1. Metal on Metal
resurfacing Tot. Hip.
Dr F M C van den Eeden
F.M.C.
Orthopedisch chirurg
M.C.A.
M C A Alkmaar
In 2007 : > 23000 artificial total hips implanted in
the Netherlands
Less than 1000 Resurfacing type
In 2010 RECALL of hipprosthesis by Depuy
orthopedics (Johnson & Johnson)
-ASR Resurfacing system
-ASR XL Acetabular system

2. 13% reoperations before 5 y
p
93000 recall worldwide
Early revisions MOM related to
wear
Metal on Metal Hip Resurfacing
- Tribology and Critical Issues
Jack Thomas
Regional Director - Europe
Corin Group p
p plc

3. Background
Resurfacing is not new
R f i i t
Metal-metal bearings are not new
Development of modern metal-metal resurfacing
What went wrong with historical Resurfacing Arthroplasty
What went wrong with historical Metal-metal Arthroplasty
Technical theory behind the Cormet
Clinical and In Vitro Studies
Clinical Follow-up
p
Hip Tribology
Tribology is: ‘a study that deals with the design,
friction, wear
friction wear, and lubrication of interacting
surfaces in relative motion (as in bearings or gears)’
(WWWebsters)
What factors affect the tribology of hip bearings?
Materials
Loads
Geometry
Sliding speeds
Lubrication theory
L b i ti th

4. Lubrication Theory
y
Lubricating films can separate bearing surfaces
Dental drills, air hockey etc
drills
Thickness of the lubricant thickness primarily depends
on:
Material
Load (up to 3.5x Bw)
Contact stress
Sliding velocity
Conformity
(Radial Clearance/Sphericity) Rotation
frequency
Radial
Clearance
The Bottom line…
h l
Lubricant films are formed during relative motion
If the lubricant film is thicker than the relative
roughness the surfaces will separate
separate.
Define lambda ratio:
Minimum Film Thickness
O
Cumulative Surface Roughness

5. Hydrodynamic Lubrication O ! 3
Lubricant film fully separates the surfaces
This is the ideal regime – effectively zero wear
Motion
M ti Bearing Surface
B i S f
Bearing Surface Motion
Boundary Lubrication O < 1
Lubricant is present but not thick enough to separate the
surfaces
Surfaces can be protected b b
S f b t t d by boundary l b i
d lubricants ( t i
t (proteins,
lipids etc)
Asperities on opposing surfaces contact leading to friction and
p pp g g
wear
Motion Bearing Surface
Bearing Surface
Motion

6. Mixed Lubrication 1 < O < 3
Combination of boundary and fluid film lubrication
Occurs with intermittent motions
Sometimes the surfaces are separated and sometimes not
There is occasional surface contact leading to some surface
wear
Bearing Surface
g
Motion
Bearing Surface Motion
So…
So How do we engineer
Hydrodynamic Lubrication?
1. Engineer the materials
2. Engineer the geometry
Diameter
Radial Clearance
Sphericity

7. Effect of Material
Stiffness (Elastic modulus)
Surface roughness
Bearing Material Elastic Modulus (Gpa) Typical Surface
Roughness, Ra (microns)
Alumina 400 0.005
High Carbon CoCr 200 0.005-0.01
UHMWPE 1 1
Stiffness has a small effect on lubricating film thickness
Surface roughness has a massive effect:
UHMWPE is 200 times rougher than metal or ceramic
Minimum Fil Thi k
Mi i Film Thickness
O
Cumulative Surface Roughness
Effect of Bearing Diameter
Large Bearing Diameters
Large bearing = lower contact stress
Increased sliding speed generates an increased fluid film
BUT sliding distance is increased!

8. What does it all mean?
Metal/ceramic UHMWPE bearings
Rough surfaces/Large radial clearances/Poor sphericity
R h f /L di l l /P h i i
¾ Boundary lubrication
¾ Wear is directly proportional to load and sliding distance
¾ More wear with larger bearing diameters
For Example…
Example
THARIES/Wagner/Freeman Metal-UHMWPE Resurfacings
Massive wear due to large diameter Metal-UHMWPE articulation
Metal UHMWPE
- Wrong Tribology

9. What does it all mean?
Metal on metal bearings
We can achieve very smooth surfaces
(Ra = 0.05 microns)
0 05
We can achieve excellent sphericity (<10 microns)
We can achieve optimum radial clearances
Therefore we can achieve a
lubricated contact!
• Especially with
Larger diameter bearings
For Example:
Metal on metal simulator study, Smith et al*
study al
7
llion cycles
s
6
5
We Rate mm per mil
4
m3
3
2
ear
1
0
16mm
16 22.225mm
22 225 28mm (new)
28 ( ) 28mm (worn)
28 ( ) 36mm
36
Joint Diameter
* Proc Inst Mech Eng [H] 2001; 215(2): 161-170

10. What went wrong with Historical M-M
h ih i i l
Hip Arthroplasty?
p p y
Poor Manufacturing tolerances
Equatorial bearing!
Poor design
Component fixation
Impingement
p g
The result?
Early incidence of loosening with metallosis
No such problems with the Charnley at the time.
Summary of Tribology
We know how to engineer the bearing
We know what not to do with
reference to historical Resurfacing and
Metal-metal THRs
So what are the current critical issues
in Metal-metal Hip Resurfacing?

