The function of posterior tilt of the tibial component following posterior cruciate ligament-retaining total knee arthroplasty.

To increase the range of motion in the knee, posterior cruciate ligament-retaining total knee arthroplasty (TKA), which has a roll back (RB) mechanism, is used. The roll back mechanism is the complex movement of the femoral condyles relative to the tibial plateau, which results in translation of the tibiofemoral contact point posteriorly as the knee is flexed. This study was undertaken to assess the function of the posterior cruciate ligament (PCL) and posterior tibial tilt following PCL-retaining TKA. Eleven fresh-frozen cadaveric normal lower extremity specimens (average age: 75.4 years; range: 69 to 88 years) were obtained for this study. The test was performed on a loading frame after specimen preparation. The calcaneal bone was fixed on the rigid frame. A load of 9.5 kg was applied perpendicularly by the moving frame to femoral head through four casters. PCL strain and RB were measured before and following TKA by changing the posterior tilt of tibial component and the external rotation of femoral component. PCL strain at 105 degrees flexion in the 0 degree posterior tilt group (3.3% +/- 2.4%) was decreased in the 10 degrees posterior tilt group (0.6% +/- 0.5%), and this decrease was statistically significant (p < 0.05). RB was measured as anterior-posterior translation by using an arthroscopic probe. After TKA, RB was decreased in the medial compartment but was increased in the lateral component. These different movements of the tibiofemoral contact points consequently caused rotation in the flexion position. Posterior tilt of the tibial component decreased the efficiency of the PCL's function. Retaining the PCL physically is not the same as preserving the function of the PCL because of the lack of the ACL, the change of the joint line, the differences in articular geometry, and the balance of the ligaments.