Articular stiffness is an important symptom in most arthritic diseases and appears to be a useful marker of disease activity in rheumatoid arthritis. Attempts to obtain a reliable objective measure of articular stiffness span the last 30 years but a meaningful measure
of this symptom remains elusive. A number of reasons have been suggested to explain the discrepancy between objective and subjective stiffness in arthritis and these can be
summarised as: a semeiological confusion, aberrant mechano-receptor thresholds and concurrent muscle wasting. This thesis examines each of these hypotheses.
Some patients may confuse pain and stiffness or may wish to use other words to describe their joint symptoms. A questionnaire was developed which enabled patients
to express their joint symptomatology using a wide range of descriptors. No differences were found between health professionals and patients in their definition of each of the descriptors. The questionnaire discriminated clearly between groups of patients with rheumatoid arthritis, ankylosing spondylitis and non-articular rheumatism.
Movement perception threshold was measured in the finger but it was found that subjects relied on cutaneous information. Vibration perception threshold was used as
an alternative measure of mechano-receptor thresholds: no abnormalities were found in 50 patients with rheumatoid arthritis.
Muscle cross-sectional area was calculated from anthropometric data and the results compared with measurements obtained from computed tomographic scans. A
significant decrease in forearm muscle cross-sectional area was found in rheumatoid arthritis but the decrease was not sufficient to explain the reduction in grip strength
observed, some of the variation being explained by deformity and pain in the joints. From this study it was possible to make a correction for muscle wasting in previously published stiffness data, revealing significant increases in metacarpo-phalangeal joint stiffness in rheumatoid arthritis. This result was confirmed in new data based on the resonant frequency of the wrist. Further data on the qualitative aspects of muscle were obtained by relating dynamic angular wrist stiffness to level of contraction of forearm muscles. Although arthritic subjects differed significantly from normals at maximum activation, when the results were expressed in terms of absolute grip strength no differences were found, suggesting inhibition of muscle activation in rheumatoid arthritis.
It is concluded that symptomatic stiffness is objectively quantifiable in arthritis providing measurements are made in relationship to the equilibrium position of the joint
and providing a correction is made for muscle wasting.