Femoral component rotational alignment in robotic-assisted total knee arthroplasty with functional knee positioning varies across knee phenotypes without affecting clinical outcomes

Purpose: This retrospective, observational study aimed to investigate the distribution of femoral component rotational alignment among different knee phenotypes and assess the clinical relevance of femoral component rotation variability in patients undergoing image-based robotic-assisted total knee arthroplasty (RA-TKA) performed with functional knee positioning (FP). It was hypothesized that femoral component rotational alignment can change based on preoperative knee phenotypes, without affecting clinical outcomes. Methods: A total of 256 patients who underwent image-based RA-TKA with the Mako robotic system at a single centre from February 2020 to March 2022 were included. Preoperative robotic-derived computed tomography (CT) data were gathered to determine the Coronal Plane Alignment of the Knee (CPAK) classification and the axial orientation of the distal femur. Intraoperative data relative to femoral component rotational alignment were collected. At a minimum of 24 months post-operatively, patients were administered the Forgotten Joint Score-12 (FJS-12) and the Knee Injury and Osteoarthritis Outcome Score for Joint Replacement (KOOS-JR). The distribution of femoral component rotation among phenotypes, as well as the relationships between alignment parameters and clinical outcomes, were assessed by means of linear regression models and one-way analysis of variance. Results: A total of 219 cruciate retaining TKAs were considered for implant positioning assessment. Femoral component rotational alignment varied significantly among different knee phenotypes, ranging from −6.9° internal to 6.6° external rotation with respect to surgical transepicondylar axis. No significant association was found between femoral component rotation and patient-reported outcomes (FJS-12 and KOOS-JR). Three patients (1.4%) underwent RA-TKA revision, while no patello-femoral complications were reported in any of the patients. Conclusions: In the setting of image-based RA-TKA performed with FP, the rotational alignment of the femoral component changes significantly among different knee phenotypes. These variations do not affect clinical outcomes at a minimum of 2 years of follow-up and do not result in significant patello-femoral complications. Level of Evidence: Level III.