Comparison of knee joint functional laxity after total knee replacement with posterior cruciate-retaining and cruciate-substituting prostheses

The objective of this study was to measure three-dimensional knee motion or functional laxity with implants which either retained the posterior cruciate ligament (PCL+) in ten patients, or substituted for excised PCL with a posterior stabilized articulating surface (PCL-S) in ten patients. The intent was to identify the specific influence and significance of the presence of the PCL under active flexion and extension. Internal-external rotation (screw home movement) and anterior-posterior translation (femoral rollback phenomena) with active extension and flexion were chosen to characterize knee joint functional laxity, and were measured using an instrumented spatial linkage. Knees with a PCL+ implant exhibited both screw home movement and femoral rollback, while knees with a PCL-S design exhibited only femoral rollback. A knee with a PCL+ implant was more able to reproduce the normal kinematics of the screw home movement and femoral rollback, compared to a PCL-S design.