Biomechanics of the upper extremity during wheelchair propulsion and weight relief raise in wheelchair users with spinal cord injury

This dissertation tests hypotheses regarding scapular kinematics, upper extremity control and load distribution during manual wheelchair propulsion in wheelchair users with paraplegia and tetraplegia. The purpose of the first study was to determine if wheelchair users with tetraplegia and paraplegia modify the distribution of load across the elbow and shoulder when propelling a manual wheelchair under customary and self-selected fast conditions. Wheelchair users with paraplegia and tetraplegia used the shoulder joint the prime means for wheelchair propulsion. By aligning the resultant force with the upper arm under the self-selected fast speed conditions, users with paraplegia and tetraplegia were able to attenuate the increases in shoulder net joint moments associated with increases in pushrim forces at self-selected fast velocities. The results of this study illustrated a technique for redistributing the load within the upper extremity that was independent of user's functional capacity.;The purpose of the second study was to determine if the magnitude of peak rim impact force at contact was dependent on the type of hand trajectory pattern during wheelchair propulsion. Kinematic (50Hz) and kinetic (2500Hz) data were collected on 34 wheelchair users. The four hand trajectory patterns were analyzed based on velocity prior to contact, peak impact force and the effectiveness of force at impact. A high correlation was found between the impact force and the relative velocity of the hand with respect to the wheel (p<0.05). Wheelchair users with paraplegia were found to have higher effectiveness of force at impact as compared to users with tetraplegia (p<0.05). No significant differences in the impact force magnitudes were found between the four observed hand trajectory patterns. Overall force effectiveness tended to be associated with injury level of the user rather than hand trajectory pattern.;The purpose of the third study was to determine the effect of load on the kinematics of the scapula of manual wheelchair users. Data was collected on 18 male participants (11 with paraplegia and 7 with tetraplegia) using an electromagnetic motion tracking system (100 Hz) and force sensing pushrim (200Hz). The participants propelled under no-load and loaded conditions at their customary propulsion velocity. This experiment is the first at determining dynamic scapular kinematics during wheelchair propulsion and differentiating the scapular kinematics between users with paraplegia and tetraplegia. Study four was designed to determine the feasibility of bent trunk propulsion technique observed in the first study. Wheelchair users with paraplegia (n=11) were asked to propel a wheelchair at their customary velocity when sitting normally and when leaning forward (shoulder positioned more anterior than normal). Analyzing the average net joint moment data no significant differences in the magnitude and distribution of shoulder and elbow net joint moments (NJM) was observed. However analysis of individual data showed that 4 of 10 users displayed a decrease in the NJM at the shoulder of as much as 50%. The other users either showed no change or slight increase in NJMs. The experiment determined that leaning forward does not necessarily cause a reduction in shoulder moments, a redirection of the force vector with respect to the segments is essential for success of this technique.;The purpose of the fifth study was to determine scapular kinematics and subacromial space when sitting and when performing a weight relief raise. Experienced wheelchair users with paraplegia (n=11) participated in the study. The kinematics of the right arm and trunk were recorded at 100Hz. All 11 users displayed similar directions of motion of scapula around all three axes of rotation while performing a weight relief raise. The overall range of angular rotation of the scapula was between 5--25 degrees with least amount of rotation observed in the protraction/retraction direction. The average reduction in subacromial distance (distance between the acromion and the shoulder joint center) was 41% (high of 70%) which occurred during the lifting phase, the subacromial distance increased back to the normal distance while the subject's held their weight during the holding phase of the weight relief lift. A reduction in subacromial distance may prove to be a potential indicator of risk of scapular impingement. (Abstract shortened by UMI.)...