Total knee arthroplasty kinematics. An in vivo evaluation of four different designs.

Thirty-four patients who had 42 total knee arthroplasties during the past 5 years were examined. Four types of total knee arthroplasties (Tricon-M, PCA, Variable Axis, and Anametric) were evaluated, using a computerized knee evaluation system. The patients and 10 controls with normal knees were tested for anteroposterior stability with the Lachman test, medial/lateral stability at 20 degrees, varus/valgus stability at 20 degrees, internal/external rotation at 80 degrees and 20 degrees of flexion, and internal/lateral rotation (screw home) over the active range of motion. At 30 degrees of flexion, the Variable Axis prosthesis was 54% more constrained than the normal knee to anterior/posterior shear. The Anametric and the Variable Axis were more lax under varus/valgus stress than the normal knee by 85% and 71%, respectively. There were no statistical differences for any of the other tests.