Four-Bar Polycentric Knee
The four-bar polycentric knee is the next knee described as "inherently stable." The stability of this
knee is in its design in that the alignment within the knee creates stability and the alignment of the
knee within the total alignment of the prosthesis is stable, therefore providing security and stability
while providing ease of swing into flexion from an extended position. The advantage of this knee is
that it will bend with weight-bearing through the forefoot or toe and will lock with the swing phase
for security when placing weight through the heel. Given the design of the knee, the prosthesis in
flexion during the initial and the mid-swing phase will shorten the shank making it an ideal knee for
those with a knee disarticulation when attempting to keep the knee center close to the same height
as the sound limb. The disadvantage is the potential for maintenance on the knee; given the number
of hinges and articulations and the potential for the wearer to create a gait cycle with a "goosestepping" tendency: kicking the knee out hard and fast and slamming the heel of the foot down for
security going in to stance phase.