The document discusses the advancements in spine arthroplasty, highlighting cervical and lumbar artificial disc replacements and their criteria for patient enrollment in the USA. It outlines the indications, contraindications, and the design objectives of various disc prostheses, emphasizing their mechanical properties and the necessity for proper patient selection. Additionally, it addresses the uncertainties regarding long-term outcomes and the potential for degenerative changes in adjacent discs following these surgical interventions.

1. Artificial Disc Replacement
GEORGE SAPKAS
PROFESSOR AT ORTHOPAEDICS
Metropolitan Hospital Athens
GREECE

2. A new term which is used more and more
in international scientific meetings and
publications starts to dominate the
scenery:
“Spine Arthroplasty”

3. Spine Arthroplasty
The last three decades have been the
most revolutionary in the history of spine
treatment.

4. The 80’s
were dominated
by the development
of modern implants
for internal segmental
fixation such as
pedicle screw systems
and others.

5. In the 90’s
„Mini-open“ as well as „closed“ endoscopic
techniques replaced the majority of conventional
surgical approaches
Progress in biological and biochemical research
seems to open new perspectives in fusion
technology

6. We must not forget
that bony fusion
of a functional spinal unit
is non physiological
and it is associated with
a variety of proven
and (yet) unproven undesired
effects and sequelae.

7. At the beginning of this century,
the progress in implant technology
open a new dimension for
spinal reconstructive
non-fusion surgery.

8. A variety of new implants for:
nucleus pulposus
total disc replacement
dynamic posterior reconstruction systems,
posterior shock absorbers
injectable intradiscal materials
are used today.

9. Cervical Spine

10. Biomechanics of Cervical Disk
Replacement

11. Cervical Spinal Unit : Degeneration

12. Τhe mechanics of the
human cervical spine in
νiνο are a result of :
• bending around
different axls
• Shear
• axial compression
forces.

20. Cervical Intervertebral
Total Disc Replacement

21. Criteria for patient enrollment in the USA
Inclusion criteria
Symptomatic cerνical disk disease in only
one vertebral level between C3 –C7 defιned
as neck or arm (radicular) pain, and/or
functional/neurologic defιcit with at least
one of the following conditions confιrmed by
imaging (CT, MRI, or X-rays)
Herniated nucleus pulposus
Spondylosis (presence of osteophytes)
loss of disk height
Age between 18 and 60 years
Cont…

22. Criteria for patient enrollment in the USA
Inclusion criteria
Unresponsive to nonoperative
treatment for 6 weeks, or presence of
progressive symptoms or signs of
nerνe root/spinal cord compression
Neck Disability Index [13] score
greater than or equal to 15/50 (30%)
Psychosocially, mentally, and
physically able to comply with the
postoperative protocol
Signed informed consent

23. Criteria for patient enrollment in the USA
Exclusion criteria
More than one vertebrallevel requiring treatment
Marked cerνical instability on resting lateral or
flexion/extension radiographs
a. translation greater than 3 mm and/or
b. greater than 11 ο of angular motion
Has a fused level adjacent to the level to be treated
Radiographic confιrmation of severe facet joint! disease or
degeneration
Known allergy to cobalt, chromium, molybdenum, titanium,
or polyethylene
CΙinically compromised vertebral bodies at the affected
level(s) due to current orΓ past trauma, e.g., radiographic
appearance of fracture callus, malunion, or nonunion
Prior surgery at the level to be treated
Cont…

24. Criteria for patient enrollment in the USA
Exclusion criteria
Severe spondylosis at the level to be treated as characerized by any of
the following:
a. bridging osteophytes
b.loss of disk height greater than 50 %
c. absence of motion < 20)
Neck or arm pain of unknown etiology
Osteoporosis: If DEXA is required, exclusion defιned as Τ score less
than ΟΓ
equal to -2.5 [14]
Paget's disease. Osteomalacia, or any other metabolic bone disease
Severe diabetes mellitus requiring insulin
Pregnant or possible pregnancy ίη next 3 years
Active infection - systemic or local
Concurrent drugs that affect healing (e.g..steroids)
Rheumatoid arthritis ΟΓ other autoimmune disease
Systemic disease. e.g.. AIDS. ΗIV. hepatitis
Active malignancy

