Resultant finger joint loads in selected activities

The intersegmental loads transmitted by the proximal interphalangeal (PIP) and metacarpophalangeal (MCP) joints of the index finger are presented in activities involving application of a twisting moment by the hand. Twenty normal subjects, ten males and ten females were included in the studies. A six component load transducer was incorporated in each of the two fixtures representing a water tap and a jar cap 70mm in diameter and the maximal loading on the fingers was monitered in applying an isometric twisting moment to these structures. Two different hand configurations were studied for each activity: the spatial position and orientation of the finger segments were determined using two orthogonally positioned still cameras, and specially designed stick markers were utilized to highlight anatomical landmarks. The results confirm the use of the finger in a complex three-dimensional manner with no significant differences between the male and female subjects. Forces recorded in the jar cap activity were larger than those applied in the tap activity, the maximum being around 100 N and in general the abduction/adduction moments developed at both joints were of comparable magnitude to flexion/extension. Torques as high as 0.6 Nm and 1.0 Nm were calculated at the PIP and MCP joints respectively.