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Updated: Aug 5, 2026
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In Vitro Application of a Wireless Sensor in Flexion-Extension Gap Balance of Unicompartmental Knee Arthroplasty
Published on: May 5, 2023
Final intraoperative gaps commonly exceed resection-based reference gaps during sequential balancing in imageless
Yugo Morita1, Jonggu Shin1, Mohammed El-Hassan1
1Complex Joint Reconstruction Center, Adult Reconstruction and Joint Replacement Service Hospital for Special Surgery New York New York USA.
Journal of Experimental Orthopaedics
|July 28, 2026
Summary
In robot-assisted total knee arthroplasty (RA-TKA), final joint gaps often exceeded reference measurements. Smaller initial gaps and increased laxity were linked to larger differences, highlighting the need for careful gap assessment.
Area of Science:
- Orthopedic Surgery
- Biomechanical Engineering
- Robotics in Medicine
Background:
- Total knee arthroplasty (TKA) aims to restore joint function and stability.
- Accurate intraoperative gap balancing is crucial for optimal TKA outcomes.
- Robot-assisted TKA (RA-TKA) offers potential for improved precision in surgical procedures.
Purpose of the Study:
- To quantify the difference between final and reference joint gaps in medial and lateral compartments during passive, imageless RA-TKA.
- To identify preoperative radiographic and intraoperative factors associated with variations in joint gap measurements.
Main Methods:
- Analysis of 379 primary TKA cases using a passive, imageless RA-TKA system.
- Measurement of medial and lateral compartment spaces in extension and 90° flexion.
- Definition of reference gaps based on initial measurements, bone resections, and implant components.
- Multivariable linear regression models adjusted for patient and implant factors.
Main Results:
- Final joint gaps consistently exceeded reference gaps in all measured conditions (extension and flexion).
- Mean final-minus-reference gap differences were 4.7mm medially and 3.4mm laterally in extension, and 4.2mm medially and 3.2mm laterally in flexion.
- Smaller initial compartment gaps, greater varus-valgus laxity, posterior-stabilized design, valgus alignment, and lateral osteophyte burden were associated with larger gap differences.
Conclusions:
- Passive, imageless RA-TKA frequently results in final joint gaps larger than reference measurements.
- Preoperative joint tightness and coronal laxity are significant predictors of gap variability.
- Surgeons should consider compartment-specific tightness and coronal laxity when interpreting resection-based gap estimates in RA-TKA.