Increased Femoral Component Flexion and No Difference in Slope in Robotic- versus Computer-Assisted Total Knee Arthroplasty When Targeting Mechanical Alignment.

Abstract

Robotic-assisted surgery (RAS) in total knee arthroplasty (TKA) is becoming popular due to better precision, when compared with other instrumentation. Although RAS has been validated in comparison with computer-assisted surgery (CAS), data from clinical settings comparing these two techniques are lacking. This is especially the case for sagittal alignment. Whereas pure mechanical alignment (MA) aims for 0 to 3 degrees of flexion of the femoral component and 3° of posterior slope for the tibial component, adjusted MA (aMA) mostly used with RAS allows for flexing of the femoral component for downsizing and increase of slope for an increase of the flexion gap. In the present study, we compared sagittal alignment after TKA using RAS with aMA and CAS targeting MA, which has been the standard in the center for more than 10 years. We analyzed a prospectively collected database of patients undergoing TKA in a single center. Femoral component flexion and tibial slope were compared for both techniques. In 140 patients, 68 CAS and 72 RAS, we found no difference in tibial slope (p = 0.661), 1° median femoral component flexion (p = 0.023), and no difference in outliers (femur, p = 0.276, tibia, p = 0.289). RAS slightly increases femoral component flexion, but has no influence on tibial slope, when compared with CAS in TKA. If MA is the target, RAS provides no benefit over CAS for achieving the targeted sagittal alignment. LEVEL OF EVIDENCE: Level III retrospective study.