Mechanism of polycentric knee units By -: Sibasis pattanayak

How polycentric knee joint provides positive stability?

 

As human anatomical knee joint, polycentric knee has moving centre of rotation.It moves around more than one axis through a four bar or more bar linkage system.

What defines knee stability in polycentric knee joint?

A proximal and posterior location of ICOR(Instantaneous centre of rotation) enhances the stability of knee during stance phase of the gait.

During swing phase as the knee unit flexes the four bar polycentric axis of motion leads to relative "shortening"of the shin & foot components which helps in toe clearance during swing phase.

Polycentric knee joint is more suitable for shorter residual limbs.

INDICATIONS:-WEAK HIP EXTENSORS

The stability characteristics of any prosthetic

knee can be described by the relationship

between four factors:

—the muscular hip moment

—the load line

—the instantaneous centre of thigh-shank

rotation

—the brake moment generated by the knee

mechanism