This recommendation is for a polycentric knee joint with an integrated extension assist mechanism suitable for trans-femoral amputees with moderate functional levels, including those with a maximum body weight of 100 kg and possibly hip disarticulating amputees. The knee joint provides medium stance and swing phase stability, with the upper and lower joint sections connected by linkage bars. The stance phase stability is achieved through polycentric kinematics, allowing for adjustment of the instant center of rotation via stop adjustment. The swing phase is controlled through step-less adjustment of axis friction and the extension assist spring.