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® software (Stryker®, Mahwah, USA) intra-operatively.RESULTS: The lateral UKA had a mean internal tibial rotation of 15.4?±?3°, a mean external femoral rotation of 0.96?±?2.4°, and a mean tibial slope of 4.7?±?1.3°. The medial UKA had a mean internal tibial rotation of 0.18?±?2.7°, a mean internal femoral rotation of 0.35?±?2.2°, and a mean tibial slope of 5.4?±?1.3°. The tibial rotations, femoral valgus, tibial varus and tibial size significantly differed between medial and lateral UKA (p?