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Artificial Cervical Disc Replacement

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					 New and Emerging
Techniques - Surgical

      Procedure Brief

   Artificial Cervical
   Disc Replacement

          October 2001




         New and Emerging Techniques – Surgical

     Procedure briefs are for informative purposes only
           and should be used with due caution.
New and Emerging Techniques – Surgical                              Artificial Cervical Disc Replacement



                                     Procedure Brief Summary

                               Artificial Cervical Disc Replacement

    •   Following the success of artificial prostheses for hip and knee joints, attention has been
        focused on the development of intervertebral disc prostheses.

    •   Several lumbar disc prostheses are available, but prostheses for the cervical spine pose
        more complex biomechanical considerations.

    •   Cervical disc technologies reported in this brief include
                   • The Bristol (Cummins) Disc
                       A ‘ball and socket’ device constructed of stainless steel.
                   • The Bryan Cervical Disc System
                       A composite artificial disc with a low friction, wear resistant elastic
                       nucleus placed between two anatomically shaped titanium end-plates.

    •   Suitable patients include those patients where surgical intervention is indicated due to
        their chronic symptoms resulting from cervical disc spondylosis.

    •   Treatment alternatives include discectomy alone, or discectomy and fusion.

    •   Drawbacks from current treatments include;
                 • Loss of cervical mobility
                 • Risk of increased load and therefore increased degeneration of adjacent
                     spinal levels
                 • Pseudoarthritis
                 • Increased incidence of postoperative interscapular pain
                 • Donor site complication, when bone grafts are used

    •   Current research evidence suggests that patients receiving the Bryan Cervical Disc
        System have and “excellent” outcome based on a neurological assessment and Bristol
        (Cummins) disc was protective against undesirable motion that is seen with fusion, as
        well as maintaining motion at the site of the prosthesis.

    •   There have been reports of adverse events for both the Bryan Cervical Disc System and
        the Bristol (Cummins) Disc, including;
                    • Postoperative neck pain, failure of intended mobility, hoarseness (Bryan
                       Cervical Disc System)
                    • Screw breakage and partial screw pullouts (Bristol (Cummins) Disc)

    •   No cost data is presently available for Australia.

                                       NET-S Classification
    Cervical disc prostheses are classified as an emerging technique, and are currently in the early
    phase of introduction into Australian health care services.


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New and Emerging Techniques – Surgical                                        Artificial Cervical Disc Replacement



                                                  Background

Technological advances made in large joint reconstructive devices and biomaterials have
revolutionised the treatment of all types of degenerative joint disease. Following the success of
total joint arthroplasties for the hip or knee joints, attention has more recently focussed on the
successful development of intervertebral disc prostheses. Prostheses developed to replace lumbar
intervertebral discs have been attempted first; more than 40 years ago Alfred Nachemson1
implanted stainless steel balls to replace lumbar intervertebral disc spaces in over 100 patients.
Since then several lumbar disc prostheses have been developed such as the Link SB Charité, the
Acromed Acroflex disc as well as several custom designed discs by Kostuik2, Lee3 and Kadoya.4

The cervical spine, however, poses much more complex biomechanical considerations, hence the
more belated development of a suitable cervical disc prosthesis. Recent advances in both the
biomechanical knowledge of the cervical spine and in the long-term use of biomaterials have
greatly assisted the development of several cervical disc replacement systems. Successful
cervical disc prostheses have to satisfy a number of design prerequisites. Proper intervertebral
spacing has to be maintained whilst allowing for normal anatomical motion but constraining all
other motion in any inappropriate, non-anatomical degrees of freedom. Both ligamentous and
facet joint integrity need to be maintained for stability of the functional spinal unit and the
prosthesis must also continue to provide shock absorption. As the expected treatment population
could involve relatively younger patients with cervical disc injury due to trauma, or older patients
with degenerative disc disease, all components and the implant construct itself must have an
estimated average life expectancy of at least 35 to 50 years.

                                                The Technology

There are several models of cervical disc prostheses currently in development. Outlined below is
a brief overview for each of the prosthesis.

The Bristol (Cummins) Disc
The Bristol disc pictured below (Figure 1) is a “ball and socket” device constructed of stainless
steel that mimics the anatomical range of motion of the cervical discs.




