Comparison of joint laxity measured using 60- and 80-N distraction forces and manual stress during robot-assisted total knee arthroplasty

Abstract Background Appropriate intraoperative soft-tissue balance is essential for achieving successful outcomes following total knee arthroplasty (TKA). However, the optimal distraction force for evaluating joint laxity remains unclear. This study aimed to compare joint laxities measured using specific distraction forces with those obtained under manual varus–valgus stress and assess the interobserver variability. Methods A total of 55 bi-cruciate-stabilized TKAs were performed using a robotic system. Medial and lateral joint laxities were evaluated using a force-controlled tensioner device under a distraction force of 60 and 80 N at 10°, 30°, 60°, and 90° of flexion and under manual varus–valgus stress using the robotic system. To determine interobserver differences, measurements were conducted by two surgeons Results In the medial compartment, joint laxity under manual stress was comparable to that measured using a distraction force of 80 N at 10° and 30° of flexion and a distraction force of 60 N at 60° and 90° of flexion. In the lateral compartment, joint laxity under manual stress was similar to that measured using a distraction force of 80 N across at 10° and 90° of flexion. Interobserver variability was greater in the lateral compartment than in the medial compartment, especially at higher flexion angles. Conclusions Manual stress evaluation corresponded to different distraction forces depending on the compartment and flexion angle. The lateral compartment showed greater measurement variability, suggesting the need for careful assessment and standardization of intraoperative joint laxity evaluation during robot-assisted TKA.