25. Cervical artificial disc replacement is
proven and medically necessary for
treatment of persons with symptoms
of degenerative disc disease
at one level
even if they have radiological evidence
of degenerative disc disease at multiple
levels.
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26. Cervical artificial total disc replacement
is proven and medically necessary for
the treatment of symptomatic
contiguous two level degenerative disc
disease
in skeletally mature patients when used
according to U.S. Food and Drug
Administration (FDA) labeled
indications.
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27. Cervical artificial disc replacement
at one level combined
with cervical spinal fusion surgery at
another level (adjacent or non-adjacent)
performed at the same surgical setting
is unproven and not medically
necessary.
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28. Goals of the cervical spine disk prosthesis
Stabilize a segment following diskectomy
Preserve "physiological" range of motion of
approximately 100 in every motion plane
Resist bending moments of at least 2.5 Nm applied
to the segment
Resist shear forces of at least 40 Ν applied to the
segment
Take compression forces of at least 1200 Ν

30. Bryan Cervical Disk Replacement

31. DESIGN OBJECTIVES
Provide range of motion
(ROM) to permit normal
function
Long-term stability
Durability: withstand
loads of ADL for >10
years

32. DESIGN FEATURES
Shell with
Rigid Wings
Sheath
(shown cut away)
Retaining Wires
(shown cut away)
Nucleus
Porous Coating
on Shell Dome

33. DESIGN FEATURES
Shell
Wings: anterior stop
Post: “soft” stop in maximum ROM
Internal polished concave spherical surface
External convex surface with porous coating
Low friction, wear resistant, elastic material.
2 convex spherical surfaces
Nucleus

34. OBJECTIVE: ELASTICITY
Polymer nucleus has elasticity more like
natural disc (vs. UHMWPE)
May help protect adjacent levels against
excessive loads

35. OBJECTIVE:
RANGE OF MOTION
Articulates via axially symmetric spherical
bearing surfaces
11° of F/E and lateral bending
2 mm translation
Rotationally unconstrained
Motions also determined by soft tissue
interactions
– Allows coupled motion of normal spine
– Maintains normal biomechanics of adjacent
FSU’s

36. OBJECTIVE: CONSTRAINT
Unconstrained over
normal ROM
Semi-constrained in
maximum ROM:
Internal geometry and
mechanics provides
“soft” stops
Mechanically stable
against dislocation
or subluxation

37. OBJECTIVE:
ACUTE STABILITY
Machined endplates
provide interference fit
Porous coating: high
friction between bone/shell
Polished shell: low friction
between shell/nucleus
– minimizes stress transfer to
implant/bone interface

39. Bryan disc prostheses
SUMMARY
Prosthesis performance has been
challenged in static, dynamic, fatigue,
durability and in vivo “worst case” models
All results have exceeded design
requirements with adequate factor of
safety

40. The Prodisc-C:
Concept for
Cervical Disk
Arthroplasty
(semi-constrained)

44. Biomechanical choices
The design has been
a ball-and-socket joint,
with a radius of motion
and a center of rotation
compatible with those remaining
posterior structures
This semiconstrained concept
is the only one acceptable
after the anterior release
that removes ΑLL, ΡLL, and disk.

45. The primary anchorage
is provided by a keel that stabilizes
the implant;
Secondary anchorage will be
provίded by osteointegration.
The range of motion covers
20° in flexion-extension
(physiologically around 17°),
20° in lateral inclinations (11°),
and unlimited rotation (12°).
The posterior elements retain as
much physiological control over the
range of the mobility as possible.

46. ACDF vs ProDisc-C

47. ACDF vs ProDisc-C

48. ACDF vs ProDisc-C

49. ACDF vs ProDisc-C

50. ACDF vs ProDisc-C

51. ACDF vs ProDisc-C

52. Chord compression at C4-C5 left side
Lateral view after
Prodisc-C implantation
ΑΡ view after
Prodisc-C implantatio
MRI pre-surgery.
DDD multilevels -
Chord
compression at C4-
C5

53. Chord compression
at C5-C6 pre-surgery
Flexion and Extension
after Prodisc-C
implantation at level C5-
C6
Prodisc – C in neutral
position and in lateral
bending

55. Further
investigations
Artificial Disc Replacement

56. Is the implantation
procedure less invasive
than interbody fusion with a
cage?
Can segmental mobility be
achieved and/or
maintained?
Can the physiological
curvature be restored and
retained?
What will be the rate of
spontaneous fusions?
How does the implant
behave iη the long term?

57. Lumbar Spine

58. Nucleus replacement
implants/ partial disc prosthesis
The optimal indication for
artificial nucleus
replacement is
monosegmental
degenerative discopathy.
Lumbar pain should be the
main symptom.
For a PDN prosthesis, the
disc height should be at
least 5 mm.

