Bi-unicondylar knee replacement laxity with changes to simulated soft tissue constraints

Area of Science:

• Orthopedic Surgery
• Biomechanical Engineering
• Biomaterials Science

Background:

• Unicondylar knee replacement (UKR) offers a less invasive alternative to total knee replacement.
• Optimal ligament balancing and knee laxity are critical for UKR performance and implant survival.
• Current knee simulator protocols may not fully represent in vivo conditions.

Purpose of the Study:

• To investigate the impact of simulated anterior cruciate ligament (ACL) and posterior cruciate ligament (PCL) laxity on UKR contact kinematics.
• To compare kinematics under varied laxity conditions with standard knee simulator protocols.
• To inform the design of UKR systems more resilient to soft tissue variations.

Main Methods:

• Utilized force-controlled ISO-14243-1 knee testing simulation for medial and lateral UKR implants.
• Employed flat and symmetric ultrahigh-molecular-weight polyethylene inserts.
• Developed a novel method to capture tibiofemoral contact path kinematics (anteroposterior and mediolateral).

Main Results:

• Statistically significant differences in knee kinematics were observed under various soft tissue configurations compared to standard protocols.
• Anteroposterior and mediolateral movements varied notably with simulated ligament laxity.
• The study identified deviations from accepted 'standard' knee simulator outputs.

Conclusions:

• Simulated ligament laxity significantly alters UKR kinematics, deviating from standard wear testing results.
• These findings highlight the need to consider soft tissue conditions in UKR design.
• Potential for UKR design enhancements to address varying soft tissue deficiencies and improve outcomes.