Fig. 12

Schematic representation of the human knee with its potential force carrying structures: muscles, ligaments, and bony contacts that can contribute to the resultant inter-segmental joint forces and moments. Mathematically, this represents an indeterminate system as the resultant inter-segmental joint forces and moments represent 2 independent vector or 6 independent scalar equations with 16 force contributing elements whose force magnitude and direction result in potentially 48 unknown scalar values. Even assuming that only the muscular forces contribute substantially to the intersegmental resultant joint moment and that the direction of the muscle force vectors, and the associated moment arm vectors (direction and magnitude), are known at any instant in time, still results in a highly indeterminate system of equations with an infinite number of possible solutions for most everyday human (sub-maximal) movements. (Adapted from Crowninshield and Brand [73], with permission)