The study is designed as a monocentric, prospective, observational, comparative follow-up study based on two previously treated patient groups. The first group consists of patients treated with the patient-specific unicondylar knee implant iUni®. For that group, 30 patients will be included in the study and analyzed. The final follow-up after 24 months has already been documented by the study center. Compared to that, a consecutive series of 50 Univation® X patients will be invited for a 24 months follow-up in 2018. In total, it is planned to include 80 retrospective patients for that historical control study design.