Postoperative Knee Flexion Angle Is Affected by Lateral Laxity in Cruciate-Retaining Total Knee Arthroplasty

Background: Although many studies have reported that postoperative knee flexion is influenced by preoperative conditions, the factors which affect postoperative knee flexion have not been fully elucidated. We tried to investigate the influence of intraoperative soft tissue balance on postoperative knee flexion angle after catciate-retaining (CR) total knee arthroplasty (TKA) using a navigation and an offset-type tensor. Methods: We retrospectively analyzed 55 patients with osteoarthritis who underwent TKA using emotion-CR (B. Braun Aesculap, Germany) whose knee flexion angle could be measured at 2 years after operation. The exclusion criteria included valgus deformity, severe bony defect, infection, and bilateral TKA. intraoperative yaws ligament balance and joint component gap were measured with the navigation (Orthopilot 4.2; B. Braun Aesculap) while applying 40-lb joint distraction force at 0 degrees to 120 degrees of knee flexion using an offset-type tensor. Correlations between the soft tissue parameters and postoperative knee flexion angle were analyzed using simple linear regression models. Results: Varus ligament balance at 90 degrees of flexion (R = 0.56; P < .001) and lateral compartment gap at 90 degrees of flexion (R 0.51; P < .001) were positively correlated with postoperative knee flexion angle. In addition, as with past studies, joint component gap at 90 degrees of flexion (R 0.30; P <.05) and preoperative knee flexion angle (R = 0.63; P < .001) were correlated with postoperative knee flexion angle. Conclusion: Lateral laxity as well as joint component gap at 90" of flexion is one of the most important factors affecting postoperative knee flexion angle in CR-TKA.