Paris 2003

Wear of UHMWPE cup and component loosening in total hip arthroplasty

Professor B.M. Wroblewski

P.D. Siney

P.A. Fleming

The John Charnley Research Institute

Wrightington Hospital, U.K.

Mechanical v BiologicalA scientific controversy ?

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“The late failure if it does eventually supervene, is to be expected from one, or both, of two possible causes –

1. Tissue reaction to particles abraded from the bearing surfaces

2. Mechanical loosening of the cement bond in the bone.”

Sir John Charnley 1967

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Cup Wear & Migration

0

20

40

60

80

100

0 1 2 3 4 5 6 7

Wear (mm)

% Cases

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“… socket wear ... and the resultant cup loosening … appears to be the one factor

limiting the life of the arthroplasty.”

BM Wroblewski 1985

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Removal or transfer of material from articulating surfaces due to their relative

movement under load.

British Standards Institution 1979

Wear :

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Wear measurement :

- Change of mass

- Volume measurement

- Depth of wear tracks (penetration : depth and rate)

British Standards Institution 1979

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Continuous deformation of a material when subjected to stress over an extended period.

Change of dimensions without loss of material

Creep :

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“… granulomatous tissue may act on the neighbouring bone … which is removed by extensive resorption leading to loosening of

the prosthesis.”

Willert & Semlitsch

Biocompatibility of Implant Material 1976

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“… the chief clinical question is that of biological effects of the debris and not the mechanical problems due to dimensional

changes.”

RM Rose et al JBJS 1980

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“… only 10% of volumetric changes are caused by wear, whereas creep is responsible for the other 90%”

RM Rose et al JBJS 1980

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“ Cement disease”

“ Cementless disease”

“Particle disease”

“Access disease” – “Effective joint space”

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Wear Volume – ‘Cylindrical’

Volume r2 x d

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Mechanical v Biological causes of component loosening in total hip arthroplasty.

A scientific controversy ?

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The study of those judgements

concerning which universal agreement

can be achieved

Science

Campbell 1921

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A publicly and persistently

maintained dispute

Controversy

Campbell 1921

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Scientific controversy does not concern the facts :

- component loosening -

It concerns explanation of the facts :

- the cause of component loosening -

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Scientific controversy rests on the

assessment of the reason for action

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NOT : is there tissue reaction to wear particles

BUT : is tissue reaction to wear particles

responsible for component loosening ?

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- Loss of interest - Force- Consensus : does not resolve the basic issue- Negotiation : common in politics- Sound argument closure

Resolution of Controversy

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- correct position is reached - in the context of the controversy - making the opposing view unjustified

Sound argument closure

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Essential to promote progress

Controversy

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Three aspects- The facts- The explanation of the facts- Proposed solutions

Controversy

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Component loosening : not disputed but -

IncidenceInterpretation of radiographic appearancesClinical presentationIndications, timing and method of revision

may be open to debate and dispute

Controversy : The Facts

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Mechanical or Biological ?

The main aspect of the controversy as it dictates the line of action

Controversy :The explanation of the facts

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- Tissue reaction to wear particles- Bone resorption- Component loosening

Solution- Modify tissue reaction- Change the materials

Biological

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- Outer cup wear : B.M. Wroblewski JBJS 1987

- Head damage : increased frictional resistance R.M. Hall et al B.J. Rh 1997

- Thinning of plastic cup shell : fatigue type processR.M. Hall et al Ibid

- Increased frictional torque : Cup size 30 < 40 < 43

- Impingement B.M. Wroblewski JBJS 1985

Mechanical :

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- Theoretical consideration B.M. Wroblewski 1985

- Practical results (1982 : 10mm diameter neck)

- 12.5 mm : impingement at 0 wear 10.0 mm : at 2 mm wear

Mechanical : reduced diameter neck (12.5mm 10mm)

} 50% probabilityR.M. Hall et alJ. Orth. Sc. 1998

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Acetabular Pressurizerand revision for aseptic cup loosening

Survivorship Analysis

50

75

100

0 4 8 12 16 20 24

Follow-up (years)

% S

urvi

vors

hip

Used

Not Used

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75

100

Follow-up (years)

% S

urvi

vors

hip

Bone block used

No bone block

Distal closure of the medullary canal with cancellous bone block and revision for aseptic stem loosening

Survivorship Analysis

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16 year results : 0.2 – 0.41 mm total penetration

Mechanical : Alumina Ceramic / XLPE

0.0

0.5

1.0

0 4 8 12 16Follow-up (years)

Tot

al p

enet

rati

on (m

m) Alumina Ceramic

Young patients - 0.1 mm/yr

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398 cases : 80.4% no measurable wear

Mechanical : Zirconia Ceramic / UHMWPE

0.0

0.3

0.6

0 1 2 3 4 5 6 7 8

Follow-up (years)

Rate of penetration (mm/yr)

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- Tuberculosis- OA cysts- Wear without cavitation- Healing of Teflon granuloma

Clinical observations

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Intrapelvic teflon granuloma

Orthopaedics International, 1995

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- Low Wear = penetration 0.02 mm/year

- High Wear = penetration 0.2 mm/year

Low Wear v High Wear

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Low Wear v High Wear

Low Wear High Wear

Number of cases 190 149

Average age 41 years 40 years

Average follow-up 15.6 years 13.1 years

Cup revision 5.3% 40.0%

Stem revision 5.3% 7.4%

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0

25

50

75

100

0 4 8 12 16

Follow-up (years)

% S

urvi

vors

hip

Low Wear

High Wear

Low Wear v High Wearand revision for aseptic CUP loosening

Survivorship Analysis

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0

25

50

75

100

0 4 8 12 16

Follow-up (years)

% S

urvi

vors

hip

Low Wear

High Wear

Low Wear v High Wearand revision for aseptic STEM loosening

Survivorship Analysis

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- Fix components well- Reduce wear (Ceramic v UHMWPE)- Avoid strain shielding

Conclusions

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What is revealed is interesting

What is concealed is vital

When it comes to WEAR

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“To know is science. To believe one knows is ignorance”

Hippocrates 460 – 400 BC