Posterior-stabilized versus mid-level constraint polyethylene components in total knee arthroplasty

Area of Science:

• Orthopedic Surgery
• Biomechanics
• Biomedical Engineering

Background:

• Total knee arthroplasty (TKA) aims to restore knee function and stability.
• Mid-level constraint designs are developed to manage coronal plane laxity in TKA.
• Posterior-stabilized (PS) designs offer a different approach to knee stability.

Purpose of the Study:

• To compare the kinematics and ligament forces of mid-level and PS TKA designs.
• To evaluate stability in coronal, sagittal, and axial planes under simulated clinical loads.
• To assess the performance of Zimmer Biomet Persona PS and mid-level designs in a cadaver model.

Main Methods:

• TKA was performed on eight cadaveric knees using robotic manipulation.
• Both mid-level and PS designs were tested under varus/valgus moments, internal-external rotation moments, and anteroposterior forces.
• Tibiofemoral angulations, translations, and medial/lateral collateral ligament (MCL/LCL) forces were measured at multiple flexion angles.

Main Results:

• Mid-level inserts significantly reduced varus/valgus angulations and internal-external rotations across flexion angles (p ≤ 0.027).
• Anterior tibial translation was reduced by mid-level inserts only at 90° flexion (p = 0.036).
• Mid-level inserts decreased LCL forces under varus and internal rotation moments, and MCL forces under external rotation, but not MCL forces under valgus or anterior loads.

Conclusions:

• Mid-level TKA inserts effectively reduce coronal and axial plane laxities compared to PS inserts.
• The sagittal plane stabilization benefit of mid-level inserts was limited in this study.
• Both mid-level and PS designs rely on the MCL for resisting anterior loads during simulated clinical examination.