Abstract
Introduction:
Contemporary Posterior Cruciate Ligament (PCL) retaining TKA implants (CR) are associated with well-known kinematic deficits, such as absence of medial pivot motion, paradoxical anterior femoral sliding, and posterior femoral subluxation at full extension. The hypothesis of this study was that a biomimetic implant, reverse engineered by using healthy knee kinematics to carve the tibial articular surface, could restore normal kinematic patterns of the knee.
Methods:
Kinematics of the biomimetic CR and two contemporary CR implants (A, B) were evaluated during simulated deep knee bend and chair-sit in LifeModeler KneeSIM™ software. Anteroposterior motion of the medial and lateral femoral condyle centers was measured relative to a tibial origin. The implants were mounted on an average knee model created from magnetic resonance imaging (MRI) of 40 healthy knees. The medial and lateral collateral ligaments, posterior cruciate ligament, quadriceps mechanism, and the overall capsular tension were modeled. The soft-tissue insertions were obtained from the average knee model, and the mechanical properties were obtained from literature. In vivo knee kinematics of healthy subjects from published literature was used for reference.
Results:
During the simulated deep knee bend, the biomimetic CR showed knee motion similar to that reported for healthy knees in vivo, with an overall medial pivot and greater rollback of the lateral femoral condyle than the medial condyle (7.2 mm medial vs. 13.2 mm lateral, Fig 1. and Fig. 3). In contrast, contemporary CR-A showed no medial pivot rotation, and the femur underwent paradoxical anterior sliding from 0 deg to 90 deg flexion. Contemporary CR-B did not show paradoxical anterior femoral sliding. However, contemporary CR-B also did not show medial pivot and the posterior rollback of the medial femoral condyle was slightly greater than that of the lateral condyle (9.7 mm medial vs. 7 mm lateral). Similar trends were seen for all implants during the simulated chair sit (Fig 2. and Fig. 3).
Conclusion:
The results confirmed the hypothesis that, during the simulated activities, the biomimetic CR implant could provide kinematics similar to that reported for healthy knees, unlike contemporary CR implants. The biomimetic implant showed medial pivot motion with greater rollback of the lateral femoral condyle than the medial condyle. In contrast, the contemporary implants showed several abnormalities including absence of medial pivot, paradoxical anterior femoral sliding and reduced posterior rollback.