11. Critical Issues?
C iti l I ?
Wear
Do Standard Heat-Treatment Processes Influence
Heat-
Large Diameter Metal-on-Metal Wear ?
Metal-on-
– An In Vitro Study Under Normal & Adverse Gait Conditions
John G. Bowsher, Jim Nevelos, Julia C. Shelton
Trans 49th ORS, New Orleans, 2003
Metal Ion Release
Medium Term Serum Cobalt and Chromium Levels in Patients with
Metal-metal Resurfacing
V Reddy MD, J Dorairajan MD, J Nevelos PhD, S Krikler PhD FRCS(Orth).
Trans 70th AAOS, New Orleans, 2003.
Do Standard Heat-Treatment Processes Influence
Heat-
Large Diameter Metal-on-Metal Wear ?
Metal-on-
– An In Vitro Study Under Normal & Adverse Gait Conditions
Physiological Hip Self-Centring Bearing
Anti-Rotate
Anti Rotate Arm (x2)
Simulator Study Horizontal Torque
y Cell ± 20 Nm
z
As Cast vs HIPed Torque Cell Adapter
x
and Solution
d S l ti Cup Fixturing
Annealed 40mm Serum
Chamber
Direction
of Torque
Measurement T
Bearings 360q
(y-axis)
23q Fixed in
Standard and y-x plane
Severe Testing r23q Biaxial Rocking
Motion
g
Joint
Conditions Force ABD / ADD
FLEX / EXT
(a)(b)
Fig. 1. Schematics showing (a) hip joint simulator, and (b) torque
measurement and definition of biaxial rocking motion.

12. Results
(a) Running-In (b) Steady-State (c) Simulated (d) Simulated
0 to 1 mc 1-3, 4-6 mc Fast Walking Fast Jogging
Normal Walking Normal Walking
7.0 **
6.0 **
(m m 3 /1 0 6 C y c le s )
M ean W ear R ate
5.0
**
4.0
3.0
2.0
m
1.0
0.0
(n=6) (n=8) (n=18) (n=22) (n=6) (n=6) (n=8) (n =8)
(n`=8)
As cast HIPed & Solution Annealed
** - statistically significant
Conclusions – Wear Study
r HIPing and solution annealing did not adversely affect the wear
rates of large diameter metal-on-metal articulations, even under
severe gait conditions.
r Both alloys possessed very different micro-structures and surface carbide
structure, Fig 2a-2b, however, this appeared to have little affect on the
wear mechanisms
mechanisms.
r A combined head and cup wear rate of 0.45 mm3/106 cycles (k = 1.5 x10-8
mm3 N-1 m-1) for the 40 mm diameter metal bearings is lower than that
reported for smaller head diameters, thus suggesting improved lubrication
for larger bearing sizes.
r The wear of both groups was found to be highly sensitive to the type of
patient activity tested, with fast jogging activities generating a 10–fold
increase in metal wear generation compared to normal walking, k = 2.4
x10-7 mm3 N-1 m-1.

13. Medium Term Serum C b l and Chromium Levels
di S Cobalt d Ch i l
in Patients with Metal-metal Resurfacing
Metal-
39 patients followed for up to 6 years
Blood serum levels of Co and Cr measured using a standardized
technique
Two distinct patient groups:
General Population
Outliers
No effect:
Corin McMinn vs. Cormet resurfacing
Bilateral (few data points)
Results – General Population
250 Ov e rall av e rage ion le v e ls
Co
Cr
200
ion level (nmo l/l)
150
100
n
50
0
Pre
Pre- 3 10 16 22 28 34 38 45 52 57 63 76
op Time (months)

14. Younger vs. Older Patient Groups
250 250
ion levels patients under 50 at primary operation ion levels patients over 60 at primary operation
Co
200 200 Co
Cr
Cr
ion level nmol/l
l
150 150
ion level nmol/l
100 100
50 50
0 0
0 3 10 16 22 28 34 39 46 54 0 4 10 16 22 28 33 38 53
Months months
Decrease in ion levels could be due to a decrease in wear after
‘running-in’ plus improved joint stability.
Outliers - Results
4000
AP Co Outliers Compared with Average Population
AP Cr
LB Co
3500
LB Cr
SM Co
3000 SM Cr
Ave Co
Ave Cr
2500
Ion level (nm ol/l)
2000
1500
1000
500
0
0 12 24 36 48 60 72
Months Post-op

