How kinematic disturbance in the deformed rheumatoid thumb impacts on hand function: a biomechanical and functional perspective

Purpose This study investigates the effects of kinematic disturbances in rheumatoid thumb on patient’s hand functions via objective and patient-perceived measurements. Method Twenty-one patients with rheumatoid arthritis (RA) and 21 healthy age- and gender-matched individuals were recruited to receive the objective evaluations, including the Purdue Pegboard Test, Jamar dynamometer, pinch-meter, Permanent Impairment Scale and self-administrated measurements, including the Health Assessment Questionnaire (HAQ) and Manual Ability Measure-36 (MAM-36). An electromagnetic tracking system was used to measure thumb kinematics. The differences in the measures between the RA and control groups and the dominant and non-dominant hands of the RA group were examined. The relationships between the thumb kinematics and hand functional capabilities, as well as impairment levels, were also explored. Results The RA group showed significantly smaller thumb movement capabilities and hand strength, as well as worse scores in hand dexterity, MAM-36 and HAQ than healthy controls. The movement workspace of the RA thumb showed moderate correlations with the factors of hand strength, dexterity, impairment scale, MAM-36 and HAQ scores. Conclusions The findings indicate deficits related to the movement capability of the RA thumb may negatively influence hand dexterity and functional hand performance, as well as life quality, for the patients with RA.Implications for Rehabilitation A deformed rheumatoid thumb might limit the movement workspace of the thumb and consequently impair the hand performance as well as the life quality. The dominant thumb of the RA patients might have greater structural and functional deterioration than the non-dominant side. Suitable joint protection strategies, exercises and orthotics should be early applied to the RA patients for preserving hand functions.