Arthroplasty as the Next Evolution for Surgical Reconstruction of the

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Ar throplasty as the Next Evolution for Surgical
Reconstruction of the Spine
a report by
Jack E Zigler, MD
Spine Surgeon and Co-Director of the Fellowship training program, Texas Back Institute and
Clinical Associate Professor of Orthopedic Surgery, University of Texas Southwestern School of Medicine
Jack E Zigler, MD, is a Spine
Surgeon at the Texas Back Institute,
where he is Co-Director of the
Fellowship training program and
Clinical Associate Professor of
Orthopedic Surgery at the
University of Texas Southwestern
School of Medicine. He is the
Immediate Past-President of the
American Spinal Injury Association
(ASIA). Dr Zigler specializes in
degenerative spine surgery and
spinal arthroplasty and has
authored over 30 articles in peerreviewed scientific literature, has
written 14 textbook chapters on
topics related to spine surgery, and
has edited two textbooks, including
Spine Arthroplasty. He is the former
Chief of the Spinal Injury Service at
Rancho Los Amigos National
Rehabilitation Hospital in Downey
California. Dr Zigler received his MD
from the State University of New
York Health Science Center in
Syracuse, and completed an
orthopedic surgery residency at the
Mount Sinai Medical Center in New
York City and a Fellowship in spine
surgery at the Case Western
Reserve University School of
Medicine in Cleveland.
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Mechanical degeneration of the lumbar spine is a
normal part of the aging process. Low back pain as a
result of minor injuries, predominantly sprains and
strains, occur to almost everyone at some point in their
life. Repetitive soft tissue trauma or more significant
disruptive injuries, such as disc herniations (whether
they require surgical treatment or not), may serve to
accelerate the natural aging process.Although decreased
disc height and degeneration in the facet joints are
identified on lumbar spine radiographs of most middleaged people, only a small percentage of this population
develops significant enough pain and functional
restriction for surgical mechanical (non-neurologic)
intervention to be warranted.
The Degenerative
Process
Each segment of the lumbar spine is composed of an
intervertebral disc and paired posterior facet joints,
together with their soft tissue ligaments and capsules,
composing a functional spinal unit (FSU).
Degenerative changes in this unit, whether due to
normal senescence or as a result of injury, usually begin
in the anterior column within the disc nucleus.
The compressive component of the disc shock absorber
system is the nucleus, composed of macromolecules of
proteoglycans in a matrix of collagen and water. In the
young this is gelatinous and highly viscoelastic.With the
aging process the water content of the nucleus decreases
and the composition of the glycosoaminoglycan
protein sugars changes. The nucleus also becomes less
reactive to compression.
The annulus is a circular ligamentous structure that
acts to seal the disc space as well as oppose the
outwardly directed forces caused by nucleus
compression under axial load. The collagen fibril
structure on a microscopic level, combined with the
perpendicularly oriented layering of fiber bundles on
a macroscopic level, contribute to the hoop strength
of this structure. With natural aging or accelerated
aging due to trauma, the annulus becomes less elastic,
more brittle, and becomes prone to stretching,
cracking, and tearing as ligamentous tissue everywhere
else in the body does. When subjected to loading
stresses, the annular fibers may be partially injured,
causing pain directly (since these annular fibers are
innervated, unlike the nucleus) or indirectly by
reflexively triggering protective muscle spasm to
internally splint the damaged segment.
The last components of the FSU are the facet joints,
which are engineered to function in an optimal
co-existent position determined by the height of the
normal disc space. While the disc loses height the
facet joints no longer articulate as they were
intended. This can cause abnormal stresses within
these diarthrodial joints that have richly innervated
synovial linings and articular capsules.With the loss of
the mechanical turgor offered by plump discs, these
functionally subluxed joints and lax facet capsules
now allow broader segmental motion that further
stretches the capsules and ligaments and worsens the
articular surface mismatches, leading to accelerated
wear of the articular cartilage, osteophyte formation
where the capsular attachments are stressed and
inflamed by abnormal stresses, and more pain
generators from compensatory deep paravertebral
muscle spasm.
N o n - o p e r a t i v e Tr e a t m e n t
Most degenerative disease is well tolerated and
managed by the normal activity restriction of aging, as
well as by exercise and judicious use of over-thecounter (OTC) anti-inflammatory medication. For
pain that persists, physicians will recommend stronger
anti-inflammatory medication, muscle relaxants, and
appropriate pain medication. In addition, they will
generally prescribe some type of formal exercise-based
physical therapy for core muscle strengthening and
strengthening of the subcutaneous trunk musculature.
