The Impact of Femoral Component Rotation on Patellar Position and Functional Outcomes in Total Knee Arthroplasty.

Abstract

Patellar malalignment may occur after total knee arthroplasty (TKA) and can lead to pain and dysfunction. The purpose of this study was to examine the relationship between femoral component rotation and patellar position in TKA. This was a retrospective, multicenter study of patients who underwent conventional or robotic-assisted TKA. In conventional cases, femoral rotation was set to 3° of external rotation relative to the posterior condylar axis; in robotic cases, femoral component rotation was planned to create balanced flexion gaps and defined relative to the posterior condylar axis. Preoperative and postoperative radiographs were analyzed to determine patellar translation, tilt, and coronal limb alignment. Knee injury and Osteoarthritis Outcome Score-Joint Replacement, range of motion (ROM), and postoperative forgotten joint scores (FJS) were collected. Cases were analyzed in incremental groups stratified by femoral component rotation, ranging from greater than 6° of external rotation to greater than 0 to 3° of internal rotation. Postoperative patellar translation and tilt were significantly different across all femoral rotation groups (P = 0.002, P = 0.005). Compared to all other femoral rotation groups, lateral patellar translation was reduced when femoral components were internally rotated between 0 and 3°. Conversely, those with femoral component internal or external rotation between 0 and 3° had the most postoperative patellar tilt on sunrise radiographs. Postoperative FJS, improvement in Knee injury and Osteoarthritis Outcome Score-Joint Replacement and ROM, and the proportion of patients who met the minimal clinically important difference were significantly better in patients whose femoral components were between 0 and 3° of internal rotation. However, pairwise comparisons with patients who had component external rotation between 0 and 3° demonstrated statistically similar results. Internal and external rotation of the femoral component of up to 3° decreases the likelihood of patellar translation, results in improved functional outcomes and ROM, and leads to improved FJS.