Effect of power-assisted hand-rim wheelchair propulsion on shoulder load in experienced wheelchair users: A pilot study with an instrumented wheelchair
Introduction
Incidences of shoulder overuse injuries among hand-rim wheelchair users are high with figures varying between 30 and 73% in the chronic spinal cord injury population [1], [2], [3]. It is suggested that part of the risk factors for overuse originate in wheelchair propulsion itself. Characteristics of hand-rim propulsion related to shoulder overuse injuries are the intensity of mechanical loading of the shoulder during the push phase, the highly repetitive nature of propulsion motions and force generation in extremes of shoulder motion [2], [4], [5], [6], [7], [8].
To create a better balance between mechanical loading and the work-capacity of the shoulder complex during propulsion, guidelines have been developed [9], [10]. These guidelines recommend minimum: push-frequency; maximum shoulder extension combined with internal rotation and abduction; imbalance in internal and external rotators at the shoulder; peak propulsion forces; and overall propulsion forces. Specifically, the radial directed forces at the rim, high posterior and lateral directed forces at the shoulder, and superior directed forces combined with internal rotation moments at the shoulder are deemed to be potential risk factors and therefore should be minimized [1], [6].
One of the guidelines [10] recommends a power-assisted wheelchair (hybrid between hand-rim and powered wheelchairs) [11] as a way to reduce energy expenditure in hand-rim wheelchair propulsion. However, research shows that power-assisted wheelchair propulsion applies to more aspects than energy expenditure alone [12]. Several studies compared hand-rim and power-assisted propulsion on kinematic and electrophysiological parameters [13], [14], [15], [16], [17], [18]. The results were promising in reducing the risk-factors of shoulder overuse injuries. Shoulder flexionāextension [15], [16] and internalāexternal rotation [13], [16] significantly decreased during power-assisted propulsion. Shoulder abduction tended to decrease, however, this was not significant [13], [15]. The results on push-frequency were ambiguous [13], [14], [15], [17], [18]. Muscle activity in the pectoralis major [16], [17], [19] and in the triceps brachii [16], [19] significantly decreased during power-assisted propulsion.
Although high forces and moments are important risk factors in the development of shoulder overuse injuries, little attention has been paid to the influence power-assisted propulsion could have on these risk factors. To our knowledge no previous studies reported the influence of power-assisted propulsion on shoulder kinetics and shoulder angles during peak force in actual hand-rim wheelchair users. Only 1 study with healthy subjects [16] combined kinematic and electrophysiological parameters with kinetics measured at the rim. This study showed that power-assisted wheelchair propulsion reduced the risk factors of wheelchair-related shoulder injuries in healthy novices [16]. However, before these results can be translated to clinical practice, additional research with experienced wheelchair users is necessary. This is essential, because differences in propulsion technique between experienced wheelchair users and novices are assumed. These differences may emerge from certain impairments (e.g. partly innervated upper extremity muscles, hypertonia) as well as the mere extend of hand-rim propulsion experience. Also, the effects of motor-learning during the measurement period of the healthy novices may cause additional differences [20]. Therefore, in this current study the measurements were done following a period of regular use in the personal daily environment. The aim of the current study was to compare hand-rim propulsion with and without power-assist on shoulder load in a group of experienced wheelchair users, while propelling an instrumented experimental wheelchair on a motor driven treadmill during standardized conditions. To get insight in the potential risk factors of shoulder overuse injuries we quantified shoulder load as: (1) intensity and frequency of forces and moments acting on the rim and the shoulder; (2) shoulder angles during force generation; (3) range of motion of the shoulder during the push; and (4) intensity of upper-extremity muscle activation. It is hypothesized that power-assisted hand-rim propulsion has a reducing effect on the above mentioned outcomes, i.e. potential risk factors for shoulder overuse.
Section snippets
Subjects
The sample size was based on our pilot study with healthy subjects [16], because patient data on our primary objective was lacking [12]. Based on the peak force on the rim, as outcome measure for the total amount of force necessary to propel a wheelchair, a sample size of 6 was deemed to be sufficient to detect changes with an alpha of 0.05 and a power of 0.80. The sample size was calculated with the statistical program G*Power version 3 (Heinrich Heine UniversitƤt DĆ¼sseldorf). We took into
Results
Eleven hand-rim wheelchair users, 6 men and 5 women with a mean age of 35.6Ā Ā±Ā 5.6 years, participated in this study. The hand-rim wheelchair was their primary mode of mobility for 12.2Ā Ā±Ā 9.6 years due to incomplete spinal cord injury (nĀ =Ā 4; height T1, T7, T9, T10), Ehlers Danlos (nĀ =Ā 2), hereditary spastic paraplegia (nĀ =Ā 3), cerebral palsy (nĀ =Ā 1), and Friedreich's ataxia (nĀ =Ā 1). The subjects had a mean height of 1.74Ā Ā±Ā 0.11Ā m and a mean weight of 67.6Ā Ā±Ā 15.3Ā kg.
All participants performed
Discussion
In this article shoulder load between hand-rim and power-assisted hand-rim propulsion were compared, while propelling an instrumented experimental wheelchair on a motor driven treadmill under standardized conditions. A comparison was made of (1) intensity and frequency of forces and moments acting on the rim and the shoulder; (2) shoulder angles during force generation; (3) range of motion of the shoulder during the push; and (4) intensity of upper-extremity muscle activation. To our knowledge,
Conclusion
According to the guidelines, in order to create a better balance between mechanical loading and the work-capacity of the shoulder complex during propulsion [9], [10], power-assisted propulsion on a treadmill is effective in reducing the majority of the potential risk factors of shoulder injury. During power-assisted propulsion the peak resultant force exerted at the hand-rim decreased and was performed with significantly less abduction and internal rotation at the shoulder. At shoulder level
Conflict of interest
The authors declare that there is no conflict of interest.
Ethical approval
This study was approved by the local medical ethics committee under reference number P11-03, and registered in the trail register under no. NTR2661.
Funding
This study was supported by INTERREG The Netherlands and Germany (European Regional Development Fund of the European Union), grant no. 34 Interreg IV A.
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