                                      Figure 1: The Bristol Disc (X-ray)i

The Bryan Cervical Disc System (Spinal Dynamics/Medtronic Sofamor Danek)

i
    Figure 1 from: http://www.spineuniverse.com/technology/dp_040501traynelis_artdisc_future.html


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New and Emerging Techniques – Surgical                                         Artificial Cervical Disc Replacement


The Bryan cervical disc (Figure 2) is a composite artificial disc with a low friction, wear resistant
elastic nucleus placed between two anatomically shaped titanium end-plates. The end-plates are
dome shaped with polished concave spherical articular surfaces. After implantation, the pre-
existing facets, annulus fibrosus, ligamentous and muscular soft tissues remain intact to define
the disc kinematics and allow for the coupled vertebral motions characteristic of the cervical
spine. Long-term fixation of the implant is achieved via bone ingrowth into the porous coated
surface (see Figure 2). The Bryan cervical disc replacement system necessitates a cervical
discectomy using the standard anterior approach. However, in this case, the resultant defect left
after discectomy is replaced by the disc prosthesis.




                                   Figure 2: Bryan Cervical Disc Prosthesisii

Other Reported Cervical Disc Prostheses
Hydraulic artificial discs have also been developed which possess a gel-like core with a tightly
woven polyethylene overcoat.5 Before implanting, the pellet-shaped hydro-gel core is
compressed and dehydrated to minimise its size. Once implanted, the outer woven cover allows
fluid to pass through to the core that subsequently absorbs the fluid and expands. Whether these
hydraulic artificial discs have a cervical disc application is unknown at this time.

A group of German neurosurgeons from the Bethesda-Hospital in Wuppertal have also developed
a titanium device specifically for use in cervical disc replacement although the last published
references to this device appear to be in 1995.6

The development of an artificial cervical disc has also been of interest to Japanese surgeons. In
the early 1990’s, Tsuji et al. published two articles7,8 reporting on a cervical intervertebral disc
replacement made of a ceramic material although the primary application, in these cases, appears
to be specifically for spinal tumours which necessitate the removal of a cervical disc.

After this apparent surge in cervical disc prosthetic development in the early 1990s, it is currently
unclear whether any of these other cervical disc prostheses are currently in use




ii
     Figure 2 from: http://www.spineuniverse.com/technology/dp_040501traynelis_artdisc_future.html


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New and Emerging Techniques – Surgical                              Artificial Cervical Disc Replacement



                                          Patient Group

The group of patients most suitable for cervical disc prosthetic replacement are those patients
where surgical intervention is indicated due to their chronic symptoms resulting from cervical
spondylosis. Cervical spondylosis can produce four types of clinical manifestations: intrinsic
neck pain with local referred pain, radiculopathy with signs and symptoms of nerve root
compression; myelopathy with signs and symptoms of spinal cord compression and
myeloradiculopathy which presents as a combination of symptoms consistent with both nerve
root and spinal cord compression. Aetiology of the neural compression is either an acute disc
herniation or disc space narrowing and osteophyte formation consistent with degenerative disease
or a trauma such as a whiplash injury.

Cervical radiculopathy is the most common indication for a patient to be considered for operative
intervention. It is more common in the fourth and fifth decades of life with males presenting
more frequently than females at a ratio of four to one.9 The lower cervical spine is the primary
site of involvement. C5-C6 and C6-C7 are involved in nerve root compression in 75% of all
reported cases. The primary indication for surgical intervention is chronic pain in a dermatomal
distribution, motor weakness or clinical findings upon diagnostic MRI testing.

                               Current Treatment and Alternatives

Two current surgical treatment modalities are available. They can be generally categorised as
either a cervical discectomy that is performed alone or a cervical discectomy procedure that is
followed by fusion. The fusion can be achieved in a number of ways using either an autologous
or non-autologous bone graft. This bone grafting can be further augmented by internal fixation
such as cervical plates or fusion cages for added stability. This type of anterior disc excision and
stabilisation was popularised in the 1950s by Robinson and Smith10, Cloward 11 and Bailey and
Bagley.12 Modifications have been made over the subsequent years to the basic surgical
procedure with changes in operating room orientation, method of distraction of the involved disc
space, graft or spacer insertion and postoperative management. More recently, biomechanical
spacers made either from titanium or carbon fibre (Novus CSR-C, Novus CT (Ti) and
Cornerstone-SR, Sofamor-Danek, Memphis, USA) have also been tried as bone graft substitutes.
A Cochrane Review assessing the efficacy of current surgical techniques for cervical
radiculopathy is currently being undertaken by Fouyas et al.13

