Discrepancy between predicted and actual soft tissue balance in robot-assisted total knee arthroplasty

Achieving optimal soft tissue balance in total knee arthroplasty (TKA) is vital for successful clinical outcomes. Robotic-assisted TKA predicts postoperative soft tissue balance based on preoperative varus-valgus stress. Nevertheless, these predictions may not always be accurate due to changes in soft tissue balance after osteotomy and variability in manual stress application. Therefore, this study was conducted to investigate the differences between predicted and final soft tissue balance and determine the factors affecting these differences.

In 112 robotic-assisted TKA cases, the predicted joint gaps at extension (10°) and flexion (90°) were evaluated intraoperatively before osteotomy, and the final joint gaps were evaluated after final implantation under manual varus-valgus stress. Differences between the predicted and final gaps (DPFG) e calculated, and correlations between DPFG and preoperative parameters were analyzed.

The final joint gaps were significantly larger than the predicted gaps in both extension and flexion (P < 0.001). A greater preoperative hip-knee-ankle angle and increased flexion angle were associated with smaller DPFG in the medial compartment. Conversely, severe preoperative flexion contracture correlated with larger DPFG in extension in the lateral compartment.

Soft tissue balance predictions in robotic-assisted TKA are not always accurate, with the final joint gaps tending to be larger than predicted. Preoperative limb alignment and knee range of motion influence these differences, emphasizing the need for surgeons to interpret robotic predictions cautiously. Adjustments during surgery may be required to optimize soft tissue balance.