15. Conclusions – Metal Ion Study
In the vast majority of patients with metal-metal
hip resurfacing there is a small but early rise in
serum metal ions over the first 2-3 years but the
levels then gradually diminish over time .
g y
Steep cups seem to be associated with increased
levels, which could be due to wear and therefore
increased ion release into the body.
Summary
Cormet has the right tribology for clinical
success and is the product of 11 years
continuous controlled evolution
Cormet is the only resurfacing hi prosthesis
C t i th l f i hip th i
with peer reviewed published wear data and
l
long term i release measurements
t ion l t

16. Cormet Update – July ‘03
Jack Thomas
Regional Director - Europe
Corin Group p
p plc

17. Latest Developments
p
McMinn published a paper in Hip
International
The paper attacks Cormet and
g
heat treatments in general
General
Paper is in a Supplement with the proceedings
from a symposium at EFORT 2002
o sy pos u O 00
Guest editor was G Bannister (MMT user)
Not peer reviewed as such
Lots of inaccuracies
Lots of very poor science
No surprises there then

18. Key points
Alleged: ’94 –HIPed; ’95 – SA ’96 – HIP d and SA
All d HIP d SA, HIPed d
Fact: ’91-’95 – Trucast (94% HIPed)
Fact 1996 – C
F Centaur HIP d and SA (
HIPed d (reverse engineered
i d
from the original McMinn castings).
Difference between HIPed and HIPed and SA?
Negligible
Current Cormet Metallurgy
Unchanged and re-validated

19. More failures in 1996 ??
94-95 – three failures (1 infection, 1 head collapse,
1 loosening with dysplasia)
1996 - 5 failures (1 infection, 3 cup loosenings, 1
awaiting revision)
Metallosis and osteolysis seen with the cup
loosenings
Plus one from Belgium with pain (and alleged severe
wear) at 50 months but well fixed.
)
McMinn Sales by Year
Year No of Implantations.
1991 23
1992 56
1993 57
1994 95
1995 238
1996 440
Total 909

20. Failures with wear
Case from Belgium
with l
ith low carbide
bid
content (allegedly)
Cup is open and
anteverted.
Could be a
yp y
hypersensitivity
reaction
Cup Loosenings
Cups have tilted
HA on smooth
Wear secondary to cup
movement or cup
movement secondary
to wear?

21. Wear as related to carbide content
MMT data (Calowear) from Treacy presentation
1.4E-03
1 4E 03
Error Bars = 1 standard
90% confidence interval
1.2E-03
Wear Coefficien K (mm3 N-1 m-1)
1.0E-03
1.26E-03
1.03E-03
1.03E-03
8.0E-04
9.46E-04
nt,
6.0E-04
4.0E-04
W
2.0E-04
0.0E+00
As Cast HT High N2 HIP & HT
Material Type
100,000 times the wear factors seen clinically!!
Hang on.
McMinn alleges that some 1996
resurfacings are fine and other have
metallosis
Ah, this is because HIP and SA produces
a range of microstructures.
microstructures
A very convenient excuse .
HIP and SA is used because it gives the
most reproducible results

22. Remember…
The data shown by McMinn would lead us to believe
that forged materials also have high wear
200,000 Metasul since 1988 would suggest otherwise
Conserve plus is also HIP and SA with no reported
problems with wear
These arguments are fabrications made up to
support a faulty hypothesis
Published wear data
Mean Volumetric Wear at 3M cycles
7
6
metic Wear (m )
3
mm
5
4
3
Volum
2
1
0
28mm low C 36mm wrought, 36mm wrought, 36mm wrought, 40mm as cast 40mm HIPed and 54mm as cast, 54.5mm as cast,
head/High C cup mean 143 (142-146, mean 123 (120-126, mean 105 (105, (mean 220) SA Mean 220 mean 276 (254-307, mean 108 (83-129,
mean 50 n=3) n=4) n=3) n=3) n=4)

23. Wear Data
Wear is dependant on head size and radial clearance
and NOT metallurgy
Although low carbon/low carbon couples are not great
This was supported at the recent Second International
Conference on Metal-metal Hip Prostheses: Past
Performance and Future Directions. Montreal 2003.
Directions 2003
McMinn d
M Mi and MMT are b becoming i
i increasingly i l t d
i l isolated
by the scientific community and are losing credibility
in the eyes of surgeons.
surgeons
Thank you