Posterior Condylar Offset and Joint-Line Restoration Are Associated with Improved Patient-Reported Outcomes After Robotic-Arm-Assisted Total Knee Arthroplasty.

Abstract

The relationship between sagittal alignment in total knee arthroplasty (TKA) and patient-reported outcomes remains incompletely defined. Prior studies have largely relied on conventional instrumentation and radiographic measurements, which are limited by variability between planned and executed component position and inability to precisely quantify intraoperative balance. Robotic-arm-assisted TKA enables highly reproducible execution, providing an opportunity to identify sagittal parameters that are measurable, actionable, and clinically meaningful. The purpose of this study was to determine which sagittal alignment parameters are associated with patient-reported outcomes. We performed a retrospective analysis of 479 consecutive robotic-arm-assisted TKAs. There were 12 sagittal alignment parameters extracted from intraoperative robotic planning data, including posterior tibial slope, femoral sagittal rotation, tibial sagittal rotation, change in posterior condylar offset (change in PCO), and change in tibial resection depth. Patient-reported outcomes were assessed using the Knee injury and Osteoarthritis Outcome Score for Joint Replacement (KOOS JR) and the Patient-Reported Outcomes Measurement Information System (PROMIS) at six weeks, three months, and one year. Associations were evaluated using univariate correlations and exhaustive multivariable regressions (1,585 predictor combinations per outcome) with ridge regression, five-fold cross-validation, and false discovery rate correction. At three months, lateral change in PCO correlated positively with KOOS JR improvement (r = 0.179, P = 0.036) and with PROMIS Pain Interference reduction (r = -0.218, P = 0.009). The highest-performing models consistently included medial and lateral change in PCO and change in tibial resection depth with positive cross-validated R² values. In robotic-arm-assisted TKA with a condylar-stabilizing implant, restoration of posterior condylar offset and preservation of joint-line position demonstrated consistent significant associations with improved function and reduced pain. These findings suggest sagittal optimization should prioritize PCO restoration and joint-line preservation to optimize patient-reported recovery.