artificial disc replacement 2015

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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