Modification of the posterior cruciate ligament tension following total knee arthroplasty: comparison of the Genesis CR and LCS meniscal bearing prostheses

Aim: A biomechanical study was conducted to determine the in-vitro modification of the posterior cruciate ligament tension following different types of total knee arthroplasty (TKA). Materials and methods: The Genesis CR (non-mobile tibial inlay, n=9) and LCS meniscal bearing prostheses (mobile meniscal bearings, n=8) were compared with the human cadaveric knee joint. Posterior cruciate ligament (PCL) tension was assessed with implantable force transducers. A six-degree-of-freedom manipulator was used to measure knee kinematics at 10° intervals from 0° to 120° of flexion with [300 Newton (N)] and without load application (0 N). Statistical analysis was performed with the Wilcoxon rank sum test. Results: Analysis of the PCL tension following TKA using the Genesis CR prosthesis revealed a non-significant (P=0.20) decrease of transducer output with load (300 N) and a non-significant (P=0.73) increase without load (0 N). Concerning the LCS meniscal bearing prosthesis a significant (P=0.01) decrease of transducer output was assessed with load (300 N) whereas a non-significant (P=1.0) modification was seen without load (0 N). Conclusion: The Genesis CR prosthesis allows PCL tension to be close to normal as the knee flexes, which is contradictory to the assumed evidence for a missing restorability of a regular PCL tension after TKA. Our results hence indicate, that the effected tension of the PCL strongly depends on the balance and interaction between design of the implant and the functional role of the retained PCL.