A transducer for the measurement of finger joint moments

A device capable of simultaneously measuring the isometric moments generated about the metacarpophalangeal (MP), proximal interphalangeal (PIP), and distal interphalangeal (DIP) joints of all four fingers has been developed. The design utilizes a four-bar linkage to transmit moments, but not forces, to the device. This linkage allows the same device to fit a wide range of hand sizes without recalibration. The device was constructed out of aluminum bars which are strapped to each joint segment and to the back of the hand. Strain gauges mounted to the aluminum bars measure the bending moment on the device, which is directly related to the moment applied about the joint center of rotation. Because of the unique design of the device, it is not necessary to have accurate measurements of the joint center of rotation in order to get accurate moment information. A single device is capable of generating independent measurement of MP extension/flexion, PIP extension/flexion, and DIP extension/flexion. Four of these devices can be used to make simultaneous measurements of all the moments generated by all four fingers. The device also acts as a splint, allowing each joint to be positioned and locked at any angle through the range of motion of the joint. The device is accurate to within +/- 5.6% of each reading for moments from 10 N x cm to 100 N x cm and within +/- 2.0 N x cm for moments of 10 N x cm or less. If the device configuration is constrained, the accuracy can be improved to +/- 0.8% of full scale (100 N x cm) and +/- 0.21 N x cm for moments of 10 N x cm or less. The device can measure both flexion and extension moments up to 100 N x cm, and can allow the joints to be fixed at any angle from approximately 10 to 80 degrees.