15. The cart has been
put before the horse:
the artificial joint has
been made and used,
and now we are trying
to find out how and
why it fails
Charnley 1956
16. Charnley’s 3 major contributions
low friction torque arthroplasty
introduction of high density
polyethylene
use of acrylic bone cement to
secure implant fixation to bone
17.
18. Survivorship
81% at 25 year follow-up
(revision of any component as
end point)
Berry et al 2002
77% at 25 year follow-up
(revision of any component as
end point)
Callaghan et al 2000
(also Kavanagh, Wroblewski, Older, etc)
21. Composite beam
“Shape closed” design
Roughened surfaces
and precoating
contribute to perfect
bond between stem
and cement
22. Taper slip
Highly polished double
tapered stem
Designed to settle in
the cement mantle thus
re-engaging the taper
and becoming
progressively more stable
23. Debonding at the cement-metal
interface represents the initiation
of loosening of cemented femoral
components
Harris 1992
Slip between metal and cement is
essential to protect the cement-
bone interface
Fowler et al 1988
24. Triple tapered stem
? improves loading
of the calcar and
preservation of the
bone in the long term
25. “I think my major
contribution was
the concept of
achieving fixation
entirely by means
of cement”
Charnley 1970
26. Cement is a grout not a glue
the surface area of the truncated cone of
cement presents a much larger surface
area than the stem
when loaded, a cemented prosthesis
transfers the load to the endosteal
surface through hundreds of trabeculae
32. 3M Capital stem
6 year survival of modular
flanged stem: 84%
? rounded medial and lateral
surfaces below the shoulder
reduced torsional stability
? Material (titanium)
33. CEMENT DISEASE
Jones & Hungerford 1987
→ cementless fixation
40. Mid-term results with the
cementless hip replacement
100% survival of the femoral
component at 10 years
Archibeck et al 2001
99% survival of an HA coated
femoral stem at 9-12 years
McNally et al 2000
41. CEMENTED FIXATION
Mechanical interlock: static: quality
of bone, cement and consequently
fixation degrade with time
CEMENTLESS FIXATION
Biological osseo-integration:
dynamic: bone replaced and quality
of fixation maintained
47. Ritter et al (1999) demonstrated
38-fold increase of cup loosening
associated with wear if early post-
operative x-ray demonstrated
bone cement lucency in zone 1
48. Interface can be sealed to exclude
wear debris with PTFE GORE-TEX
membrane + butyl cyanoacrylate
glue
Bhumbra et al 1999
49. physical seal
- membrane excludes fibrous
ingrowth and enhances
osteogenesis
↓
secondary biological seal
56. In an abrasive environment
↓ fracture toughness associated with
an increased number of particles
and
an increased number in the
biologically active range
“Watch this space”
57. Hard-on-hard bearings
Ceramic
↓ surface roughness (Ra 0.02)
wettability
↓ coefficient of friction
hard - not scratch sensitive
58. Ceramic-ceramic
alumina must be of high quality
(roughness/sphericity)
tight tolerances must be
maintained in the manufacture of
the bearing surfaces
clearance must be <10 µ m
59.
acetab
ular
implan
t
should
not be
implan
ted too
60. Advantages
low coefficient of friction
does not degrade with time
minimal wear
0.25 microns per year
4000 x less than M/P coupling
Dorlot 1992
alumina is an inert material and
the wear particles excite a limited
inflammatory response
Lerouge et al 1992
61. Disadvantages
brittle
do not mix and match femoral heads
and morse tapers
avoid scratching the morse taper and
clean thoroughly before applying the
head
avoid heavy hammering
65. Look for new ideas in old
books, because old ideas
are found in new books
66. Early metal-on-metal
articulations had a high rate
of early loosening and failure
stainless steel
small clearance
↓
equatorial bearing with
↑ frictional torque
67. Clearance
optimised clearance ↑ contact area
but avoids equatorial bearing
(minimum 30 - 50 µ m)
↓ angle of convergence ↑ thickness
of fluid film
→ ? fluid film lubrication
68.
69. Metal-metal couple
wear 80 times less than metal on
polyethylene
Metasul
25 µ m during first million cycles
then 4 - 10 µ m per million cycles
Nelson and Dyson
70. Polyethylene Metal-Metal Ceramic-Ceramic
Wear volume mm3/year 30 1.6 1
Particle size (mode) nm 300 30 30 and 500
Number of particles 500 50 000 1 000 to 10 000
billion/year
71. Small particles do not excite an
inflammatory response but are
biologically active
72.
73. Inhibition of cellular response
bisphosphonates directly inhibit
osteoclastic activity
reduce mechanically related
loosening of hip prostheses
74. established ovine model of hemi-
arthroplasty where significant
stress-shielding of the calcar and
medial cortex results in significant
bone resorption at 6 - 12 months
75.
76.
77.
78. Hip resurfacing
Smith Petersen
developed a CoCr
resurfacing head in the
1930s
Charnley used a
resurfacing design in the
1960s
teflon-on-teflon
bearing
very low friction
very high wear!!
90. Coatings have failed due to harsh
environment which has often led
to separation of the coating
However, if successful they could:
improve wear
reduce friction
improve biocompatibility
99. Minimal access surgery
instruments
Position and cut head
Enlarge hole splitting
Drill head head into four sections
Enlarged view of oscillating saw
113. Gene therapy
Gene therapy can be effected by
ex vivo modification with the
gene re-introduced into the
body after modification or
in vivo modification which is
done in situ
114. Can these strategies exert
structure modifying effects to
counteract the disease process?
115. The delivery of genes that
encode the anti-arthritic proteins
may present a biological drug
delivery system
Hendon et al 1999
but...
Safety is an overriding concern
116. Gene delivery vector delivers a
stable gene which permits
stable and regulated production
of therapeutic proteins
117. suppression of the activities of
lymphocyte co-stimulatory
molecules
against anti-lymphocyte antigens
(CDH)
suppression of IL-1 and TNFα
etc
118. Strategies for gene therapy
in arthritis
gene replacement
- substitution of a non-active or
defective gene, e.g. type II
collagen mutation in familial OA
119. gene addition
e.g. IL-1 receptor antagonist
and
gene control, where the
expression of a gene is controlled
e.g. for a specific cytokine
120. onset of OA may be prevented
or delayed by transfection of
articular cartilage chondrocytes
with HPV proto-oncogens which
will slow the progression of
chondrocyte senescence or
replace senescent cells
122. 2010
25% of the population will be
≥ 60 years
40% of these will have arthritis
123. THR is still in the ascendency
for the foreseeable future
124. A surgeon should be as
knowledgeable of the biological
consequences of implanting the
material and prostheses he uses
as the physician is about the side
effects of any drugs he prescribes