A new force measurement device for evaluating finger extension function in the healthy and rheumatoid arthritic hand

Although often neglected, finger extension force is of great importance for developing grip strength. This paper describes the design and evaluation of a new finger extension force measurement device (EX-it) based on the biomechanics of the hand. Measurement accuracy and test-retest reliability were analysed. The device allows measurements on single fingers as well as all the fingers (excluding the thumb) of both healthy and deformed hands. The coefficient of variation in the device was 1.8% of the applied load, and the test-retest reliability showed a coefficient of variation no more than 7.1% for healthy subjects. This study also provides reference values for finger extension force in healthy subjects and patients with rheumatoid arthritis (RA). Significant differences were found in extension strength between healthy subject and RA patients (men, p < 0.05 and women, p < 0.001). EX-it provides objective and reliable data on the extension force capacity of normal and dysfunctional hands and can be used to evaluate the outcome of therapeutic interventions after hand trauma or disease.