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A simulating analysis of the effects of increased joint stiffness on muscle loading in a thumb.

Authors
Wu-JZ; Li-ZM; Cutlip-RG; An-KN
Source
Biomed Eng Online 2009 Dec; 8:41
NIOSHTIC No.
20036361
Abstract
Background: The development of osteoarthritis (OA) in the hand results in increased joint stiffness, which in turn affects the grip strength. The goal of the present study is to theoretically analyze the muscle forces in a thumb in response to the increased joint stiffness. Methods: The thumb was modeled as a linkage system consisting of a trapezium, a metacarpal bone, a proximal and a distal phalanx. Nine muscles were included in the model: flexor pollicis longus (FPL), extensor pollicis longus (EPL), extensor pollicis brevis (EPB), abductor pollicis longus (APL), flexor pollicis brevis (FPB), abductor pollicis brevis (APB), the transverse head of the adductor pollicis (ADPt), the oblique head of the adductor pollicis (ADPo), and opponens pollicis (OPP). Numerical tests were performed using an inverse dynamic approach. The joints were prescribed to an angular motion at one degree-of-freedom (DOF) each time with all other DOFs of the joints being mechanically constrained, while the muscle forces in response to the joint motions were predicted. The normal joint stiffness was assumed to be 0.05, 0.10, and 0.15 N m/rad for interphalangeal (IP), metacarpophalangeal (MCP), and carpometacarpal (CMC) joint, respectively. The joint stiffness was assumed to increase by 50% and 100%, simulating the biomechanical consequences of OA. Results: Our simulations indicated that the increase in joint stiffness induced substantial increases in muscle forces, especially in the EPL and FPL muscles in response to IP, MCP, or CMC extension/ flexion motions. Conclusions: Because the strength of the muscles in the fingers is limited, the muscles will not be able to overcome joint resistance if joint stiffness is increased to its limit due to OA. This may contribute to the reduced range of motion typically seen in OA.
Keywords
Biodynamics; Biological-effects; Biological-function; Biological-monitoring; Biomechanical-engineering; Biomechanical-modeling; Biomechanics; Bone-structure; Ergonomics; Exposure-assessment; Exposure-levels; Exposure-methods; Hand-injuries; Muscle-function; Muscle-physiology; Muscle-stress; Musculoskeletal-system; Musculoskeletal-system-disorders; Osteogenesis; Physical-reactions; Physiological-effects; Physiological-fatigue; Physiological-response; Physiological-stress; Physiological-testing; Repetitive-work; Statistical-analysis
Contact
John Z Wu, National Institute for Occupational Safety and Health (NIOSH), Health Effects Laboratory Division, 1095 Willowdale Rd., Morgantown, West Virginia 26505
Publication Date
20091216
Document Type
Journal Article
Email Address
jwu@cdc.gov
Fiscal Year
2010
NTIS Accession No.
NTIS Price
ISSN
1475-925X
NIOSH Division
HELD
Priority Area
Construction
Source Name
Biomedical Engineering Online
State
WV
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