This conservative care plan successfully treats the
overwhelming majority of ‘back attacks’ as well as
making even chronic low back pain more tolerable.
O p e r a t i v e Tr e a t m e n t
Surgical treatment for functionally disabling mechanical
non-neurologic back pain (i.e. not sciatica or radicular
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Ar throplasty as the Next Evolution for Surgical Reconstruction of the Spine
pain caused by nerve root compression or irritation by
a herniated nucleus or a bone spur) has traditionally
been to identify the pain generator and remove it.This
usually required fusion of the segment or segments
involved because removal of the pain generator
(typically the disc) would render the segment unstable.
Fusion has been shown to be more effective than
conservative treatment in prospective randomised
studies, but is not problem-free.
Fusion
Attaining a surgical fusion has never been completely
reliable, despite the evolution of surgical technique.
Since the 1920s, surgeons have developed different ways
of fusing the spine utilizing different approaches
(posterior, posterolateral, anterior, and lateral), as well as
different means of internal fixation, the most recent
approach being biologic augmentation (bone
morphogenic proteins (BMPs)). Even though
radiographic fusion utilizing the newest techniques can
now be achieved in over 90% of patients, fusion is still a
less than optimal choice for reconstruction of the spinal
segment after removing the pain generator.
successful completion of a rehabilitation program,
patients may trade their deep aching discogenic or
facetogenic mechanical back pain for a different type of
muscular ache, loss of strength, and endurance in these
very important spinal stabilizers.
Successful fusion stiffens the functional spinal unit and
removes segmental motion. Since functional activities
such as putting on shoes, clipping toenails, and using the
toilet all still require extremes of spinal motion, adjacent
segments must mobilize even more to position the trunk
into the required positions. This is more of an issue in
multiple level fusions, and adjacent level breakdown has
been documented in post-fusion patients at greater
incidence than in non-fused surgical patients (e.g.
laminectomy patients). Breakdown in adjacent disc/facet
segments has also been observed in the sacroiliac and hip
joints downstream to a lumbosacral fusion.
For all these reasons, the bottom line, and the most
troubling outcome, is that fusion patients do not fare as
well functionally as their X-rays suggest. In the seminal
multicenter prospective randomized US Food and Drug
Administration (FDA) Investigational Device Exemption
The compressive component of the disc shock absorber system is
the nucleus, composed of macromolecules of proteoglycans in a
matrix of collagen and water.
Activity restriction and post-operative immobilization,
using braces and corsets, are typically prescribed for up
to three months after fusion, leaving patients who were
deconditioned prior to surgery (usually due to pain)
even more deconditioned once their fusion has healed
as a result of their post-operative immobilization. This
then necessitates a very lengthy rehabilitation process
that can take a number of months.
(IDE) studies undertaken for the BAK® Cages, the Ray
Threaded Fusion Cages, and the LT Cages® with BMP
(despite radiographic fusion rates above 90%), only twothirds of patients were satisfied or reattended work.1–3 This
disconnection between radiographic and clinical success is
a very sobering reality that made every spine surgeon
question whether fusion was the best surgical option for
the patient with disabling mechanical lower back pain.
Damage to the spinal muscles can occur with some
surgical approaches to the spine. Muscle tissue is
denervated and devascularized during the surgical
dissection and retraction to expose the spine; several
studies have shown that these muscles never completely
recover. Even with a perfectly healed fusion and
Ar throplasty—The Charité
Artificial Disc
Drs Karin Buttner-Janz and Kurt Schellnack developed
a lumbar artificial disc at the Charité Hospital in Berlin
and began patient implantations in the early 1980s.4
1. Burkus J K, Heim S E, Gornet M F, Zdeblick T A, “Is INFUSE bone graft superior to autograft bone? An integrated analysis
of clinical trials using the LT-CAGE lumbar tapered fusion device”, J. Spinal Disord.Tech. (2003): pp. 113–122.
2. Kuslich S D et al., “The Bagby and Kuslich method of lumbar interbody fusion”, Spine (1998);23: pp. 1,267–1,279.
3. Ray C D, “Threaded titanium cages for lumbar interbody fusions”, Spine (1997);22: pp. 667–680.
4. Buttner-Janz K, “History”, in Buttner-Janz K, Hochschuler S, McAfee P (eds), The Artificial Disc, Berlin: Springer (2003):
pp. 1–10.
