artificial disc replacement 2015
TRANSCRIPT
Artificial Disc Replacement
GEORGE SAPKASPROFESSOR AT ORTHOPAEDICS
Metropolitan Hospital Athens
GREECE
A new term which is used more and more
in international scientific meetings and
publications starts to dominate the
scenery:
“Spine Arthroplasty”
Spine Arthroplasty
The last three decades have been the
most revolutionary in the history of spine
treatment.
The 80’s
were dominated
by the development
of modern implants
for internal segmental
fixation such as
pedicle screw systems
and others.
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
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.
At the beginning of this century,
the progress in implant technology
open a new dimension for
spinal reconstructive
non-fusion surgery.
A variety of new implants for:
nucleus pulposus
total disc replacement
dynamic posterior reconstruction systems,
posterior shock absorbers
injectable intradiscal materials
are used today.
Cervical Spine
Biomechanics of Cervical Disk
Replacement
Cervical Spinal Unit : Degeneration
Τhe mechanics of the human cervical spine inνiνο are a result of :
• bending around different axls
• Shear
• axial compression forces.
Cervical Intervertebral
Total Disc Replacement
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…
Criteria for patient enrollment in the USA
Inclusion criteria
Unresponsive to nonoperative treatment for 6 weeks, or presence ofprogressive 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
Criteria for patient enrollment in the USA
Exclusion criteriaMore than one vertebrallevel requiring treatment
Marked cerνical instability on resting lateral orflexion/extension radiographs
a. translation greater than 3 mm and/orb. 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 ordegeneration
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…
Criteria for patient enrollment in the USA
Exclusion criteriaSevere spondylosis at the level to be treated as characerized by any of the following:
a. bridging osteophytesb.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
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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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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United HealthCare Services, Inc.
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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Goals of the cervical spine disk prosthesis
Stabilize a segment following diskectomy
Preserve "physiological" range of motion ofapproximately 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 thesegment
Take compression forces of at least 1200 Ν
Bryan Cervical Disk Replacement
DESIGN OBJECTIVES
Provide range of motion
(ROM) to permit normal
function
Long-term stability
Durability: withstand
loads of ADL for >10
years
DESIGN FEATURES
Shell with
Rigid Wings
Sheath
(shown cut away)
Retaining Wires
(shown cut away)
Nucleus
Porous Coating
on Shell Dome
DESIGN FEATURESShell
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
OBJECTIVE: ELASTICITY
Polymer nucleus has elasticity more like
natural disc (vs. UHMWPE)
May help protect adjacent levels against
excessive loads
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
OBJECTIVE: CONSTRAINT
Unconstrained over normal ROM
Semi-constrained in maximum ROM: Internal geometry and mechanics provides “soft” stops
Mechanically stable against dislocation or subluxation
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
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
The Prodisc-C:
Concept for
Cervical Disk
Arthroplasty (semi-constrained)
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.
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.
ACDF vs ProDisc-C
ACDF vs ProDisc-C
ACDF vs ProDisc-C
ACDF vs ProDisc-C
ACDF vs ProDisc-C
ACDF vs ProDisc-C
Chord compression at C4-C5 left side
Lateral view after
Prodisc-C implantation
ΑΡ view after
Prodisc-C implantation
MRI pre-surgery.
DDD multilevels -
Chord
compression at C4-
C5
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
Further
investigations
Artificial Disc Replacement
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?
Lumbar Spine
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.
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.
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.
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.
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.
Lumbar Intervertebral
Total Disc Replacement
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.
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
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.
Lumbar disc replacement
IndicationsAge 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
Lumbar disc replacement
ContraindicationsSymptomatic
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
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
Gravius S. et al Medicine 2007
Properties of types
of prostheses
that are currently
available on the market
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.
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”
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.
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
SB Charité
The SB Charité
prosthesis is the
most widely used so
far.
SB Charité prosthesis
has „unconstrained“
kinematics.
SB Charité
A biconvex polyethylene
core lies between
two cobalt chromium
moblydenum alloy
(CrCoMo) endplates,
which are coated with
hydroxyapatite to
enhance
osseointegration.
SB Charité
The endplates
grip the adjoining bony
endplates by means
of three metal teeth,
which are attached
anteriorly and posteriorly
and run diagonally.
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.
A-Mav™
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
Maverick Implant Design
Inferior ComponentSix sizes available:
Width
32mm (S)
35mm (M)
39mm (L)
Superior ComponentEighteen sizes available:
Height
10mm
12mm
14mm
Lordosis
6°, 9° or 12°
Depth
25mm (S)
27mm (M)
30mm (L)
Extension Bending
(Standing)
+2°
(Total 15° ROM)
+4°
Lateral Bending
-4°
(8° Total ROM)
Lateral Bending
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“.
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.
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
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.
LUMBAR DISC
PROSTHESIS
Mobidisc ®
(semi-constrained)
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
Mobidisc® components
Adjustable keel
Superior plate
Mobile insert
Inferior Plate
Adjustable keel
Spherical contact surface Plane contact surface
Perfect congruence
between the plates and the mobile insert
Mobility
CONTACT SURFACES
INSERT MOBILITY
Neutral
position 4 stops
avoiding the
nucleus
migration risks
ROTATION CONTROL
Nucleus rotation control
6°
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
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).
Mobility degree
Flexion
Extension+ and - 12°
Lateral + and - 10
Rotation + and - 6°
Insert
rotation2,5 mm / axis
6°
Acroflex disc
The prosthesis has
largely „constrained“
kinematics.
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.
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.
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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