The instantaneous hinge axis - its reproducibility and use as an indicator for dysfunction.

This study investigated irregularities in hinge movement in 113 subjects. These irregularities were analyzed by computer with an instantaneous three-dimensional "screw axis method." The variation in hinge movement was measured by the dispersion of the hinge axis instant centers. Dispersion of instant centers was greater for muscle pain patients than for the normal, indicating that instant center data could make a contribution to diagnosis and treatment planning.