Wheeled Mobility Biomechanics

Background: Rates of shoulder pain in individuals who use manual wheelchairs (MWCs) as their primary means of mobility have been reported to be as high as 70% during activities of daily living. Current prevailing thought is that mechanical impingement of the soft tissues that reside within the subacromial space between the humeral head and coracoacromial arch is a major contributor to the shoulder pain in users of MWCs. The subacromial space size is directly related to the kinematics at the shoulder joint. Yet to be answered are questions about which common daily tasks are characterized by the most potentially detrimental kinematics.

Objective: The purpose of this analysis was to quantify and compare potentially detrimental kinematics in three common tasks performed by individuals with spinal cord injury and shoulder pain. These data will add to the body of knowledge and test common assumptions about relative risk of tasks.

Design: A cross-sectional study of 15 MWC users with shoulder pain.

Methods: Electromagnetic surface sensor measures of mean and peak scapulothoracic (ST) internal and downward rotation, anterior tilt, and glenohumeral (GH) internal rotation were compared across propulsion, weight relief, and scapular plane abduction tasks using one-way repeated-measure ANOVA.

Results: Statistical differences were observed between the tasks for all rotations. Mean ST anterior tilt was greater in weight relief and propulsion than during scapular plane abduction (24°, 23°, and 13° of anterior tilt, respectively). Mean GH axial rotation during weight relief was more internally rotated than during propulsion and scapular plane abduction (9°, 26°, and 51° of external rotation, respectively).

Limitations: Surface-based measures of kinematics are subject to skin motion artifact, especially in translation which was not addressed in this study.

Conclusion: Each task presented with specific variables that might contribute to risk of developing shoulder “impingement” and pain. These data may assist therapists in their assessment of movement contributions to shoulder pain in this population, as well as in subsequent treatment planning.

Studies of manual wheelchair propulsion often assume bilateral symmetry to simplify data collection, processing, and analysis. However, the validity of this assumption is unclear. Most investigations of wheelchair propulsion symmetry have been limited by a relatively small sample size and a focus on a single propulsion condition (e.g., level propulsion at self-selected speed). The purpose of this study was to evaluate bilateral symmetry during manual wheelchair propulsion in a large group of subjects across different propulsion conditions. Three-dimensional kinematics and handrim kinetics along with spatiotemporal variables were collected and processed from 80 subjects with paraplegia while propelling their wheelchairs on a stationary ergometer during three different conditions: level propulsion at their self-selected speed (free), level propulsion at their fastest comfortable speed (fast), and propulsion on an 8% grade at their level, self-selected speed (graded). All kinematic variables had significant side-to-side differences, primarily in the graded condition. Push angle was the only spatiotemporal variable with a significant side-to-side difference, and only during the graded condition. No kinetic variables had significant side-to-side differences. The magnitudes of the kinematic differences were low, with only one difference exceeding 5°. With differences of such small magnitude, the bilateral symmetry assumption appears to be reasonable during manual wheelchair propulsion in subjects without significant upper-extremity pain or impairment. However, larger asymmetries may exist in individuals with secondary injuries and pain in their upper extremity and different etiologies of their neurological impairment.