Introduction. The knee joint is the most important component of a transfemoral prosthesis. Traditional mechanical knees rely on fixed friction or simple hydraulic settings, which work well only at one walking speed. Microprocessor-controlled knees (MPKs) use sensors and a small computer to adjust knee resistance continuously during walking. How an MPK Works. Sensors measure knee angle, angular velocity, and the load on the prosthesis. The microprocessor analyses these signals many times per second to identify the phase of gait. It then commands a valve in a hydraulic or magnetorheological damper to increase resistance during stance, giving stability, or to reduce resistance during swing, allowing a smooth and natural step. Clinical Benefits. Studies have shown that MPK users experience fewer stumbles and falls, better walking on slopes and stairs, and more symmetrical gait compared with mechanical knees. The ability to adapt automatically to different speeds also reduces the mental effort required while walking, which is especially valuable for older or less active users. Limitations. MPKs are considerably more expensive than mechanical knees and require battery charging, regular maintenance, and trained clinicians for programming. They may also be sensitive to water and dust, which limits their use in some environments. Future Trends. Newer designs include powered knees with motors that can actively assist stair climbing and standing up, and intelligent control based on machine learning that recognizes the user's activity and adjusts settings automatically.