The Contribution of Different Tissues to Stiffness of the Wrist Joint

Passive articular stiffness is not only a function of articular tissues, but also tissues associated with movement, such as muscles and tendons. Allowance has been made for the relative contribution of these extra-articular tissues in comparing the resting stiffness of normal subjects and patients with rheumatoid arthritis. In addition, the stiffness of the muscle-joint complex with agonist/antagonist muscles co-contracting has been measured. Significant muscle wasting was found in rheumatoid arthritis (forearm muscle cross-sectional area for normals: 30.9 cm², for rheumatoid arthritis: 22.7 cm², p = 0.002). Allowing for this, there was a significant difference in resting stiffness between normals and rheumatoid arthritis subjects (adjusted resting stiffness normals: 90.8 × 10-³ Nm/deg, rheumatoid arthritis: 120.3 × 10-³ Nm/deg, p = 0.015). There was no difference between the groups in terms of the relationship between stiffness and grip at different levels of muscle co-contraction, suggesting the muscles are qualitatively normal in rheumatoid arthritis.