Kinematical-aligning of femoral component decreases overstuffing of lateral distal condyle and provides better patellar tracking and postoperative outcomes in robotic-assisted total knee arthroplasty.

Patient-specific alignment philosophy in robot-assisted total knee arthroplasty (RA-TKA) is increasingly adopted, yet diverse strategies for achieving coronal-gap balancing persist. We aimed to compare clinical, radiographic, and intraoperative outcomes between two strategies during RA-TKA: femoral mechanical alignment (FMA) and femoral kinematic alignment (FKA). Clinical and radiographic data from 229 patients who underwent RA-TKA with cruciate-retaining implants were retrospectively analysed. Patients were allocated to either the FMA group (mechanical alignment of the femoral side) or the FKA group (kinematic alignment of the femoral side). Although the MAKO system recorded resection angles and thicknesses, calliper measurements were performed on the medial and lateral distal condyles, posterior condyles, and tibia, and resection-implant differences were calculated. The rate of extensive lateral retinacular release (LRR) was recorded. Radiographic measurements and patient-reported outcome measures were collected preoperatively and at 1 year postoperatively. The mechanical lateral distal femoral angle (mLDFA), and mechanical medial proximal tibial angle were measured on full-length standing radiographs. Patellar tilt (PT) and lateral patellar angle were measured on 30° patellar axial radiographs. The FMA group demonstrated greater varus orientation of the femoral component, resulting in significantly decreased lateral distal condyle dimensions and larger bone-implant discrepancies at the lateral femoral condyle compared with the FKA group, especially in patients with smaller LDFAs. The FMA group also showed a significantly higher rate of LRR and an increased PT in patients who did not underwent LRR, with higher postoperative WOMAC and lower Feller scores. The FKA strategy reduces lateral femoral condyle overstuffing, improves patellar tracking and postoperative outcomes. These findings suggest that an accurately surfaced distal femur is important during TKA.