Analysis of posterolateral and anterolateral laxity in varus knees undergoing robotic assisted total knee arthroplasty.

Achieving equal/ near equal gaps on medial and lateral side in flexion and extension is important for a well-balanced total knee arthroplasty (TKA). Assistive technologies like robotic assisted TKA (RATKA), permit intraoperative assessment of the lateral and medial gaps throughout the range of motion. Aim of study is to analyze the difference between the lateral and medial gaps in full extension and in full flexion in varus knees. A retrospective analysis of the prospectively collected data of the consecutive first 50 RATKA patients using Velys (with 1.9.4 software) system. Inclusion criteria were patients with advanced arthritis of the knee with varus deformity. Patients having inflammatory arthritis and valgus deformity were excluded from the study. An independent observer captured and analyzed the gaps on medial and lateral side in full extension, 90° of flexion and full flexion. Gaps were recorded on the accubalance graph after the upper tibial resection and insertion of the spring tensor instrument. Excessive laxity on the posterolateral side was balanced by externally rotating the femur implant (up to 7 degrees) to achieve balanced lateral and medial gaps in flexion. Difference between the lateral and medial side in full extension was 2.64 ± 0.72 mm. Difference between the posterolateral and posteromedial side in full flexion was 4.66 ± 1.06 mm. This difference in full flexion versus extension is statistically significant p -value < 0.0001. The study shows difference between lateral and medial gaps is more in flexion than extension in varus deformity of knee. This information is useful in determining femur implant rotation intraoperatively.