title: Limited forearm motion compensated by thoracohumeral kinematics when performing tasks requiring pronation and supination.
abstract: 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.
authors: Musculoskeletal Research Laboratories, Department of Orthopaedic Surgery, Yong Loo Lin School of Medicine, National University of Singapore, Singapore.
authors: Barry P
authors: BP
authors: Pereira
authors: Ashvin
authors: A
authors: Thambyah
authors: Taeyong
authors: T
authors: Lee
mesh_terms: D000222:Adaptation, Physiological / Q000502:physiology; D005260:Female; D005542:Forearm / Q000502:physiology*; D006801:Humans; D006811:Humerus / Q000502:physiology*; D008297:Male; D009068:Movement / Q000502:physiology*; D011403:Pronation / Q000502:physiology*; D016059:Range of Motion, Articular / Q000502:physiology*; D013484:Supination / Q000502:physiology*; D013647:Task Performance and Analysis; D013909:Thorax / Q000502:physiology*; D055815:Young Adult