declines in median nerve function that ultimately lead to CTS. Our rationale is that by establishing the balance between the physical demands of wheelchair propulsion and upper limb strength needed to protect median nerve health, we will enable clinicians to identify asymptomatic individuals at high risk for chronic nerve injury and to design preventative interventions that improve safety factors and decrease cumulative risk of developing CTS, such as targeted strengthening, or optimization of wheelchair fitting. In Aim 1, we will determine if clinical measures of median nerve health are better in manual wheelchair users with SCI who apply smaller handrim forces during propulsion. Enabled by our innovative markerless motion capture approach, we will measure both handrim force and wrist range of motion during overground propulsion in a large- scale (N=200), cross-sectional study. We hypothesize that people who apply smaller forces to the handrim during propulsion have healthier median nerves, which we will quantify via clinical nerve conduction tests. We will also test if wrist range of motion during propulsion – observable without any instrumentation on the participant or their wheelchair using our markerless methods – predicts handrim force. In Aim 2, we will determine the balance between handrim force and upper limb strength required to protect median nerve health. We will measure maximum grip, isometric wrist, and isometric pronation and supination strength among our 200 participants. We hypothesize that the ratio between handrim force and maximum grip strength increases with worse median nerve function, and we will evaluate whether including the other strength measurements improves our model of median nerve health. Development of personalized biomechanical models in Aim 3 will elucidate internal muscle loading in the distal upper limb during propulsion and provide the first assessment of the role of active muscle function in median nerve injury. Our innovative methods directly address the bottlenecks of marker-based methods that limit data generation and clinical translation. Combined with our interdisciplinary expertise, we are poised to collect an unprecedented amount of data, providing a new foundation needed to prevent the secondary condition of carpal tunnel syndrome in this already over-burdened population.