59. Nucleus replacement
implants/ partial disc prosthesis
For the other types of
nucleus replacement
implants,
the disc height
should be at least 10 mm
due to the lack
of capacity for expansion.

60. Nucleus replacement
implants/ partial disc prosthesis
A sufficiently stable
annulus container should
be documented by
discography; a pain
provocation test can be
carried out at the same time
and the disc confirmed as
the origin of pain.

61. Nucleus replacement
implants/ partial disc prosthesis
For a PDN prosthesis, the
sagittal diameter of the
nucleus should be at least
26 mm to allow sufficient
room for the ventral and
dorsal implant.

62. Nucleus replacement
implants/ partial disc prosthesis
Other indications, such as
post-nucleotomy syndrome
or primary disc prolapse, are
still undergoing clinical
evaluation.
Reliable results are not yet
available.
The use of nucleus
prostheses for these
indications therefore cannot
be recommended at present.

63. Lumbar Intervertebral
Total Disc Replacement

64. An artificial intervertebral
disc ought to have the
same biomechanical
properties as the body's own
discs
with regard to segmental
height,
the normal excursion of
segmental motion,
and the normal degree of
lumbar lordosis.

65. Pathological movement
properties must be corrected
to optimize the function of the
adjacent segments
and to avoid non physiological
stresses.
The prosthesis should be safely:
Implantable
Safely removable
Replaceable

66. The following important requirements
should be placed on any modern type of
functional disc replacement:
Optimal mechanical durability of the
biomaterials used
Bio-compatibility of the materials used and of
the particles that will be rubbed off of it by
wear and tear
Possibility of noninvasive postoperative
imaging.

67. Lumbar disc replacement
Indications
Age 30 to 50 years (20)
Discogenic low back pain due to monosegmental
disc degeneration at L4/5 or L5/S1
Lack of response to at least 6 months of conservative
treatment
Back and/or leg pain without evidence of nerve root
irritation (normal electrophysiological findings)
Oswestry score (ODI) 30
VAS score 40 (100)
Gravius S. et al Medicine 2007

68. Lumbar disc replacement
Contraindications
Symptomatic
multisegmental disc
degeneration
Posttraumatic segment
Postoperative segment
(except post-discectomy)
Infection
Spinal tumor
Facet joint arthrosis
Spondylolysis
Spondylolisthesis > 3 mm
Spinal canal stenosis
(diameter < 8 mm) and
recess stenosis
Scoliosis > 11°
Osteoporosis, osteopenia,
metabolic bone disease
Autoimmune disease
Pregnancy
Morbid obesity (BMI > 40)
Metal allergy
Gravius S. et al Medicine 2007

69. Bertagnoli and Kumar postulated 4 criteria
that together define the optimal patient
profile for the implantation of a disc
prosthesis:
Disc height > 4 mm
No degenerative changes of the facet joints
No degeneration of the adjacent segments
Intact posterior spinal elements without any
pathological changes.
Bertagnoli R. et al Eur Spine 2002

70. Gravius S. et al Medicine 2007

71. Properties of types
of prostheses
that are currently
available on the market

72. The first-ever disc prosthesis, described by
Fernstrom in 1950, consisted of a
stainless steel sphere that was implanted
in the intervertebral space.
Since then, more than 100 types of
mobility-preserving intervertebral implants
have been described in the literature.

73. Modern disc prostheses
are firmly anchored
in the upper and lower endplates
of the vertebral bodies adjacent to the
degenerated disc by metal plates
and have a sliding central component
made of ultra-high-molecular-weight
polyethylene.
Such prostheses can be of either
“constrained“
"semi-constrained“
"non-constrained”

74. In prostheses of the former type,
the inlay is fixed in the endplate of the lower
vertebral body
and therefore possesses a fixed center of
rotation,
around which only flexion/extension
and lateral bending movements can take
place.

75. In contrast,
the sliding central component
of non-constrained prostheses
can move freely;
the center of rotation does not have a fixed
location,
translational
and
rotational movements of the prosthesis
remain possible

76. SB Charité
The SB Charité
prosthesis is the
most widely used so
far.
SB Charité prosthesis
has „unconstrained“
kinematics.

77. SB Charité
A biconvex polyethylene
core lies between
two cobalt chromium
moblydenum alloy
(CrCoMo) endplates,
which are coated with
hydroxyapatite to
enhance
osseointegration.

