Instantaneous axis of rotation for continuous human knee motion

Abstract

Previous studies of human knee motion are based on finite rotation data collected using large rotation steps varying from 5 to 30 degrees. In some cases this rotation data is used to develop axes of rotation for the joint. For such analysis, the rotation axis developed may be significantly different from the joint's instantaneous axis of rotation because, in general, the axis of rotation developed using finite rotation steps only closely approximates the true instantaneous axis of rotation if the step size is small. For the current study, a device has been developed to record high frequency (15 Hz) rotation and translation data of the femur and tibia during knee flexion. Kinematic constraint equations have been developed to analyze the six degree of freedom rotation and translation data to obtain an accurate approximation to the instantaneous axis of rotation. Four cadaveric knees were II analyzed with all ligaments intact. Motion characteristics common to all knees were identified. The most obvious characteristic, internal tibial rotation, was related to the initial varus/valgus orientation of each knee. The anterior cruciate ligaments (ACL) of these same knees were subsequently severed, the knees were measured, and the motion analyzed. Differences in the motion characteristics of each knee were detected alter the ACL was cut