Upper extremity load during wheelchair-related tasks in subjects with a spinal cord injury

Stefan van Drongelen, MsC (Researcher)
DirkJan Veeger, PhD (Project leader)
Lucas van der Woude, PhD (Project leader)
Thomas Janssen, PhD
Edmond Angenot, MD

On December 9, 2005, Stefan van Drongelen, defended his dissertation entitled: Upper extremity load during wheelchair-related tasks in subjects with a spinal cord injury

Summary

Physical activity is seen as a powerful tool to increase the general health of people with a spinal cord injury (SCI) [66]. The downside of increased physical activity in subjects with a SCI is that it is more or less limited to upper-body work while the upper extremities are particularly sensitive to overload injury. Prevalence rates of 50 to 70% for upper extremity complaints have indicated that overload injuries of the musculoskeletal system are indeed a serious long-term problem [7,19] in subjects with a SCI. Especially, subjects with a high-level injury appear to be at risk due to a reduced muscle mass in the upper extremities [31,148].

The aim of this thesis is to increase the understanding of the underlying mechanisms related to the development of overload injuries of the upper body musculoskeletal system in subjects with a SCI.

In chapter 2, the prevalence of upper extremity musculoskeletal complaints and especially shoulder complaints was investigated. One hundred and sixty nine subjects with a SCI were measured and interviewed at four test occasions during and after their rehabilitation. To explain the number of pain complaints, these were related to lesion - and personal characteristics as well as to muscle force (MMT) and functional outcome (FIM motor score). This study showed that pain complaints already developed during the first months of rehabilitation, and that these were decreased by 30% at the time subjects were discharged. After the rehabilitation period no further decrease was found, but rather a slight increase. Subjects with tetraplegia had a higher risk factor of 2.8 for upper extremity complaints when compared to subjects with paraplegia. On the other hand, subjects with a 10 point higher FIM motor score had an 11% lower risk on upper extremity complaints and 12% on shoulder complaints. The same effect was found for the muscle score: subjects with a 10 point higher muscle score had a 14% lower risk on shoulder complaints.

Another interest of this study was to investigate whether personal characteristics led to a higher risk on developing upper extremity pain one year after the rehabilitation. It was found that pain at the beginning of the rehabilitation and a higher body mass index were strong predictors for pain one year after the inpatient rehabilitation.

Wheelchair propulsion and wheelchair-related tasks are both mentioned as risk factors for the development of upper extremity complaints in subjects with a SCI. Both activities have to be frequently performed for mobility and independence from the beginning of the rehabilitation onwards. For wheelchair propulsion the mechanical load has already been studied, but information about the load on the shoulder and the muscles during wheelchair-related activities of daily living was limited. In chapter 3 a description was given of the mechanical load of wheelchair propulsion, reaching, propelling up a slope, negotiating a curb and performing a weight-relief lift, quantified as net moments around the shoulder and elbow. The main interests were the magnitude of the moments and the differences between subjects with paraplegia, subjects with tetraplegia and able-bodied subjects. It was found that the net shoulder moments for the weight-relief lift and negotiating a curb were significantly higher when compared to the other tasks. Further, reaching and riding on a slope caused higher moments compared to level wheelchair propulsion. For the shoulder moments no significant differences were found between the three subject groups. From this study it could be concluded that the wheelchair-related tasks cause a high mechanical strain on the shoulder and elbow, but somewhat surprisingly, there were no differences between able-bodied subjects and subjects with paraplegia or tetraplegia.

It was expected to find differences between the subject groups because subjects with tetraplegia have muscle paralysis of various muscles of the upper extremity and of the thorax. They have to compensate for this paralysis with alternative muscles, which may have unfavourable torque components that have to be compensated again. Since additional muscle force cannot be detected from net moments, the tasks were also studied in a more detailed approach with a parameter for mechanical load that does incorporate these muscle forces as well as the strain on the glenohumeral joint. This joint reaction force not only reflects forces needed to overcome the external force but also the summed muscle forces around the joint. The joint reaction force could be calculated with the Delft Shoulder and Elbow model, which is an inverse biomechanical model of the upper extremity. This model also calculated the forces in the individual muscles.

In chapter 4 it was investigated whether the joint reaction forces and the muscle forces were higher for subjects with tetraplegia compared to subjects with paraplegia and able-bodied subjects for three different tasks. In this study it was put forward that there were differences among these subject groups. The different task performances were probably brought about by the muscle paralysis and the decreased stability in subjects with a high-level spinal cord injury. Especially the weight-relief lift seemed to be a task where stabilization of the shoulder and thorax is compulsory. The different task performances led to higher muscle forces and a higher joint reaction force. During wheelchair propulsion and reaching the peak muscle forces did not exceed 20% of the relative maximal force. For the weight-relief lift the latissimus dorsi, the biceps brachii and the monoarticular part of the triceps showed relative muscle forces up to 40% of their maximum force. Muscles, which apply high forces are at risk for overuse injuries.

