Rotational constraint of posterior-stabilized total knee prostheses

Area of Science:

• Orthopedic biomechanics
• Biomaterials science

Background:

• Posterior-stabilized knee implants are widely used.
• Understanding their rotational constraint is crucial for clinical outcomes.

Purpose of the Study:

• To compare the rotational constraint characteristics of four posterior-stabilized knee implants.
• To assess the influence of lubrication on implant torque generation.

Main Methods:

• Quantified rotational torques for Triathlon, NexGen, PFC, and Genesis II implants.
• Tested internal/external rotation up to +/-20 degrees at various flexion angles (hyperextension to 90 degrees).
• Compared torque in dry versus serum (lubricated) environments.

Main Results:

• Significantly higher torques were generated in dry conditions compared to serum.
• In extension, box-post interaction and insert anterior lip were key.
• In flexion, rollback and posterior lip geometry were critical.
• Triathlon demonstrated the least torque for +/-10 degrees rotation; PFC and Genesis II were most constrained.

Conclusions:

• Rotational constraint varies significantly among posterior-stabilized knee implant designs.
• Lubrication status (dry vs. serum) substantially affects measured torque.
• Implant design features, including rollback and lip geometry, dictate rotational stability at different flexion angles.