Numerical Analysis of Musculotendinous Forces and Joint Reaction Forces during Motion of Index Finger.

In this paper, an optimal method of numerical analysis was proposed for the musculotendinous forces and joint reaction forces in the index finger. The finger model at each position in motion was constructed taking three dimensional locations and directions of all musculotendons into account. The bones were modeled as massless rigid bodies, and each musculotendon was as a straight element from the origin to the insertion. A Iocal orthogonal coordinate system at each finger joint was used to define force and moment. Because the control mechanism of the finger is very complex, musculotendinous forces and joint reaction forces can not be calculated by only the static equilibrium equations of force and moment. The SQP method of the non-linear optimization was applied to solve this statically indeterminate problem. The results obtained from this analysis gave good agreements with well-known physiological phenomena. The optimal finger position, at which the sum of musculotendinous forces was the minimum, was determined in tip-loaded finger motion like touchtyping motion. The findings are very important to understand the functional anatomy and pathologic deformities of the hand as well as to develope a prosthetic design for finger joints.