Although rheumatoid arthritis (RA) patients frequently experience muscle weakness, limited information exists on disease specific muscle changes. The common hand deformity in RA includes disturbed finger extension with subsequent flexion deformities. The aims of this study were to measure finger extension force and finger flexion force in patients with rheumatoid arthritis and compare them with healthy subjects.  We also wanted to explore the possible causes of impaired finger extension force with the help of ultrasound muscle analyses.

The study group comprised of 40 women: 20 patients with RA (median disease duration 20 years) and 20 healthy age-matched controls. The finger extension force measurements were performed with a newly developed device (EX-it), finger flexion force was measured with the Grippit. The extensor digitorum communis muscle was examined with ultrasound.

Significant differences were found between the two groups, concerning extension and flexion force (p<0.001). Ultrasound measurements indicated significant differences in structural parameters (Cross Section Area (p< 0.05), muscle thickness (p < 0.05) and fascicle length (p < 0.05)). Overall changes in muscle architecture during contraction were more pronounced in the control group than in the RA group (p < 0.01).

The results indicate differences in structural parameters as well as functional tests, i.e. contraction time and extension muscle force capacity, between normal and RA muscles. Whether these differences depend on a disease-specific effect on the muscles in RA, or are secondary to inactivity or hand deformities, remains to be elucidated.