Posterior stabilized (PS) total knees are regarded as one classification, although there are considerable differences in condylar and cam-post geometries which may affect their kinematic outputs. Evaluation methods for kinematics have included Oxford type machines [1], robots [2], knee simulators [3,4], computer models [5], and loading rigs specifically designed to measure laxity in line with the ASTM standard on constraint [6].

We developed a desktop machine for kinematic evaluation of total knee models under a full range of loading conditions and flexion angles, and proposed that the data from the anatomic knee be used as the benchmark [7].

Our hypotheses were that current PS designs will show a large variation in kinematic output, that these would differ from anatomic characteristics, and that an asymmetric guided motion design could potentially restore anatomic kinematics.

The test machine applied...

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