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Figure 1: Inclusion of the L3-4 Disc
articles from Europe have been published, offering
generally good clinical results.5–7 A small number of
articles have noted complications such as core
dislocation, implant migration, and persistent pain.8
The FDA reviewed the data from a multicenter
prospective randomized trial comparing the Charité
disc with paired BAK cages and autologous iliac crest
bone graft for the treatment of functionally disabling
back pain from single-segment disease at L4-5 and
L5-S1. In October 2005, the FDA approved the
Charité device for those indications.
The US IDE data has been published and shows safety
and efficacy of the investigational device compared
with the control device within the parameters of the
FDA study.9 Two-year follow-up demonstrated a lower
complication rate than with the fusion patients. A
review of this data led to FDA authorization with the
proviso that surgeons be trained in this new technology
and that the patients be followed for additional period.
Charité implants in the US trial, sold in the US
subsequent to FDA approval, have smooth coated metal
endplates that do not allow for bony ingrowth. Reports
of isolated cases of late endplate migration requiring
revision are a cause for concern.8
They undertook design revisions and in 1987 the thirdgeneration SB Charité III device entered large-scale
implantation in Europe and other countries outside the
US. This is essentially the same implant currently
marketed by Johnson & Johnson/ DePuy Spine, who
acquired the device during the FDA IDE trials.
The Charité artificial disc is composed of two cobaltchrome endplates and a freely mobile and
unconstrained polyethylene core. The theory behind
the Charité disc is that the mobile poly core moves
anteriorly in segmental extension and posteriorly in
segmental flexion, mimicking the motion of the native
nucleus pulposus.This low-friction system theoretically
changes the center of rotation as the spine moves.
Over 15,000 patients worldwide have had Charité
discs implanted, dating back to 1985. Only a few
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Since its approval, Charité disc usage in the US has been
less than was anticipated due to a variety of factors.
Insurance carriers have been slow to authorize
implantation and many patients remain faced with the
realities of accepting a fusion or paying for the surgery
themselves. Surgeon acceptance has been lower than
anticipated. Although over 2,000 surgeons were trained
by Johnson & Johnson, only a fraction of those surgeons
have performed the procedure in the one year following
FDA approval. Concerns regarding instrumentation and
surgical technique, as well as presentation of data
suggesting that suboptimal positioning may result in
poorer clinical results, may also have contributed to
usage below earlier forecast levels.10
Ar throplasty—ProDisc
The ProDisc is a semi-constrained implant that has a
polyethylene dome fixed to the inferior cobalt-
5. Lemaire J P, Skalli W, Lavaste F et al., “Intervertebral disc prosthesis. Results and prospects for the year 2000”, Clin. Orthop.
(1997);337: pp. 64–76.
6. Lemaire J P, Carrier H, Ali E S et al., “Clinical and radiological outcomes with the Charite´TM Artificial Disc: A 10-year
minimum follow-up”, J. Spinal Disord.Tech. (2005);18: pp. 353–359.
7. Zeegers W S, Bohnen L M L J, Laaper M,Verhaegen M J A,“Artificial disc replacement with the modular type SB Charité III:
2-year results in 50 prospectively studied patients”, Eur. Spine J. (1999);8: pp. 210–217.
8. van Ooij A, Oner F C,Verbout A J, “Complications of artificial disc replacement: a report of 27 patients with the SB Charite
disc”, J. Spinal Disord.Tech. (2003);16: pp. 369–383.
9. Blumenthal S L, McAfee P C, Guyer R D et al.,“A prospective, randomized, multi-center FDA IDE study of lumbar total disc
replacement with the CHARITÉ(tm) artificial disc vs. lumbar fusion: Part I - Evaluation of clinical outcomes”, Spine (2005);30:
pp. 1,565–1,575.
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NORTH AMERICAN
SPINE
SOCIETY
.
.
E D U C AT I O N
RESEARCH
ADVOCACY
The North American Spine Society is a multidisciplinary medical
organization that advances quality spine care through
education, research and advocacy.
Benefits of Membership
Currently, over 4,000 physicians and surgeons, researchers, physician
assistants, physical therapists, nurse practitioners and other health
professionals in 22 spine-related specialties are members of NASS.
