Abstract
Introduction
Total-knee-arthroplasty (TKA) is a well-established method to restore the joint function of the human knee. Different types of TKA designs are clinically available which can be divided in two main groups, the posterior-cruciate- ligament (PCL) sacrificing and retaining group. However, pre-operatively it is often difficult to plan for one or the other. Therefore, the research question was: Is it possible to develop a TKA bearing design which works for both the cruciate sacrificing and retaining technique? A medial-congruent (MC) bearing design was developed, characterized by a high medial sagittal conformity and lower lateral sagittal conformity, which can be used for both cruciate ligament states. This study compares the laxity and kinematics of this MC design to a contemporary PS design for the cruciate sacrificing technique and to a contemporary CR design for the cruciate retaining technique.
Methods
Four specimen-specific computer models of the human knee, consisting of a femur, tibia and fibula bone as well as the contribution of the ligaments and capsule, were virtually implanted with three TKA designs in four constellations: 1) MC without PCL, 2) MC with PCL, 3) contemporary PS without PCL and 4) contemporary CR with PCL following the design specific surgical technique and tibia slopes. Laxity tests in internal-external rotation (moment ± 4 Nm) were performed with the implanted models for a weight bearing case (500N compression). In addition, a high demanding activity (lunge) was simulated. The resulting averaged laxities and kinematics were analysed and compared to each other.
Results
When sacrificing the PCL, MC showed lower medial laxity throughout flexion and higher lateral laxity above 60° flexion compared to the PS design. When retaining the PCL, the MC resulted in lower medial laxity throughout flexion, lower lateral laxity in extension and similar lateral laxity in flexion compared to the CR design. When sacrificing the PCL in the lunge activity, the MC design had a more posterior position throughout flexion on both condyles until deep flexion when the engagement of the cam/spine occurred for the PS design and posterior motion of the medial condyle during mid-flexion as opposed to anterior motion for the PS design. When retaining the PCL in the lunge-activity, the MC design had a more posterior position throughout the activity, and similar medial and lateral condyle motion throughout flexion compared to the CR design.
Conclusion
When sacrificing the PCL, MC behaved similar to a contemporary PS design with more medial stability, more lateral laxity in deep flexion, and a posterior position during a lunge activity that did not depend on a cam/spine mechanism. When retaining the PCL, MC behaved similar to a contemporary CR design with more medial stability, similar lateral laxity in deep flexion, and a posterior position during a lunge activity demonstrating that the increased medial conformity did not cause a kinematic conflict with the retained PCL. These findings illustrate the concept that the MC design can be used for both the PCL sacrificing and retaining technique.
