RESNA 26th International Annual Confence
It is commonly thought that individuals utilizing a customized seating system will have better postural support for their pelvis and trunk and will therefore have better use of their upper extremities than if they use a non-customized seating system. The goal of this study was to investigate this hypothesis in subjects with Multiple Sclerosis (MS). Ten subjects with MS were tested in both a customized and non-customized seating system on 10-degree tilted surface.
Due to fatigue and balance problems, people with MS are often forced to use mobility aides to accomplish daily life activities. Motorized wheelchairs and scooters are prescribed for people with MS based on their level of disability, with the more severely disabled individuals being provided a customized wheelchair. Upper extremity tests including functional reach (1) and item movement tests (e.g. Jebsen test (2)) have been used to evaluate upper extremity function. In previous studies, functional reach has been used to analyze the influence of the wheelchair cushion, seat angle and the use of belts on individuals in seating systems. (3). Item movement tests examine either the time or the number of items moved. However, some of these tasks, such as the Jebsen can-stacking test, require a minimum degree of dexterity in order to be completed. Based on the studies mentioned before, larger functional reaches, shorter completion times and greater numbers of items moved were indicators of a better seating system. Other tools used to analyze the seating system have included the seat center of pressure (COP) (4), where smoother trajectories were related to a better seating system. No studies have taken into account the analysis of upper limb trajectory and its correlation to trunk movement.
It was hypothesized that performance in a customized seating system (wheelchair) is better than in a non-customized seating system (scooter). The following measurements were used to define performance: total path length of upper extremity movement, trunk excursion and center of pressure excursion during both a forward/lateral reach and an elliptical path test.
10 subjects with MS were enrolled in the study. The subjects were predominantly male (90%) with an average age of 56.4±11.7 years. All subjects used a powered mobility aid and had adequate gross motor function to perform the tasks. Eight of the subjects regularly used motorized wheelchairs with custom seating, one subject used a scooter and one used both. The same scooter was used for all subjects that utilized power wheelchairs exclusively. For the one subject without a wheelchair, a wheelchair was provided with customized seating. All subjects were educated about the study and signed an informed consent before the study was conducted.
The Peak motion analysis system (Peak Performance Technologies, Inc.) with six 60 Hz cameras and a 19-marker set was used to evaluate posture and upper extremity function. Three markers were placed on the seating system. The other 16 markers were placed on the bony prominences of the subject's body. A pressure-mapping device (Force Sensor Array by Vista Medical) was used to collect the pressure distribution, at 10 Hz, on the seat, as well as COP location. An electronic triggering device was used to synchronize data acquisition. Subjects completed the sequence of tasks, shown in Table 1, in both seating systems (randomized order) with a 30-minute rest period between tests. The tests were performed on a 10-degree surface, tilted with the dominant side higher, in order to challenge trunk endurance and strength. When testing in an unfamiliar seating system, a 10-minute period of acclimatization was given to the subjects. Two pressure relief push-ups were performed at 5-minute increments before each task.
For the reaching and the elliptical path tasks, the following quantities were calculated: the average of lateral and forward average trunk excursion angles, total path length and the Root Mean Square (RMS) of the lateral and forward COP displacement. In addition, the average of the maximum COP displacement was calculated for the reaching tasks. For the can-stacking test, completion time was recorded. Parametric (student t-test) and non-parametric t-tests (Wilcoxon) were performed to evaluate the results. Non-parametric t-tests were used when the magnitude of the skewness was greater than one.
Significant differences were seen for the angular measurements for the lateral and forward reaching task. A 2.5º decrease was present on the average trunk flexion/extension angle when the task was performed in the scooter. No significant differences were found on the frontal COP movement. Lateral COP excursion in the scooter, during the initial reaching task was greater than in the wheelchair. During the elliptical path test, the COP movement in the lateral direction had a greater RMS value in the wheelchair. No significant differences were found in the can-stacking test.
Of the performance measures evaluated, only the lateral center of pressure excursion during the elliptical path test was significantly greater in the customized seating system. There were no differences in total path length of upper extremity excursion and trunk excursion. It appears that subjects depend on the seat cushion and their leg and trunk strength during frontal excursion. However during lateral excursion, the back and lateral components of the seating system are important because of the lateral trunk support, making the pelvis stable and allowing the subjects to perform better. In addition, during the frontal reaching, the COP measures do not completely represent the trunk movement since part of the body weight is being transferred to the legs. The lateral RMS of the COP shows that there is more deterioration in the lateral COP excursion when the scooter is used during a longer task (elliptical path task).
The overall premise of the study was based on clinical observations by seating professionals. These observations suggest that there is compromised upper extremity function and chronic postural deterioration when persons with MS are seated in a non-customized seating system. Since our study looked at performance over a 4 hour period, chronic changes may not be identifiable. Another limitation may be that the measures we chose to test our hypotheses are not sensitive enough to demonstrate differences. Other shortcomings include the small sample size, the variability in the impairments among people with MS, and the fact that 80% percent of our population used a wheelchair as a primary mobility aid.
This study was funded by The Pittsburgh Veterans Health Administration, Rehabilitation Research & Development, Centers of Excellence Program. The motion analysis was performed at the HPL, Rehabilitation Medicine - Physical Therapy Program, University of Colorado HSC.
Dept. of Mechanical Engineering.
University of Colorado at Denver
P.O. Box 173364
Denver, CO 80217