The Knee

    The knee unit is probably the most complex component. There are several types of knee units. The best knee units have hydraulics in them. One purpose of the hydraulics is so that as the amputee is walking, the lower leg does not swing back too far. If the knee was just a "swinging gate", then as the amputee would start walking, the lower leg would tend to swing backwards at first and the amputee would have to wait for it to come forward to make a step. The hydraulic action gives the amputee a kind of control of the lower portion of the leg.  Remember, the knee that God gave you is gone, and so is the control of the lower portion of you leg. Hydraulics will tend to stiffen the lower portion of the leg so that it "comes out" with the upper part of the leg (controlled by your socket). The hydraulic systems are adjustable. Generally the stronger of a walker you are, the more resistance you need. The other side of the adjustment is for when the lower leg starts moving forward. During this "extension phase", if your leg has no hydraulics, it can "bang" rather fast into the extended position. The hydraulics have adjustment that allows the extension to be cushioned as it extends fully. Generally almost any age amputee can benefit from a hydraulic knee unless there are special circumstances noted by your prosthetist. So, make sure that you get a hydraulic knee, anything else is lesser technology.

    Many of the hydraulic knees are "single axis" knees. There are also some "multi-axis" hydraulic knees out there. These knees are supposed to better mimic the action a god-given leg makes. These knees can also work out real well for the above knee amputee.