Proximal Tibial Resection Alone Leads to a Significant Increase in Flexion Gap Size in Tibia-First Robotic-Assisted Posterior-Stabilized Total Knee Arthroplasty.

Background: Alignment philosophies in total knee arthroplasty (TKA) have shifted from universal mechanical alignment to patient-specific strategies aiming to optimize soft-tissue balance and improve satisfaction. Robotic-assisted TKAs have enhanced preoperative planning and intraoperative assessments, but the effects of sequential bone cuts on joint gaps remain unclear. This study evaluates whether flexion and extension gaps change after the tibial resection in tibia-first (TF) robotic-assisted posterior-stabilized (PS) TKA. Methods: A prospective observational study included 82 knees (78 patients) undergoing robotic-assisted TKA with a TF workflow. Gap assessments were recorded pre- and post-proximal tibial bone resection, both after posterior cruciate ligament (PCL) excision, using the Velys robotic system software. Changes in medial and lateral flexion and extension gaps were analyzed as paired measurements and correlated with femoral component modifications. Results: Removal of the proximal tibial bone cut in isolation led to significant changes in the measured gaps, disproportionately more for the flexion than extension space. Medial and lateral flexion gaps increased by a mean of 2.57 mm and 2.30 mm, respectively, compared to minor changes in mean extension gaps (0.26 mm medially and -0.31 mm laterally) ( Conclusions: Proximal tibial bone resection, independent of PCL excision, significantly affects flexion gap size in PS-TKA, often necessitating intraoperative adjustments to femoral component size and position. The TF approach allows surgeons a second chance to optimize ligament balance through femoral component positioning, to achieve their desired balance target. While the clinical benefits of this intraoperative flexibility are intuitive, further research is warranted to establish whether this improves patient clinical outcome and satisfaction.