Page 25 - KNEETA

FATIGUE WEAR
Continuous cyclical loading and unloading of components, which
leads to subsurface cracks that propogate to the surface, causing
formation of particles that are shed.

Grinding of debris (polyethylene, metal, bone, cement)
between articulating surfaces, leading to scratches in the bearing
material which accelerate wear on the metal and polyethylene non-crosslink
articular surfaces.
non-crosslink Non-Crosslinked
MicroPort Orthopedics’s DURAMER®
polyethylene balances several material
properties to provide high performance.

RESIN PROPERTIES
The ASTM (American Society for Testing and Materials) committee
recognizes three ultrahigh-molecular-weight polyethylene
(UHMWPE) resin types for use in biomedical devices. DURAMER®
is composed of the strongest of the three types (Type I). This resin
has higher yield strength and impact strength than any other
polyethylene resin commonly used in biomedical devices.

EtO (Ethylene Oxide) STERILIZATION

properties. Gamma sterilization has been known to increase free
radical concentration compared to EtO sterilization. After EtO
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sterilizing a crosslinked polyethylene three times sequentially, crosslink Crosslinked
it was determined the material properties were unchanged.
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FIGURE 2 MPa crosslink
0 0 0 0 0 0 0 FIGURE 3 | Non-crosslinked and crosslinked polyethylene chains
0 1 2 3 4 5 6 7
Standard
Polyethylene
1x EtO MPa
h 0 0 0
t 0 0 0 0 0 2 4
g 0 2 4 6 8 1 1 1
e n
t e
a r Crosslinked
m t S Polyethylene
i
t e 1x EtO Standard
l l
U i s PE
n h
Te t g
Crosslinked n
Polyethylene e r Crosslinked
3x EtO t S Polyethylene
1x EtO
ct
a
p
FIGURE 2 | Ultimate Tensile Strength of DURAMER® (1x EtO), Crosslinked m I Crosslinked
Polyethylene (1x EtO), and Crosslinked Polyethylene (3x EtO) Polyethylene
3x EtO
Crosslinking changes the linear polyethylene molecule to have a
branched pattern. FIGURE 3 Varying levels of crosslinking (known FIGURE 4 | Impact Strength of DURAMER® (1x EtO), Crosslinked Polyethylene (1x
as “crosslink density”) is possible. Increasing the crosslink density EtO), and Crosslinked Polyethylene (3x EtO)
of polyethylene lowers several material properties and introduces
free radicals into the material, which will oxidize the material over reported in the FDA’s MDR website, where all failures are reported.
time. FIGURE 4 The reduction in knee wear from crosslinking This modest gain in wear performance in the knee makes it
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reduction, contact stresses are higher in the knee than in the hip, impact strength) from crosslinking.
suggesting that higher material strength may be required for knee
applications. Incidence of tibial insert fractures of conventional
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SUNTEK KNEETA R
Medical Devices
and Electronic
Products Trade Co. KNEETA® Medial-Pivot Knee System Total Knee system
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