.pneumatic knee joint VS Hydraulic knee joint

Both air pressure and hydraulic pressure are known as the use of fluid mechanics to control joints, which provide variable resistance, allowing patients to walk comfortably at different speeds.

These devices consist of pistons in cylinders, including air or liquid. When the knee is bent, compressed air stores energy, which is then released when the knee joint is extended. Gait control is further enhanced by adding spring coils. Pneumatic joints can generally provide excellent swing control performance, but the efficiency is lower than that of hydraulics.

For active amputees, hydraulic joints can provide the closest function to a normal knee joint. The hydraulic system uses a liquid medium (usually silicone oil) instead of air to respond to various travel speeds. Although hydraulic knee joints provide a smoother gait, they are heavier and require more maintenance, and the assembly cost is very high.