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- Constant Friction Knee:
    - simply a hinge that is designed to dampen knee swing via a screw or rubber pad that applies friction to the knee bolt;
    - it is a general utility knee, and may be used on uneven terrain;
    - it is the most common knee used in childhood prosthetics;
    - its major disadvantage, is that it allows only single speed walking & relies soley on alignment for stance phase stability and is therefore not 
           recommended for older, weaker patients;
           - because stability relies on stance alignment, the knee axis must be positioned posterior to the plumb line;

- Variable Friction (Cadence Control)
    - knee allows resistance to knee flexion to increase as the knee extends by employing a number of staggered friction pads;
    - this knee allows walking at different speeds, but is not durable and is not available in endoskeletal systmes;

- Polycentric (4 bar linkage)
    - has a variable instant center of rotation that provides for different stability characteristics during the gait cycle and may allow increased 
           flexion for sitting;
    - in extension, the center of rotation is posterior to the plumb line;
    - it is favored for pts w/ knee disarticulations and bilateral amputees

- Fluid Control (Hydraulic Knee)
    - allows adjustment of cadence response by changing resistance to knee flexion via a piston mechanism;
    - provides superior control in swing phase by using fluid hydraulics to vary the resistance according to the speed of gait;
    - stiffness can be adjusted for the specific needs of the patient;
    - design prevents excessive flexion and is extended earlier in the gait cycle, allowing a more fluid gait;
    - knee is best used in young active patients who prefer greater utility and variability at the expense of more weight