medicine&technology 01.2019

■ [ TECHNOLOGY ]
Polymer Plain Bearings in
Knee, Lighter and Quieter
Plain bearings in the prosthesis | Plain bearings made of high-performance polymers
are self-lubricating and are lighter and quieter than bronze bearings. Thus, after extensive
testing, manufacturer of prosthetic knee joints, Otto Bock, decided to go with
the plastic solution.
Iglidur plain bearings
allow the available
space to be
used ideally in the
3R60 (left) and
3R60-Pro (right)
polycentric prosthetic
knee joints.
The Iglidur piston ring
for a pneumatic prosthetic
knee joint has a
special shape and was
developed and manufactured
to meet Otto
Bock’s specifications.
Photo: Otto Bock
Photo: Igus
A
prosthesis has to be fit to each individual
wearer and support the body
during challenging physical activities, like
running. To make these requirements
seem natural and as comfortable as
possible for wearers of prosthetics, Otto
Bock SE & Co. KGaA, based in Duderstadt/
Germany, has spent years developing innovative
products like the C-Leg: When
first introduced in 1997, it was the world’s
first microprocessor-controlled knee joint
that measured movements in real time.
Wearers of this prosthesis can, for
YOUR KEYWORDS
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Plain bearings for prosthetic knee joints
Self-lubricating
Replacement for metal solution
Tests under load
Advantage for limited space
example, direct their gaze ahead when
walking through the forest instead of having
to keep an eye on the ground at all
times.
To be able to develop these devices,
Otto Bock has been working very closely
together with prosthesis wearers with the
goal of understanding their needs. For
everyday activities, these people want coordinated
movement sequences, good
shock-absorbing properties, and a functional
capacity at least equal to the natural
joint.
Some of the bearing zones in prosthetic
knee joints used to have bronze
bearings. But the experts at Otto Bock determined
that fretting corrosion can be
common when small pivoting movements
are made. This can make knee joints stiff
and pose a risk to people with prosthetics.
Several materials were tested in the
search for an alternative. Ultimately, the
prosthetics specialist decided to use Iglidur
polymer plain bearings made by Igus
GmbH in Cologne/Germany. They are optimised
for use under high friction and
have a very low wear rate. “The plain
bearings are made of a mixture of basic
polymers, fibres, fillers, and solid lubricants,”
states Ulf Hottung, Industry Manager
for Medical Technology at Igus. The
solid lubricants are embedded in the solid
material as microscopically small particles.
“This is enough to lubricate the immediate
environment adequately and to
do away with external lubricants like oils
and greases.”
In its own testing lab, Otto Bock examined
more closely just what these bearings
can do. Prosthetic knee joints with
the Iglidur plain bearings were bent
under load to gain knowledge about the
wear behaviour of the components under
realistic conditions.
Otto Bock made the decision to use Iglidur
bearings not only because they are
corrosion resistant. They offered other
advantages for prosthetic knee and hip
48 medicine&technology 01/2019