Identification of key pinch forces required to complete functional tasks.

Reconstructive hand surgeries restore key pinch to individuals with pinch force deficits caused by tetraplegia. Data that define the magnitudes of force necessary to complete functional key pinch tasks are limited. This study aims to establish target pinch forces for completing selected tasks that represent a range of useful functional activities. A robot arm instrumented with a force sensor completed the tasks and simultaneously measured the forces applied to the task objects. Lateral pinch force requirements were calculated from these measured object forces. Pinch force requirements ranged from 1.4 N to push a button on a remote to 31.4 N to insert a plug into an outlet. Of the tasks studied, 9 of 12 required less than 10.5 N. These pinch force requirements, when compared to pinch forces produced by 14 individuals with spinal cord injuries (with and without surgical reconstruction of pinch), accurately predicted success or failure in 81% of subject trials. The prediction errors indicate a need to measure other factors such as pinch opening, force location, force direction, and proximal joint control.