Image-free robotic-assisted total knee arthroplasty is associated with joint line distalization and improves mid-flexion instability: A prospective cohort study.

Purpose: Total knee arthroplasty (TKA) has demonstrated long-term durability, with a significant reduction in revisions due to polyethylene wear and component loosening. However, mid-flexion instability (MFI) is a key factor in early TKA revisions, affecting patient satisfaction and implant longevity. Recent advancements in robotic-assisted TKA (raTKA) provide precise joint line (JL) restoration and component positioning, potentially reducing MFI. This prospective study evaluated the impact of image-free raTKA on MFI and JL restoration. Methods: This prospective cohort study included 59 knees undergoing primary TKA using the image-free robotic systems NAVIO® and CORI® and the JOURNEY II® Bi-Cruciate Stabilized knee system. Intraoperative component gap (CG) measurements at 0°, 30°, 60° and 105° of flexion were taken, and JL changes were assessed pre- and post-operatively using computed tomography (CT)-based three-dimensional (3D) models with the 3D-3D matching technique. The distal femoral JL was quantified. Results: Both the medial and lateral CG at 30° and 60° were significantly smaller compared to those at 0° and 105°. Post-operative JL showed distalization of 1.5 mm at the medial femur and 2.0 mm at the lateral femur compared to preoperative JL. Conclusions: This study is the first to assess JL restoration in raTKA using CT-based bone landmarks, offering precise insights. Image-free raTKA facilitates precise JL restoration, optimizing knee kinematics and enhancing stability. These findings suggest that this technique contributes to improved post-operative joint function and greater patient satisfaction. Level of Evidence: Level II, prospective cohort study.