78. SB Charité
The endplates
grip the adjoining bony
endplates by means
of three metal teeth,
which are attached
anteriorly and posteriorly
and run diagonally.

79. SB Charité
Due to the biconvex
shape of the polyethylene
core,
the intervertebral disc
space also has to be
distracted more when
using the SB Charité
prosthesis
as compared to the other
types of prosthesis in order
not to damage the
polyethylene.

80. A-Mav™

81. Maverick Implant Design
HA Coating
Calcium phosphorus
Provides a geometry
which is conductive to
bony on growth
Rough surface provides
increased friction for a
press fit

82. Maverick Implant Design
Inferior Component
Six sizes available:
Width
32mm (S)
35mm (M)
39mm (L)
Superior Component
Eighteen sizes available:
Height
10mm
12mm
14mm
Lordosis
6°, 9° or 12°
Depth
25mm (S)
27mm (M)
30mm (L)

84. Extension Bending
(Standing)
+2°
(Total 15° ROM)

85. +4°
Lateral Bending

86. -4°
(8° Total ROM)
Lateral Bending

87. Prodisc II
This type of prosthesis
and its precursor model
have are the second
most commonly used.
In terms of its
kinematics, the
prosthesis can be
described as largely
„semi-constrained“.

88. Prodisc II
Like the SB Charité
prosthesis,
it consists of two
endplates made of a
CrCoMo alloy
with a pure titanium
Plasmapore®
surface to improve
osseointegration.

89. Prodisc II
In contrast to the SB
Charité prosthesis,
a monoconvex polyethylene
core is used in the Prodisc
prosthesis
and is inserted in the caudal
endplate using a
multifunctional instrument;
once the polyethylene core is
firmly anchored to the caudal
endplate, there are two
movable parts

90. Prodisc II
In contrast to the SB
Charité prosthesis, luxation
of the polyethylene core
cannot occur when Prodisc
II is used.
ProDisc II can be
positioned best even if
space is limited due to the
anatomic conditions or if
the course of the
vasculature is unfavorable.

91. LUMBAR DISC
PROSTHESIS
Mobidisc®
(semi-constrained)

92. SPECIFICITIES
Reduces the stress on the posterior articular
process with the help of the instantaneous
centre of rotation preservation.
self control Nucleus stabilization
self-centering of the superior plate together
with the inferior plate.
Lateral, antero-lateral or medial access with
the same prosthesis.
Prosthesis with controlled mobility

93. Mobidisc® components
Adjustable keel
Superior plate
Mobile insert
Inferior Plate
Adjustable keel

94. Spherical contact surface Plane contact surface
Perfect congruence
between the plates and the
mobile insert
Mobility
CONTACT SURFACES

95. INSERT MOBILITY
Neutral
position 4 stops
avoiding the
nucleus
migration risks

96. ROTATION CONTROL
Nucleus rotation control
6°

97. Insert mobility
Adapts to the instantaneous centre of rotation :
Favours the decrease of :
the stress on the articular facets
the implant wear
of the prosthesis-bone constraints
transmission

98. Insert Mobility
Self-centering :
The anterior translation of the superior plate
leads to a posterior translation of the nucleus.
Self-positioning of the nucleus.
Self-centering of the superior plate together
with the inferior plate (no retrolisthesis).

99. Mobility degree
Flexion
Extension
+ and - 12°
Lateral + and - 10
Rotation + and - 6°
Insert
rotation
2,5 mm / axis
6°

100. Acroflex disc
The prosthesis has
largely „constrained“
kinematics.

101. Acroflex disc
The two titanium endplates
are joined together by an
HP-100 silicone elastomer
core.
Osseointegration occurs via
a rough surface and via
small spikes attached to the
ventral third.
The prosthesis is inserted
as a whole using centrally
inserted distraction forceps.

102. Acroflex disc
In contrast to the two other
types of prostheses,
transmission of motion
only works if there is good
osseointegration of the
endplates.
Unfortunately, fissures
have repeatedly been
observed in the elastomer
Core.

103. Statement
Lumbar artificial total disc replacement is unproven
for the treatment of single or multiple level
degenerative disc disease in skeletally mature
patients.
The long-term clinical outcome of lumbar disc
replacement is unclear.
The evidence from uncontrolled long-term studies
suggests that potential degeneration of adjacent
discs and facets and wear of the polyethylene part of
the disc may occur and that, in some cases, revision
surgery may be needed.
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