Osteophyte Bony Balancing in Robotic Total Knee Arthroplasty: A Surgical Technique and Predictive Algorithm for Soft Tissue Laxity

The removal of osteophytes during total knee arthroplasty (TKA) results in reduced soft tissue tension, which may result in joint laxity. Thus, for gap balancing, a surgeon may try to predict the effect of osteophyte removal on the resulting flexion and extension gap before any bone cuts are made and before those osteophytes are removed. Posterior osteophytes, however, are relatively inaccessible, since their removal can be done only after posterior bone cuts are made on the femur. Any laxity created by posterior osteophyte removal cannot be corrected by adjusting bone cuts because they have already been made. The authors have developed a predictive algorithm for use in robotic TKA, which anticipates the effect of osteophyte removal, allowing adjustment in bony resection before any bone cuts are made. The cross-sectional area of the posterior femoral osteophytes is measured on the sagittal plane of the preoperative computed axial tomography (CAT) scan. The authors' method of osteophyte correction is to make changes to the tibial cut based on the size and shape of the posterior osteophytes, as they believe the laxity created by osteophyte removal effects both extension and flexion. The amount and specific location of bony resection are then determined based on the size and location (posteromedial vs. posterolateral) of the osteophytes. Through the described technique, the authors have found that the amount of laxity created by osteophyte removal correlates directly to the dimension of the osteophyte over which the soft tissue extends. The size and shape of initially inaccessible posterior osteophytes, determined using CAT scan-based imaging, were used to create a predictive bony balancing algorithm, designed to be incorporated with the surgeon's preferred bony balancing technique. Our predictive algorithm anticipates the laxity created by osteophyte removal prior to their removal and can be used to alter bone resection parameters and/or implant parameters (e.g., thickness of a tibial liner) to accommodate the increased laxity, allowing for the conservation of bone and correction of deformity.