NASS members are entitled to special, discounted registration fees
for all NASS-sponsored educational programs; receive The Spine
Journal, a multidisciplinary peer-reviewed publication, and SpineLine,
our bimonthly socioeconomic magazine; enjoy a discount on all
NASS publications and patient education materials; can participate
in the National Association of Spine Specialists, our advocacy arm;
and benefit from a number of other member services. Download a
membership application form at www.spine.org/membership.cfm
Continuing Medical Education
As an ACCME-accredited organization, NASS provides top-quality,
relevant continuing medical education in the latest noninvasive
techniques, surgical procedures, pharmaceutical and device
innovations for the care of spine patients, as well as the latest
research in basic/applied clinical science and practice management
methods. NASS’ 21st Annual Meeting will be held September 26-30,
2006, in Seattle, Washington. Increase your knowledge of spine care,
learn innovative techniques and network with peers.
Visit www.spine.org for a complete list of courses and dates.
Patient Education
NASS offers informative brochures and handouts for patients on
a broad range of topics including spine health maintenance and
specific diseases such as herniated disc and spondylolisthesis.
These 8-16 page full-color brochures in easy-to-understand
language inform your patients about their condition and the
available treatment options, both medical and surgical.The fullcolor handouts focus on understanding spine anatomy and the
prevention of back pain. A list of titles and order form can be
downloaded from http://www.spine.org/forms/patedordfm.pdf
The North American Spine Society
22 Calendar Ct., 2nd Floor, LaGrange, IL, 60525
(708) 588-8080 or toll-free (877) SPINE-DR
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chrome-molybdenum (Co-Cr-Mo) metal endplate.
Theoretically, this internal resistance to translational
shear force should decrease force on the facets
and prevent degeneration in those joints more than
the Charité disc; however, this has yet to be
clinically proven.
The ProDisc was invented by Dr Thierry Marnay, a
French orthopedic spinal surgeon, in the late 1980s.
Dr Marnay implanted the device into 64 of his
patients in the early 1990s and then showed
remarkable academic restraint by stopping
implantation so that he could follow his patients’
progress. Although three of these patients had died of
natural causes, 95% of the living 61 patients were
tracked down and evaluated at the seven- to 11-year
follow-up. All the devices were functional and none
had required explantation. Over 92% of the patients
there were one- and two-level study arms (see Figure
1) and the L3-4 disc was included.
National multicenter data from the ProDisc study is
not available because the FDA has not granted
approval for the device to date, although it is
anticipated by the first quarter of 2006. However, the
author has reported the combined results at the two
largest contributing sites. The data for 181 patients
with two- to three-year follow-up shows that patients
with arthroplasty have better pain scores, Oswestry
functional scores, and satisfaction scores than the
randomized fusion control patients.12 Additionally, a
higher percentage of the ProDisc patients (as opposed
to the fusion patients) would repeat the surgery.
In a separate study of 80 single-level and 48 two-level
ProDisc patients at the Texas Back Institute study site,
Most degenerative disease is well tolerated and managed by
the normal activity restriction of aging, as well as by exercise
and judicious use of over-the-counter (OTC) antiinflammatory medication.
were satisfied or very satisfied with their implants and
would have the surgery again.11
On the strength of the long-term follow-up data, the
FDA allowed testing of an updated ProDisc implant
(single keel, Co-Cr endplates, modular polyethylene
component) to begin IDE testing in the US. On
October 3 2001 the author implanted the first
ProDisc in the US at the Texas Back Institute.
A multicenter trial (19 investigative sites) prospectively
randomized the ProDisc to a 360° fusion with pedicle
screws. The ProDisc trial was different to the Charité
study not only in its choice of control but also because
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no significant differences were observed between
these two patient populations in terms of pain,
function, or patient satisfaction scores.13 In other
words, patients who underwent two-level arthroplasty
essentially had the same results as those who only had
one level replaced.
Ar throplasty—Maverick
Maverick is a two-piece metal-on-metal implant in the
data-collection phase of an IDE trial comparing it in
prospective randomized fashion with anterior fusion
with LT cages and InFuse in patients with single-level
disc disease. Maverick’s purported advantages include a
10. McAfee P C, Cunningham B, Holtsapple G et al., “A prospective, randomized, multi-center FDA IDE study of the
CHARITÉ™ Artificial Disc: A radiographic outcomes analysis, correlation of surgical technique accuracy with clinical outcomes,
and evaluation of the learning curve”, Spine (2005);30: pp. 1,576–1,583.