In chapter 4, muscle paralysis was not included in the model, but the study already showed a difference in the magnitude of the joint reaction force due to differences in task performance. Would account be taken of muscle paralysis, the differences were expected to be even higher, since unfavourable muscles have to compensate for muscle paralysis. In chapter 5, the model, which was used in chapter 3 and 4, was modified to represent subjects with a high-level SCI. The maximum relative force of the muscles was adjusted for the different lesion levels (C5 -TI), based on the assumption that the maximum force was relative to the number of innervating segments of the muscle above the lesion. The segment innervations for the muscles were based on Gray [54]. Results showed that the difference in task performance led to a higher joint reaction force for the subjects with tetraplegia. Surprisingly the effect of the different lesion levels was small: values were only 7% higher for the C6 lesion compared to the T1 lesion, which in fact was the intact model. It appears that the subjects with tetraplegia already performed the weight-relief lift in an economic, but different manner, given their lesion level. Besides lesion level, also paralysis of the triceps muscle was studied 'in this chapter. As expected, it was found that the triceps is an important muscle for the performance of the lift for the able-bodied subjects. They needed around 30% of the maximum force to successfully perform the lift, while lifting following the technique used by the subjects with tetraplegia only 10% of the triceps force was needed.

These studies showed that weight-relief lifting is a highly straining task for the shoulder. In chapter 6 it was investigated whether this task led to a reduction of the subacromial space. During this task there is a large downward gravity force on the trunk, which has to be compensated by activity of the thoracohumeral muscles. When these muscles cannot generate sufficient force, the subacromial space might decrease, which could lead to impingement of the supraspinatus tendon and surrounding tissue against the acromion. In previous studies different force ratios of the shoulder muscles were found for subjects with impingement when compared to subjects without impingement. Therefore, in this study not only the muscle activity was measured, but isometric force of the muscle groups as well. Unfortunately, neither a reduction in the subacromial space, nor differences in the force ratios could be detected between the able-bodied subjects and the subjects with paraplegia. Explanations for these results might be that subjects with impingement or shoulder pain were not included in this study or that there is indeed a high inter-individual variability in the subacromial space. During this task the thoracohumeral muscles as well as the triceps caput longum showed levels of muscle activity between 25 and 50% of their voluntary maximum. The activity of these muscles was higher for subjects with paraplegia compared to the able-bodied subjects.

In chapter 7, the epilogue, the main findings of the studies described in this thesis were summarized and discussed. The results of the studies contributed to a better understanding of the risk on overuse injuries of the upper extremity in subjects with a SCI. The peak load during wheelchair-related tasks like weight-relief lifting was found to be high and possibly damaging for the soft tissues. Since lesion level did not influence the load a great deal in the subjects with tetraplegia it is suspected that they perform the weight-relief lift and possibly also other tasks in the most economic way, considering their lesion.

Of course peak load is only one risk factor for overuse injuries. Further research must show what the influence is of continuous submaximal exercise on the occurrence of damage. Detection of mechanical, physiological and biological markers in an early phase of overuse can contribute to the prevention and treatment of these injuries.

Strengthening the muscles, in a highly balanced manner, and improving the overall physical capacity for subjects with a SCI is assumed to be necessary to reduce the relative load. Although exercise is proven to be good for general health and can reduce the risk on secondary impairments, especially for subjects with tetraplegia there appears to be a fine line between improving health and overload as a result of exercise. Further, the need for other, less straining techniques of the lift and transfer is stressed. In addition, improved assistive technology and built environment from early rehabilitation onward is important to reduce the external load.

Publications from this thesis

Upper extremity musculoskeletal pain during and after rehabilitation in wheelchair-using persons with a spinal cord injury. Van Drongelen S, de Groot S, Veeger HE, Angenot EL, Dallmeijer AJ, Post MW, van der Woude LH. Spinal Cord, 44(3): 152-9, 2006
Mechanical load on the upper extremity during wheelchair activities. Van Drongelen S, van der Woude LH, Janssen TW, Angenot EL, Chadwick EK, Veeger HE. Arch Phys Med Rehabil 86(6): 1214-1220, 2005.
GH contact forces and muscle forces evaluated in wheelchair related ADL in able-bodied vs. persons with paraplegia and tetraplegia. Van Drongelen S, van der Woude LH, Janssen TW, Angenot EL, Chadwick EK, Veeger HE. Arch Phys Med Rehabil. 86(7): 1434-40, 2005.
Glenohumeral joint loading in tetraplegia during weight-relief lifting: a simulation study. Van Drongelen S, van der Woude LH, Janssen TW, Angenot EL, Chadwick EK, Veeger HE. Clin Biomech, 21(2): 128-37, 2005