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.