Image-based robotic unicompartmental knee arthroplasty allowed to match the rotation of the tibial implant with the native kinematic knee alignment

Purpose Image-based robotic tools improve the accuracy of unicompartmental knee arthroplasty (UKA) positioning, but few studies have examined its effect on axial alignment. The aim of this study was to compare the characteristics of tibial and femoral implant positioning, mainly the tibial rotation, during medial or lateral UKA, performed with an image-based robotic assisted system. Methods A total of 71 UKA performed between September 2021 and June 2022 (53 medial and 18 lateral) were analyzed. All data regarding implant positioning (rotation, coronal and sagittal alignment) for tibial and femoral components were obtained using MAKO (R) software (Stryker (R), Mahwah, USA) intra-operatively. Results The lateral UKA had a mean internal tibial rotation of 15.4 +/- 3 degrees, a mean external femoral rotation of 0.96 +/- 2.4 degrees, and a mean tibial slope of 4.7 +/- 1.3 degrees. The medial UKA had a mean internal tibial rotation of 0.18 +/- 2.7 degrees, a mean internal femoral rotation of 0.35 +/- 2.2 degrees, and a mean tibial slope of 5.4 +/- 1.3 degrees. The tibial rotations, femoral valgus, tibial varus and tibial size significantly differed between medial and lateral UKA (p < 0.05). There was no significant difference in femoral rotation, flexion, femoral size, slope, and polyethylene thickness between medial and lateral UKA. Conclusion Medial and lateral UKA had significantly different implantation characteristics related to the biomechanics of the knee compartments. Image-based robotic UKA allowed precise femorotibial positioning per-operatively to match native kinematic alignment.