Aim: The LPS Mobile Flex was designed to adress a physiological range of motion after TKA. Methods: We compared 40 LPS and 40 LPS Flex knees in a prospective randomized study. The average age was 64.9 (60–70) years in the LPS group (26 female/14 male) and 63.6 (54–70) years in the LPS Mobile Flex group (27 female/14 male. The surgeries were performed by two surgeons. Same approaches and techniques were used to adress the ßexion capacities. No patient was lost to the follow up. The outcome was clinical and radiological investigated and comprised after 3 month. For the clinical comparison the American knee society score was used. Results: The average range of motion in the LPS group was 110û (90–150û) after 3 month (preop. ßexion was 111û (85–140û). At the same time the average range of motion in the LPS Flex group was 125û (95–150) (preop. ßexion was 108û (80–130). After 3 month the ßexion ability was signiþcantly improved by 15û using the LPS ßex. According the knee score there were no significant differences between the groups besides the range of motion. Also radiologically there were no differences between the groups. 92,5% of the patients in each group showed central tracking in the patellofemoral groove in the sunrise view. Conclusions: The LPS Mobile Flex is an alternative to improve knee function and make the knee more physiological after TKA. To take advantage of the design features it requires a proper surgical technique and a proper patient selection.