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Published on: May 5, 2023
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Balancing mobile-bearing unicondylar knee arthroplasty in vitro
Thomas J Heyse1, Joshua Slane2, Geert Peersman2,3
1Center of Orthopedics and Trauma Surgery, University Hospital Marburg, Baldingerstrasse, 35043, Marburg, Germany. heyse@med.uni-marburg.de.
Summary
Properly balancing mobile-bearing unicondylar knee arthroplasty (UKA) is crucial. Over-stuffing the medial compartment leads to significant kinematic changes and increased superficial medial collateral ligament (sMCL) strain, highlighting the importance of optimal implant balancing.
Area of Science:
- Orthopedic Surgery
- Biomechanics
- Biomedical Engineering
Background:
- Mobile-bearing unicondylar knee arthroplasty (UKA) requires precise balancing for optimal outcomes.
- Improper balancing can lead to complications such as pain, loosening, and osteoarthritis progression.
Purpose of the Study:
- To investigate the effects of improper balancing, specifically over-stuffing and under-stuffing, on knee kinematics and joint contact stress in MB UKA.
- To hypothesize that over-stuffing would result in increased valgus alignment and higher lateral contact forces.
Main Methods:
- Seven fresh-frozen cadaver knees underwent kinematic testing in native state and after medial MB UKA implantation.
- Motion patterns included passive flexion-extension, open chain extension, and squatting.
- Inlay thickness was varied to simulate optimal, under-stuffed, and over-stuffed medial compartments, with kinematic data and ligament strains analyzed.
Main Results:
- Under-stuffing yielded kinematics closest to the native knee.
- Over-stuffed and optimally balanced knees exhibited increased valgus alignment.
- Superficial medial collateral ligament (sMCL) strain significantly increased after UKA, irrespective of inlay thickness, particularly in mid-flexion.
Conclusions:
- Optimal balancing is critical in MB UKA to minimize kinematic deviations from the native knee.
- Over-stuffing should be avoided due to significant kinematic alterations and elevated sMCL strain.
- Thinner inlays are advisable if stability and inlay retention are not compromised.