11. Tropiano P, Huang R C, Girardi F P et al., “Lumbar total disc replacement. Seven to eleven-year follow-up”, J. Bone Joint
Surg. Am. (2005);87: pp. 490–496.
12. Zigler J E, Delamarter R B, Ohnmeiss D D et al., “Lumbar total disc replacement: A 2 to 3 year report from 2 centers in the
United States clinical trial for the ProDisc-II prosthesis”, Spine Arthroplasty Society (May 2005), New York.
13. Zigler J E, Sachs B L, Rashbaum R F, Ohnmeiss D D,“Two-level total disc replacement with ProDisc: Results and comparison
to one-level cases”, Spine Arthroplasty Society (May 2005), New York.
14. Le Huec J C, Mathews H, Basso Y et al.,“Clinical results of Maverick lumbar total disc replacement:Two-year prospective followup”, Orthop. Clin. North Am. (2005);36: pp. 315–322.
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posterior fixed center of rotation to theoretically protect
the facets and metal-on-metal bearing surfaces for
improved wear characteristics. However, the issues of
particulate debris and the systemic absorption of metal
ions shed from the articulating surfaces are still uncertain.
Early results from European sites indicate good clinical
outcomes with the Maverick implant,14 although
extensive data is not readily available. Maverick uses a
central keel for fixation, but, unlike the ProDisc’s short
keels, Maverick’s are much taller and probably preclude
adjacent level usage in present form. Like ProDisc, the
Maverick implant is coated to promote bony ingrowth.
Ar throplasty—Flexicore
Flexicore is a constrained one-piece metal-on-metal
implant that, like Maverick, is in the data-collection phase
of its FDA trial. It was randomized to a 360° fusion for
single-level disease at L4-5 or L5-S1. Little clinical
management, and in many of those patients a discrete
pain generator can be identified within the disc. In
those circumstances, surgery is often recommended and
is even requested by the patient.
Surgeons have become more effective at achieving a
radiographic fusion, although functional outcomes lag
behind; in other words, a solid fusion alone does not
guarantee a good clinical outcome. Factors responsible for
this may include muscle damage from surgery and the
abnormal spinal mechanics that result from fusion,
causing adjacent segment overuse and possibly early
transitional degeneration. Even with those factors, clinical
outcomes in fusion patients are still better than continued
non-operative manage-ment once it has failed.
Despite European experience with lumbar arthroplasty
dating back 20 years, there is no scientifically
acceptable follow-up data on these early patients.
Surgical treatment for functionally disabling mechanical nonneurologic back pain…has traditionally been to identify the pain
generator and remove it.
information is available except for reports of interim data
involving small cohorts of single-center patient data.15
Flexicore has the technical advantages of allowing
anterolateral insertion, as well as allowing the surgeon to
reposition the implant within the disc space if the surgeon
is not happy with its position after initial placement.
Ar throplasty—Kineflex
Kineflex is a keeled implant with a free-floating metal
core. It began an IDE trial in early 2005 and is the first
artificial disc replacement (ADR) randomized not to
fusion but to another ADR (Charité). No US clinical
data is available yet, but good results have been shown
in studies outside the US.16
Conclusions
The non-surgical treatment for disabling mechanical
disc disease is effective for a majority of patients.
However, there are some people who have persistent
disabling pain despite appropriate conservative care
Several carefully monitored prospectively randomized
studies comparing ADR with fusion are under way in
the US and one study has already been published with
two-year follow-up data.These patient cohorts need to
be followed for 10 to 20 years to determine whether
arthroplasty will deliver on its potential as the better
option for spinal reconstruction after removal of the
pain generator is to be determined.
What is encouraging to date are very good early results
indicating that patients progress as well, if not
somewhat better, with ADR than with fusion. Longerterm questions of facet protection and adjacent-level
protection from the transitional syndrome will need
more time; however, the patient cohorts involved in
the FDA IDE studies will be well selected populations
to study. Their pre-operative baseline data as well as
multiple data points (radiographs and clinical
examinations) will be available for comparison5,10,15,20
and even longer-year follow-ups by students. Only
then will questions be answered with scientific
evidence instead of opinion. ■
15. Miz G, “FlexiCore lumbar disc arthroplasty: A preliminary report”, Spine Arthroplasty Society (May 2005), New York.
16. Hahnle U R,Weinberg I R, de Villiers M,“One to two year results with Kineflex (Centurion) lumbar disc”, Spine Arthroplasty
Society (May 2005), New York.
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