The Measurement of Stiffness in the Rheumatoid Hand

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Abstract
Previous attempts to measure stiffness objectively are reviewed. A major limitation of the earlier studies using arthrographs is the lack of definition of the equilibrium position of the joint. Other devices which claim to measure stiffness indirectly also fail to define this characteristic of the joint, and this omission may cause misleading results. We have measured stiffness in 135 patients with rheumatoid arthritis (RA) and have compared this group with 128 normal subjects. In addition we have measured stiffness over a 24 hour period in a further 14 subjects with RA. Mean values for resistive torque were 72.9 Nm. per degree in RA and 81.6 Nm. per degree in normals (Ns), for hysteresis 32.6 per cent in RA and 36 per cent in normals ( P < 0.001), and for equilibrium position 5.6 degrees ulnar deviation in RA and 3.2 degrees ulnar deviation in normals ( P < 0.001). The difference in hysteresis values is probably due to the muscular wasting consequent on chronic RA. Stiffness variables did not show evidence of circadian variation, but there was evidence of a change in equilibrium position into ulnar deviation in the early hours of the morning. The symptom of early morning stiffness may well be due to this change in equilibrium position coupled with muscular factors and fluctuations in pain intensity.