Abstract
Introduction
Posterior cruciate ligament (PCL) preservation in total knee arthroplasty (TKA) is adovocated on the grounds that it provides better restoration of knee joint kinematics as opposed to PCL sacrifice. Mobile-bearing (MB) total knee prostheses have been in the market for a long time, but the PFC-Sigma Rotating Platform (RP) prosthesis (DePuy Orthopaedics, Inc, Warsaw, Ind) has been introduced in the market since 2000. Since, little is known about the in vivo kinematics of MB prostheses especially with cruciate retaining (CR). The objective of this study is to investigate the in vivo kinematics of MB RP-CR total knee arthroplasty during weight-bearing deep knee bending motion.
Patients and methods
We investigated the in vivo knee kinematics of 20 knees (17 patients) implanted with PFC-Sigma RP-CR. All TKAs were judged clinically successful (Hospital for Special Surgery scores >90), with no ligamentous laxity or pain. Mean patient age at the time of operation was 78.0 ± 6.0 years. Mean period between operation and surveillance was 15.0 ± 9.0 months. Under fluoroscopic surveillance, each patient did a wight-bearing deep knee bending motion. Femorotibial motion was analyzed using 2D/3D registration technique, which uses computer-assisted design (CAD) models to reproduce the spatial position of the femoral, tibial components from single-view fluoroscopic images. We evaluated the range of motion, axial rotation, and antero-posterior (AP) translation of the nearest point between the femoral and tibial component.
Results
Between the femoral and tibial components, the mean minimum flexion angle was on average 2.1±5.5 °. The mean maximum flexion angle was 118.0±9.9 °. The average range of motion was 115.8±12.8°. The femoral component relative to the tibial component demonstrated 5.5±3.7° external rotation for 0–120 degrees flexion. At full extension, the medial nearest point was −2.4±2.7 mm, and the lateral nearest point was −8.4±3.4 mm. The medial nearest point moved 1.3 mm anteriorly from full extension to 90° of knee flexion, and then moved 1.5mm posteriorly until maximum flexion. On the other hand, the lateral nearest point moved 0.4mm posteriorly from full extension to 90° of knee flexion, and then moved 3.6mm posteriorly until maximum flexion. At maximum flexion, the medial nearest point moved posteriorly to a final position of −2.6±3.3 mm and the lateral nearest point moved posteriorly to a final position of −12.5±3.6 mm [Fig.1]. From the results of bilateral contact positions at each flexion angle, patterns of kinematic pathways were determined. The kinematic pathway pattern was externally rotated due to a central pivot pattern from extension to 90° knee flexion. Subsequently from 90 to 120°, bilateral condyles moved backward.
Discussion and conclusion
In this study, we have evaluated the in vivo kinematics of MB prostheses with cruciate retaining motion during deep knee bending motion under weight-bearing condition. The results in this study demonstrated that the kinematic pathway pattern was externally rotated due to a central pivot pattern from extension to 90° knee flexion. Subsequently from 90 to 120°, bilateral condyles moved backward. This indicated that PCL functions.
