A laboratory study of the effects of wrist splint orthoses on forearm muscle activity and upper extremity posture

OBJECTIVE: To evaluate the effects of wrist splint orthoses (WSOs) on forearm muscle activity and upper extremity/torso postures. BACKGROUND: WSOs are ubiquitous in industry, but the literature as to their biomechanical effects is limited. METHOD: Study 1: Participants performed single-plane wrist exertions with or without a WSO while the electromyographic (EMG) activity of the flexor carpi radialis, flexor carpi ulnaris, and extensor carpi ulnaris was captured. Study 2: Participants performed simple computer jumper installation tasks with or without a WSO while upper extremity/torso postures were recorded. RESULTS: Study 1: A significant interaction between WSOs and wrist angle was observed in the response of forearm muscles (e.g., normalized EMG of the flexor carpi radialis increased from 4.2% to 15.9% as flexion increased from 0 degree to 36 degrees in the orthosis conditions, whereas in the no-orthosis condition it remained approximately 5% at all wrist flexion angles). Study 2: WSOs were found to effect wrist, torso, and shoulder postures, with the orthoses creating a 48% decrease (36 degrees vs. 18.6 degrees) in wrist flexion and 80% decrease (15 degrees vs. -3 degrees) in ulnar deviation but at a cost of increased shoulder abduction of 22% (36.5 degrees vs. 44.5 degrees) and increased lateral bend of torso of 30% (6 degrees vs. 7.8 degrees). CONCLUSIONS: WSOs increased forearm muscle activity at large wrist deviation angles and induced awkward shoulder postures in tasks requiring significant wrist deviation. APPLICATION: Use of WSOs in occupational settings should be carefully considered relative to task requirements, as orthoses may do more harm than good.