Optimization of sagittal and coronal planes with robotic-assisted unicompartmental knee arthroplasty

One of the anatomic goals of total knee arthroplasty (TKA) is optimizing in the coronal and sagittal plane. Accurate alignments of both planes have been correlated to functional outcome and range of motion. There is a paucity of evidence on the accuracy of unicompartmental knee arthroplasty (UKA) in balancing biplanar knee alignment – specifically sagittal plane alignment. Because robotic assisted UKA has an advantage of more accurately manipulating sagittal plane for optimal alignment and kinematics based on pre-operative and intraoperative CT planning we assessed the accuracy.

We reviewed the clinical and radiographic information of 94 robotic assisted UKA surgeries for balancing of sagittal and coronal knee anatomy using radiographic parameters, such as posterior condylar offset ratio (PCOR), posterior tibial slope (PTS), femoral-tibial angle, and joint line.

In the sagittal plane, we found no significant difference between pre and postoperative PCOR values. As planned, PTS was significantly lower after UKA compared to the native knee (4.91° vs 2.28°; p < 0.0001). In the coronal plane, there was no significant difference in the joint line however pre and post-operative mechanical axis were significantly different (5.43°± 2.58 of varus vs. 2.76°± 2.14 of varus; p < 0.0001).

This study attempts to quantify sagittal and coronal plane alignment after robotic assisted UKA. More attention should be paid to the role of sagittal plane alignment after UKA. We believe modifying posterior tibial slope, while maintaining PCOR is fundamental in achieving native kinematics and optimizing range of motion in the sagittal plane. This may be best-accomplished using robotic techniques for UKA.