(A-23) Impact of Age of Spinal Cord Injury on Peak Rotator Cuff Forces during Manual Wheelchair Propulsion: A Preliminary Analysis

Introduction:: Manual wheelchair usage is widespread (over 3 million users in the US) and serves as the primary method of mobility for many individuals with paraplegia after spinal cord injury (SCI) [1]. Manual wheelchair users with paraplegia have reported high incidence of shoulder pain. Shoulder pathology is associated with shoulder pain, with nearly all manual wheelchair users exhibiting some form of shoulder pathology through evaluative ultrasound [2]. Surprisingly, adults with pediatric-onset of SCI were found to have lower incidence of shoulder pain relative to adults with adult-onset of SCI despite having more years of wheelchair use [2]. Large rotator cuff muscle forces and glenohumeral joint contact forces presumably increase the risk for shoulder pain. Based on a greater occurrence of shoulder pain in individuals with adult-onset SCI, we expect that peak glenohumeral joint contact forces and rotator cuff muscle forces will be greater in these individuals relative to pediatric-onset SCI. The goal of our work is to determine the impact of age of SCI onset on peak rotator cuff muscle forces and glenohumeral contact forces during propulsion; here we present preliminary analyses.


Materials and Methods:: Three participants with paraplegia were selected from a larger cohort for preliminary analyses: a child (male, age 13.9 years), an adult with pediatric-onset SCI (male, 20.1 years) and an adult with adult-onset SCI (female, age 19.3 years). Marker trajectories, handrim forces, and EMG data were recorded as previously described by Schnorenberg et al., (2014) as participants propelled a wheelchair at their self-selected speed. A scapulothoracic shoulder model [3] was adapted to include forearm and wrist muscles from Saul et al. [4]. Musculoskeletal model scaling, inverse kinematics, a residual reduction algorithm, and computed muscle control were performed using OpenSim (version 4.3) to generate simulations that emulated the experimental kinematics and kinetics. Glenohumeral joint contact forces were calculated using a joint reaction analysis, which sums the forces transferred through the joint adjacent bodies.


Results, Conclusions, and Discussions:: Peak rotator cuff muscle forces over the propulsion cycle are presented in Table 1. EMG onset and offset timings aligned well with simulated muscle excitations (from computed muscle control) for most muscles.

Preliminary analysis suggests large variability between muscle forces and joint contact forces among the subjects. The forces we estimated are higher relative to other studies investigating patients with paraplegia [5]. However, the musculoskeletal model we used represents a robust shoulder model allowing for four degrees of freedom for the scapula, consists of separate muscle representations (e.g., for inferior and superior portions), and includes muscles spanning across the forearm [3-5].

Preliminary results suggest differences in shoulder muscle and joint forces during wheelchair propulsion among three subjects from our groups of interest: children, adults with pediatric-onset of SCI, and adults with adult-onset of SCI. Further analysis will lead to characterization of potential differences and help identify key factors that result in shoulder pain and pathology.


Acknowledgements (Optional): : Funding from the Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD) of the National Institutes of Health (award number R01HD098698).


References (Optional): : [1] Schnorenberg, A. J., et al., J. Biomech. 2014 47(1), 269–276. [2] Brose, S. W., et al., Arch Phys Med Rehabil 2008 89(11), 2086–2093. [3] Seth, A., et al., PLOS ONE 2016 11(1), e0141028. [4] Saul K, et al. Comput Methods Biomech Biomed Engin. 2015;18(13):1445–1458. [5] van Drongelen, S., et al., Arch Phys Med Rehabil 2005. 86(7), 1434–1440.