Integration of marker and force data to compute three-dimensional joint moments of the thumb and index finger digits during pinch.

This study presents methodology to determine joint moments of the digits of the hand during pinch function. This methodology incorporates steps to identify marker-based kinematic data defining aligned coordinate systems for individual digit segments and joint centre locations. The kinematic data are then transformed to a common reference frame along with the force data collected at pinch contact of a customised apparatus in three dimensions. These methods were demonstrated with a pilot investigation to examine the static joint moments occurring during two-digit oppositional precision pinch at a particular end point force level applied at the digit pads. Notable abduction joint moments at the proximal joints of both digits were observed, which implicate the role of respective intrinsic and extrinsic muscles in maintaining pinch grasp. Examining differences in joint moment results when substituting selected steps of this methodological approach suggested greater relative importance for joint centre identification and segment coordinate system alignment.