Limited Forearm Motion Compensated by Thoracohumeral Kinematics When Performing Tasks Requiring Pronation and Supination

in Journal of Applied Biomechanics
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This study investigates the altered thoracohumeral kinematics when forearm rotation is restricted while performing five activities requiring pronation and supination. Two splints simulated both a fixed-supinated or fixed-neutral forearm in six healthy subjects; the three-dimensional coupled relationship among motion about the forearm, elbow, and shoulder were analyzed. In using a screwdriver, the normal range of forearm rotation of 77.6° (SD = 30.8°) was reduced in the fixed-supinated to 11.3° (SD = 2.9°) and fixed-neutral to 18.2° (SD = 6.2°). This restriction from the fixed-supinated and fixed-neutral forearms was compensated at the shoulder by a significant increase in the total range of (1) ad/abduction by 57.3° and 62.8° respectively (p < .001), (2) forward-reverse flexion (24.3° and 18.2° respectively; p < .05) and (3) internal-external rotation (37.1° and 44.2° respectively; p < .001). A similar result was demonstrated for the doorknob activity. The elbow did not significantly contribute to forearm rotation (p = .14), and is believed to be due to the elbow axis being orthogonal and oblique to the forearm axis. For open kinetic-chain activities, with a fixed-supinated forearm performing there was a significant coupled increase in ad/abduction (p < .05) and int/external rotation (p < .05) for the phone and feeding tasks, with the phone task also having a significantly increased forward shoulder flexion (p < .05). For the fixed-neutral forearm, significant compensatory movement was only seen in the feeding task with increased ad/abduction and internal-external shoulder rotation (p < .05) and the card inserting task with increased ad/abduction and forward-reverse shoulder flexion. Limited forearm function requires compensatory motion from adjacent joints to perform activities that require pronation and supination. This study quantifies the compensatory mechanism about the shoulder in a forearm limited in prosupination.

Barry P. Pereira (Corresponding Author) is with the Musculoskeletal Research Laboratories, Department of Orthopaedic Surgery, Yong Loo Lin School of Medicine, National University of Singapore, Singapore. Ashvin Thambyah is with the Musculoskeletal Research Laboratories, Department of Orthopaedic Surgery, Yong Loo Lin School of Medicine, National University of Singapore, Singapore, and with the Department of Chemical and Materials Engineering, Faculty of Engineering, University of Auckland, New Zealand. Taeyong Lee is with the Faculty of Engineering, Department of Bioengineering, Laboratory for Biomedical Mechanics and Materials, National University of Singapore, Singapore.