Kinematic difference between various geometric centers and contact points for tri-condylar bi-surface knee system

Area of Science:

• Orthopedic surgery
• Biomechanical engineering
• Medical device analysis

Background:

• Accurate assessment of in vivo knee kinematics is crucial for evaluating total knee arthroplasty (TKA) performance.
• Multi-radii femoral components are designed to mimic natural knee motion but require precise kinematic analysis.
• Distinguishing between different analytical points, such as contact points (CPs) and lowest points (LPs), is essential for reliable kinematic evaluation.

Purpose of the Study:

• To analyze and compare the motion of contact points (CPs), lowest points (LPs), and component facet centers in tri-condylar knee implants.
• To evaluate the accuracy of different analytical points in representing in vivo knee kinematics during deep knee bending.
• To determine the most reliable method for assessing femoral component rotation and translation.

Main Methods:

• In vivo knee kinematics were assessed in 43 knees with multi-radii femoral components during deep knee bend activity.
• A model fitting approach was utilized to analyze the motion of CPs, LPs, and component facet centers.
• Component rotation was defined using the Grood and Suntay coordinate system.

Main Results:

• Lowest points (LPs) closely corresponded to the geometric centers of the femoral component.
• LP and geometric center angles accurately represented component rotation angles.
• Antero-posterior translation of CPs was significantly overestimated compared to LPs.
• CP angles showed significant deviations from other rotation angle measurements.

Conclusions:

• Lowest points (LPs) are a more reliable indicator for evaluating in vivo knee kinematics compared to contact points (CPs).
• Polyethylene congruity significantly influences the accuracy of contact point analysis.
• The findings suggest that LPs provide a more robust measure for assessing the kinematics of tri-condylar knee implants.