Abstract
This paper describes a method of the three-dimensional numerical analysis for the musculotendinous forces and joint reaction forces of the index finger and the thumb during the tip pinch and the precision grasp. The bones were modeled as massless rigid bodies, and each musculotendon was as a straight element from the origin to the insertion. A local orthogonal coordinate system at each joint was used to define the constraint forces and moments. Because the control mechanism of the finger is very complex, no musculotendon and joint reaction forces can be calculated by only the static equilibrium equations of forces and moments. The SQP method was applied as the non-linear optimization method to solve this statically indeterminate problem. The results obtained from this analysis gave good agreements with well-known physiological properties. The optimal finger position, at which the total of musculotendinous forces was the minimum, was determined during the tip pinch and the precision grasp. The findings are very important in understanding the functional anatomy and pathologic deformities involving the hand and developing a prosthetic design for finger joints.
