The validity and inter-relationship of subjective and objective measurements of stiffness in human joints

Abstract

Rheumatoid arthritis is a chronic, progressive, inflammatory disease characterised by pain, stiffness, swelling and loss of function. Severity of these symptoms is extremely variable both between patients and over time in individual patients. Assessment of disease activity and response to treatment relies heavily on subjective assessments of pain and stiffness and non-specific biochemical measures. In this study an arthrograph has been used to measure stiffness objectively at the right index metacarpal-phalangeal joint. Stiffness was defined as resistance to motion in the flexion / extension plane of movement. The finger was moved through 40 degrees, centred on the equilibrium position. Stiffness was quantified in terms of resistive torque, dissipated energy and angles of the hysteresis loop slope in flexion, extension and mid range positions. Principal components analysis was later used to create an ‘objective stiffness factor' from these readings. Grip strength, proximal inter-phalangeal joint size and total hand size were measured in all study subjects. Patients with rheumatoid disease were asked to assess the severity of their pain and stiffness using numerical rating scales and to record the duration of their morning stiffness. Joint tenderness was assessed using an articular index; plasma viscosity and haemoglobin estimation were recorded. One hundred healthy women and eighty five women with rheumatoid disease were each assessed on one occasion. Thirteen healthy women and twenty six women with rheumatoid disease agreed to be assessed monthly for one year. Objective stiffness was found to be influenced by size of the pip joints. It bore little relationship to patient’s subjective assessment of stiffness and did not differentiate between patients and healthy control subjects. Patient's assessment of their symptoms was mainly influenced by joint tenderness and grip strength. These findings support the suggestion that difficulty of movement, due to pain and weakness, is being misinterpreted as stiffness by patients with active rheumatoid disease.