New instrumental set for the assessment of the hand functionality

Hand motor deficits have been widely investigated, and several devices have been proposed for the selective and accurate study of specific hand motor tasks. Most studies have focused on the four, long fingers. The thumb function, although extremely important for the performance of most daily activities involving the hand, has scarcely been documented. A set of general-purpose, instrumental measuring devices has been designed and constructed at the authors' laboratory to measure and monitor the force each finger exerts separately, under isometric conditions, during pressing tasks. More generally, it is meant for the functional evaluation of the normal hand in different postures, but it also provides reliable measurements of the injured or deformed hand. The instrumental set is suitable for both biomechanical research and clinical applications. Effectively integrated with a visual feedback tool, it could be exploited in delivering and monitoring custom-designed rehabilitation programmes. The characteristics of the force transducers (range 0-100 N) were: inter-axis crosstalk < 4%; non-linearity < +/- 0.4% f.s.; hysteresis < 0.3% f.s.; overall accuracy +/- 1% f.s. The overall measurement system resolution was better than 0.1 N, and the keys response to the mechanical shock (acquired at 10 kHz) showed a resonance frequency of about 1 kHz. It was observed that the thumb contributed more than 30% of the overall pressing force.