Shoulder pain and wheelchair propulsion biomechanics in manual wheelchair users

Introduction: Shoulder pain remains a common health concern among nonathletic and athletic manual wheelchair users. The biomechanical parameters of wheelchair propulsion are thought to be associated with shoulder pain symptoms, yet the specific relationship between shoulder pain and either daily or sports wheelchair propulsion biomechanics is currently not well understood. In this thesis, four experimental studies addressed daily and sports wheelchair propulsion biomechanics and sought to identify associations between shoulder pain and the biomechanical characteristics of propelling a wheelchair in manual wheelchair users.

Methods: Shoulder pain was evaluated using the Performance Corrected Wheelchair User’s Shoulder Pain Index (PC-WUSPI). All laboratory testing was conducted with the participants own wheelchair (daily and/or sports) on a dual-roller wheelchair ergometer. A 10 camera Vicon motion capture system (Vicon, Motion Systems Ltd. Oxford, United Kingdom) collected three-dimensional kinematics of the upper limbs and thorax at 200Hz during the propulsion trials. The first study investigated whether the biomechanical characteristics of daily propulsion differ between a group of athletic (n =25) and nonathletic (n = 14) wheelchair users (Chapter 4). Subsequently, the association between shoulder pain severity and daily wheelchair propulsion biomechanics was examined in a diverse cohort (n = 40) of manual wheelchair users (Chapter 5). Chapter 6 investigated the longitudinal association between within-subject changes in shoulder pain and alterations in wheelchair propulsion biomechanics in manual wheelchair users at two timepoints separated by 4 to 6 months. Finally, the biomechanical characteristics of submaximal and high-intensity sports wheelchair propulsion and associations with shoulder pain were examined (Chapter 7).

Results: Despite differences in physical activity, there were no significant differences between kinetic or kinematic parameters of daily wheelchair propulsion between athletic and nonathletic wheelchair users. During daily wheelchair propulsion, those wheelchair users with moderate shoulder pain displayed significantly lower scapular kinematic variability (~ 1 °) compared to those with mild or no pain. This occurred between 17 - 51% of the push phase for internal rotation, between 31 – 42% and 77 – 100% of the push phase for downward rotation and between 28 – 36% and 53 – 65% of the push phase for posterior tilt (Chapter 5). Several longitudinal associations were reported between within-subject changes in shoulder pain and alterations in wheelchair propulsion biomechanics (Chapter 6). Wheelchair users with increased shoulder pain exhibited significantly lower peak torque variability (5 %) and greater peak glenohumeral abduction (9°) at baseline compared to the no-change group. They also displayed within subject alterations of greater contact angle (+ 8°), thorax range of motion (ROM) (+ 2°) and movement variability, but reduced peak torque (-1.5 Nm), shoulder ROM and peak angles over time. On the other hand, the propulsion biomechanics of those with no change/decreased pain remained unaltered. Finally, wheelchair athletes displayed significantly greater peak glenohumeral abduction and peak scapular internal rotation during the acceleration (20 ± 9° and 45 ± 7°) and maximal velocity (14 ± 4° and 44 ± 7°) phases of sprinting, respectively compared to submaximal propulsion (12 ± 6° and 39 ± 8°). In addition, greater shoulder pain severity was associated with larger glenohumeral abduction ROM (r = 0.59, P = 0.007) and scapular internal rotation ROM (r = 0.53, P = 0.017) during the acceleration phase of wheelchair sprinting, but with lower peak glenohumeral flexion (r = -0.49, P = 0.030), peak abduction (r = -0.48, P =0.034) and abduction ROM (r = -0.44, P = 0.049) during the maximal velocity phase. 

Discussion: Lower scapular variability displayed by wheelchair users with moderate shoulder pain may reflect a more uniform distribution of repeated subacromial tissue stress imposed by propulsion. This suggests that lower scapular kinematic variability during propulsion is associated with shoulder pain and may either contribute towards the development of shoulder pain or result from higher levels of shoulder pain. The alterations in wheelchair propulsion biomechanics displayed by individuals with worsening shoulder pain may provide an early indication that wheelchair users exhibit a protective short-term wheelchair propulsion biomechanical response to increases in shoulder pain which may temporarily help maintain functional independence. Associations with shoulder pain during sports wheelchair sprinting indicate that athletes with shoulder pain make kinematic alterations during the acceleration phase of the sprint that may further harm the shoulder, but modifications during maximal velocity may serve to protect the shoulder. However, interpretation of these biomechanical alterations should be made carefully as changes in these findings represent associations with shoulder pain and not causal inference. Despite the statistically significant angle differences reported in this thesis, the magnitude of these differences was relatively low, particularly in Chapter 5. Consequently, the meaningfulness of these differences may be limited from a clinical perspective, further work is required before these findings can be usefully translated to practice. Nevertheless, the findings of this thesis indicate that both kinetic and kinematic variability may be relevant variables for further investigation into daily propulsion using longitudinal and intervention studies. Future studies are recommended to incorporate detailed kinematic and kinetic analyses when assessing the biomechanical characteristics of the maximal velocity phase and acceleration phase of wheelchair sprinting.