Polyethylene Damage Mechanisms

in Total Hip & Total knee Surgeries

Dr.Sandeep Agrawal,

Bone Joint Surgeon,

Agrasen Hospital,

Gondia

Maharashtra

India

drsandeep123@gmail.com

09960122234

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Delamination

Adhesive/Abrasive

Wear

Pitting

Creep

Cold Flow

Polyethylene Damage Mechanisms

Delamination

Delamination

Delamination occurs due to initiation and propagation of subsurface cracksand can result in the removal of large (>0.5-mm) flakes of polyethylene wear debris.

Crack initiation and propagation occur when materials fatigue following repetitive stresses.

Crack

Tibial insert subjected to compressive stresses immediately under the contact area, with a peak stress at a depth of 1 to 2 mm below the surface

Stresses outside the contact area are reversed and are tensilein nature.

As a result, during the rolling-sliding motion of the femoral component, subsurface region of polyethylene is subjected to completely reversing cycles of stress, i.e., compression and tension.

This fluctuating stress environment is precursor to fatigue, leading to the initiation and propagation of cracks in the material.

Delamination

Primary cause of most polyethylene-related total knee failures

result in loss of geometric conformity

alter pattern of load distribution

eventually result in accelerated implant failure by disengagement or fracture of tibial insert or wear-through .

WEAR :

motion between surfaces loss of

material from the surfaces of the prosthesis

plastic deformation

CREEP implant shape change, not

causing loss of material or producing

particulate debris

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Wear

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Adhesive wearAbrasive wear

Transfer wear

Fatigue wear

Third body wear

Adhesive/Abrasive Wear

contributes to implant failure mainly by

generating particulate debris that

results in periprosthetic osteolysis

Abrasive wear

Generation of wear debris from the

cutting and removal of the soft

polyethylene articular surface by hard

asperities on the femoral component

By hard third-body particles, such as

bone chips or bone-cement particles

Adhesive Wear

Adhesive wear causes removal of

small particles of wear debris, usually

a few micrometers or smaller in size

It is initiated by orientation and strain

hardening of the implant surface

Adhesive Wear

M-G I PE s/p 10y/o

Lace or ripple ,are

the likely

precursors to

adhesive/abrasive

wear

ripplelace

Adhesive Wear

Occurs at primary articulations, i.e.,

the tibiofemoral and patellofemoral

articulations, and at backside,and

tibial post-cam articulation of posterior

stabilized total knee designs

Pitting

Pitting is another fatigue-related phenomenon

results from the coalescenceof shallow subsurface cracksor cracks initiated on the surface

occurs mostly on the articular surfaces, does not result in a substantial loss of material.

Creep

Permanent deformation resulting from

prolonged application of a stress

below the elastic limit

Creep

Deformation that occurs over period of time when a material is subjected to constant stress at constant temperature

In metals, creep usually occurs only at elevated temperatures.

Creep at room temperature is more common in plastic materials and is called cold flow or deformation under load.

Cold flow

Permanent deformation of plastics

remaining after load applied at

temperature below distortion

temperature is removed.

It is an alternate term for creep in

plastics (ASTM D-674) and rubber

(ASTM D-530).

Cold flow

The distortion, deformation, or

dimensional change which takes

place in materials under continuous

load at temperatures within the

working range (cold flow is not due to

heat softening).

Polyethylene Damage Mechanisms

extent of oxidative embrittlement of the polyethylene resulting from gamma sterilization in air

stress state of the components

implant design

PS designs generally have more conforming

articulating surfaces than CR type, lower stress levels

polyethylene thickness

thicker inserts provide more cushioning and

lower stresses in the polyethylene than do thinner ones

soft-tissue stability

component alignment

method of sterilization of

polyethylene components

gamma irradiation in air 55% Delamination

reaction of oxygen with the residual free radicals that are

generated by gamma irradiation, leads to the degradation of the

mechanical properties of polyethylene.

embrittlement

ethylene oxide gas 0% Delamination

resin type and the consolidation

method affect the delamination

resistance

Himont 1900 polyethylene resin in

combination with direct compression-

molding has been shown to have

superior resistance to delamination

ram-extruded GUR 4150 resin

Application of crosslinking technology

in total knee replacement

high-dose radiation used to achieve a

high crosslink density

followed by melting to eliminate the

residual free radicals

substantially increases the

delamination resistance of

polyethylene after accelerated aging

Application of crosslinking technology

in total knee replacement

The preliminary in vitro knee simulator testing of highly crosslinked polyethylenes suggests that these polyethylenes reduce adhesive/abrasive wear and eliminate delamination

Two types of highly crosslinked polyethylene tibial inserts have been in clinical use for more than one year, and there have been no reports of early in vivo complications.