Changes In Tibial Insert Design Can Alter Knee Kinematics And Tibiofemoral Stress Distributions In Total Knee Arthroplasty

Changes In Tibial Insert Design Can Alter Knee Kinematics And Tibiofemoral Stress Distributions In Total Knee Arthroplasty

Shinichi Kuriyama, MD, PhD, JAPAN Sayako Sakai, MD, JAPAN Yugo Morita, MD, PhD, JAPAN Kohei Nishitani, MD, PhD, JAPAN Shinichiro Nakamura, MD, PhD, JAPAN Shuichi Matsuda, MD, PhD, JAPAN

Kyoto University, Kyoto, Kyoto, JAPAN


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Anatomic Location

Anatomic Structure

Diagnosis / Condition

Patient Populations

Diagnosis Method

Sports Medicine

Ligaments

PCL


Summary: Even with the same total knee arthroplasty design concept, different tibial inserts produced different knee kinematics and stress distribution results.


Introduction

About 20% of patients remain unsatisfied even after modern total knee arthroplasty. However, despite new tibial insert designs that aim to improve patient satisfaction, it is uncertain whether the expected effects are achieved. In addition, few studies have demonstrated differences in clinical outcome between different implant design. The purpose of this study was to develop a musculoskeletal computer simulation to simultaneously investigate knee kinematics and stress distribution in post-TKA models.

Methods

A musculoskeletal computer simulation using computed tomography data of a volunteer was developed to analyze knee biomechanics during squat (0°–120°). We compared biomechanical changes between posterior cruciate ligament (PCL)-retaining (CR)-TKA and CR-TKA without anterolateral (AL)-PCL, because the AL-PCL can be damaged during tibial bone resection. If the PCL were damaged intraoperatively, the surgeon would use a cruciate-sacrificing (CS) tibial insert with high anterior lip or PCL-substituting (PS) components with a post-cam mechanism. The femoral components had a single radius of curvature design. The AP movement of the medial and lateral femoral condyles against the tibial insert and peak equivalent stresses on the tibial insert were measured.

Results

The CR model showed little femoral anterior movement during mid-flexion, and then suitable medial pivot motion and roll-back of the femoral component. The CR model without the AL-PCL showed relatively larger femoral anterior movement than the CR model with an intact PCL, and also had attenuated medial pivot motion and roll-back. In the CS model, the femoral component moved anteriorly until the high anterior lip of the tibial insert exerted an effect, and it then rolled back. The PS model exhibited the same type of anterior femoral movement as the CS model during mid-flexion. However, the PS femoral component was forcibly rolled back when the post-cam mechanism was active at knee flexion of 60° or more. Regarding to equivalent stresses on the tibial insert, the PS model due to its post-cam mechanism exhibited higher equivalent stress on the tibial insert throughout squat than the other TKA models. In the CR model, the TF contact stress increased at mid-flexion because increased PCL tension caused femoral roll-back. The TF contact stress in the CS model increased significantly during deep knee flexion.

Discussion

This study using a musculoskeletal computer simulation revealed that simply by changing the type of tibial insert can alter not only knee kinematics, but also stress distribution, even with the same femoral component design in the same knee. The CR design showed good knee kinematics with little paradoxical femoral anterior movement. However, CR-TKA with partial PCL damage caused femoral anterior movement during mid-flexion. After PCL dysfunction, switching to a CS tibial insert with a high anterior lip could not reduce the mid-flexion instability. In contrast, the change to the PS components resulted in mechanical femoral roll-back against the tibia, but also increased stress distribution on the tibial polyethylene. Even with the same TKA design concept, different models produced different biomechanical results. There is a close relationship between knee kinematics and stress distribution after TKA.