Getting REAL balance: a simple and reproducible method for imageless robotic TKA

In imageless robotic-assisted total knee arthroplasty (RA-TKA), intraoperative assessment of ligament balance may be influenced by asymmetric cartilage wear, potentially misrepresenting true soft-tissue behavior. Functional alignment (FA) aims to restore constitutional alignment while respecting the native ligament envelope. Using the unworn compartment as the primary reference for intraoperative balancing may reduce the effect of asymmetric wear and improve mediolateral symmetry.

A retrospective analysis was performed on 180 knees (176 patients) undergoing femur-first imageless RA-TKA with a functional alignment strategy at a single-volume center. All procedures were performed using the ROSA Knee System with a medial congruent implant. Intraoperative balancing prioritized the unworn or less affected compartment, targeting a 19-mm implant space with near-symmetric medial-lateral laxity in extension and flexion. Medial and lateral laxities were recorded robotically before implantation and after final component placement and classified using the Robotic Evaluation of Articular Laxity (REAL).

Preoperatively, lateral laxity exceeded medial laxity in both extension and flexion. Following implantation, mediolateral symmetry was restored with a significant reduction in medial-lateral laxity differences (p < 0.001). At final assessment, 178 knees (98.9%) were classified as REAL 1A. Soft-tissue releases were required in 14 knees (7.8%), with no intraoperative instability, additional bone recuts, or device-related complications.

In femur-first imageless RA-TKA performed according to functional alignment principles, unworn-compartment-based balancing enables reliable restoration of mediolateral ligament symmetry with balanced REAL phenotypes and a limited need for soft-tissue releases, representing a refinement of robotic ligament assessment in knees with asymmetric osteoarthritis during contemporary robotic surgery.