Ligament Tension and Balance before and after Robotic-Assisted Total Knee Arthroplasty - Dynamic Changes with Increasing Applied Force.

The optimal force applied during ligament balancing in total knee arthroplasty (TKA) is not well understood. We quantified the effect of increasing distraction force on medial and lateral gaps throughout the range of knee motion, both prior to and after femoral resections in tibial-first gap-balancing TKA. Twenty-five consecutive knees in 21 patients underwent robotic-assisted TKA. The posterior cruciate ligament was resected, and the tibia was cut neutral to the mechanical axis. A digital ligament tensioning tool recorded gaps and applied equal mediolateral loads of 70 N (baseline), 90 N, and 110 N from 90 degrees to full extension. A gap-balancing algorithm planned the femoral implant position to achieve a balanced knee throughout flexion. After femoral resections, gap measurements were repeated under the same conditions. Paired t -tests identified gap differences between load levels, medial/lateral compartments, and flexion angle. Gaps increased from 0 to 20 degrees in flexion, then remain consistent through 90 degrees of flexion. Baseline medial gap was significantly smaller than lateral gap throughout flexion ( p <0.05). Increasing load had a larger effect on the lateral versus medial gaps ( p <0.05) and on flexion versus extension gaps. Increasing distraction force resulted in non-linear and asymmetric gap changes mediolaterally and from flexion to extension. Digital ligament tensioning devices can give better understanding of the relationship between joint distraction, ligament tension, and knee stiffness throughout the range of flexion. This can aid in informed surgical decision making and optimal soft tissue tensioning during TKA.
Competing Interests: A.K.S. declares that he has no conflict of interest. C.P., reports that he is an employee of Corin Group/Omni and that he holds stock options in Corin Group/Omni. S.S. reports that he is an employee of Corin Group/Omni. D.L. declares that he has no conflict of interest. J.M.V. reports receiving personal fees from Corin Group, Intellijoint Surgical, Medacta, and Zimmer, receiving payments as a consultant for Corin Group, Intellijoint Surgical, Medacta, and Zimmer, holding stock options in Intellijoint Surgical and Motion Insights, and receiving research funding from Corin Group. J.L. reports receiving consulting fees from Corin Group.
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