The role of hypoxia in rheumatoid hand disease

The factors thought to be responsible for ulnar drift of the digits in patients with rheumatoid arthritis (RA) are either external forces applied to the fingers during normal usage of the hand or changes in the internal forces/anatomy of the digits due to alterations in the supporting structures of the joints and/or their control mechanisms. The part played by the intrinsic muscles in the development of ulnar drift is obscure; their tightness may be due to adaptive shortening or a disease process. A consistent feature of the rheumatoid process is hypoxia of the involved joints, tendons and associated synovium. Our hypothesis is that intrinsic muscle hypoxia may also be responsible for the loss of intrinsic function observed in many patients with ra disease, which then contributes to the development of the characteristic deformities of ra hand disease. We have taken measurements of tissue oxygen levels in the intrinsic muscles of the hand of patients with a diagnosis of RA undergoing elective surgery at Mount Vernon Hospital using the microelectrode technique established for measurement of synovial tissue oxygen. Patients undergoing elective hand surgery for conditions other than RA served as matched controls. Results so far suggest that the hand muscles of ra patients are significantly (p<0.05) more hypoxic (mean oxygen tension 6.7%) than the matched controls (mean oxygen tension 10%) and there is a trend of increasing hypoxia with the RA sub-group in the radial-to-ulnar direction. Therefore, it is possible that the weakness and wasting of the intrinsic muscles of the hand observed in RA are not the result of atrophy secondary to joint disease but may be due to primary muscular involvement due to hypoxia. Ethical approval has been granted for this study.