Effect of Wrist Splint Orthoses on Forearm Muscle Activity and Upper Extremity Kinematics

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Title: Effect of Wrist Splint Orthoses on Forearm Muscle Activity and Upper Extremity Kinematics
Author: Shu, Yu
Advisors: Gary A. Mirka, Committee Chair
David A. Dickey, Committee Member
David B. Kaber, Committee Member
Abstract: Ergonomics is concerned with understanding the interactions between humans and other elements in a system. Physical ergonomics is concerned with the prevention of musculoskeletal disorders (MSDs), - a topic of particular importance to industry because of the high costs of MSDS in worker' lost time, health care costs, worker' compensation, etc. Awkward postures have been identified as a risk factor in the development of several MSDs. In particular, awkward postures of the wrist are often the focus of intervention efforts. Wrist splint orthoses (WSOs) are intended to protect the wrist by limiting wrist motions and there have been reports of relief of wrist disorders such as carpal tunnel syndrome and tendonitis when the orthoses are worn at night. However, their use in work environments should be carefully considered because of the complex interaction of required wrist postures and the work environment/task. The focus of the current study was to evaluate the impact of wearing a wrist splint orthosis while performing tasks requiring deviated wrist postures. Ten subjects performed two experimental tasks. In the first experiment, the subjects performed a series of simple, single-plane wrist exertions at varied wrist angles (flexion/extension and ulnar deviations) with and without a wrist splint orthosis. Electromyographic (EMG) activity of three forearm muscles (flexor carpi radialis, flexor carpi ulnaris and extensor carpi ulnaris) were recorded as they performed these exertions. In the second experiment, upper extremity kinematics of the wrist, elbow, shoulder and torso were recorded as the subjects performed a simulated computer jumper installation task at varied work surface angles with and without a wrist splint orthosis. The results of the EMG experiment revealed a strong interaction between wrist angle and wearing a wrist splint orthosis. For example, at the neutral wrist posture, wearing a WSO did not elevate the normalized EMG of the studied muscles. At 48&deg; of wrist flexion, wearing WSO increased the normalized EMG of flexor carpi radialis by nearly 600% (32% of max vs. 5% of max, p<0.001). Similar trends were seen in deviated postures in other planes. In the study of the upper extremity kinematics during the jumper installation experiment, the results showed a strong effect (p<0.001) of the wrist splint on the shoulder abduction angle. Wearing WSO increased the shoulder abduction angle significantly (average 43.5&deg; vs. 32.3&deg;, p<0.01) during the jumper experiment indicating that the subjects adapted to the limited range of motion of the wrist by increasing shoulder movement. The results of this research provide important quantitative data relative to the recommendations of wrist splint utilization in the work environment to protect worker from occupational injuries and disorders. This study showed that wearing a wrist splint orthosis can increase the activity of the forearm muscles, thereby increasing exposure to another risk factor (force); and wearing the WSO can induce awkward postures in other parts of body, thereby increasing the risk of MSDs to other body regions. These results indicate that the practice of having a worker wear WSO during work activities should be carefully considered relative to task demands.
Date: 2005-02-22
Degree: MS
Discipline: Industrial Engineering
URI: http://www.lib.ncsu.edu/resolver/1840.16/2468

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