                              Limitations of the Current Techniques

While it is reported that up to 70% of patients get a good or excellent result with the Robinson
Smith and Cloward techniques9 with most patients experiencing relief from symptoms, a number
of limitations of the current surgical techniques have been clearly identified. One of the key
limitations of these surgical techniques is that although surgical fusion stabilises the vertebrae,
thus relieving pain and other symptomatology of disc degeneration, it also immobilises that
portion of the cervical spine, resulting in a subsequent loss of cervical mobility for the patient.
There is also mounting evidence that discectomy with subsequent fusion with either
autologous/non-autologous bone grafting leads to an increased load on the adjacent spinal levels.


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New and Emerging Techniques – Surgical                             Artificial Cervical Disc Replacement


This increased load, in turn, can lead to an accelerated degeneration at the adjacent levels. A
study recently published by Goffin14 reported that 92% of patients in their sample (n=120)
demonstrated increased degeneration at superior and/or inferior disc levels as judged by an
independent radiologist. In this series, radiological degeneration was often accompanied by a
clinical deterioration as well. The patterns of degeneration were similar for both the trauma and
non-trauma (degeneration) patients in the sample that suggests that the fusion itself was the
primary cause of the increase in cervical spine degenerative pathology observed. Hilibrand15 has
reported a re-operation rate on adjacent levels of 2.9% per level per year, with 30% of patients
requiring a re-operation at an adjacent disc level after ten years.

Other reported complications of the standard surgical treatment include pseudoarthrosis and an
increased incidence of postoperative interscapular pain. It has been postulated that this pain is
caused by an increased incidence of disc space collapse or subsidence of the spinal construct. In
cases where the discectomy is subsequently followed by bone grafting, further problems can arise
with donor site complications such as infection, pelvic fracture, meralgia paresthetica and chronic
pain. These donor site complications have been reported to occur in up to 20% of cases.16 Recent
attempts to eliminate donor site and subsequent graft complications through the use of graft
substitutes such as methyl-methacrylate or bone morphogenic protein (using either BMP-2 or
BMP-7) have not been successful to date in humans.

                                    Current Research Evidence

Current European Trials
Since July 2000, a multi-centre, prospective, randomised European trial using the Bryan cervical
disc prosthesis has accrued a total of 86 patients. This study involves nine investigators at seven
different European centres. All eligible patients had cervical disc herniation accompanied by
either radiculopathy or myelopathy that had not responded to conventional treatment modalities.
All radiculopathy patients had intractable pain and all myelopathy patients had intractable
paraesthesia preoperatively. Each patient’s aetiology was demonstrated both on plain film and CT
scan. Outcome measures were a neurological assessment (Using Odom’s classification system of
“excellent”, “good” or “fair”) and patient based pain and function assessments. A radiographic
measurement of postoperative range of motion was also made at six months and one year.

Preliminary results are currently available for 48 patients at six months postoperatively and 23
patients at one year postoperatively. All 71 of these patients had disc replacement involving
levels from C4 to C7. The age range of the sample was between 27 to 71 years of age.

At six months, scores of “excellent”, “good” or “fair” could be assigned to 43 of the 48 patients.
Thirty-four of these 43 patients were classified as having an excellent clinical result. Of the 23
patients who had follow-up of at least one year, 21 were classified as having an excellent result.
Radiographic follow-up data as assessed by an independent radiologist could be reported on for
44 patients at six months and 17 patients at one year. At six months, 40 of the 44 patients
demonstrated flexion/extension range of motion equal to or greater than two degrees. At one
year, 15 of the 17 reported patients demonstrated a flexion/extension range of motion equal to or
greater than two degrees.



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New and Emerging Techniques – Surgical                               Artificial Cervical Disc Replacement


Early radiographic analysis has measured no subsidence in any implant examined and no
anterior-posterior device migration greater than 3 mm. However, one case of a cephalic shell
migration has been reported consisting of a 3 mm displacement in an anterior direction. This
appears to have been caused by implant failure due to faulty milling of the end-plate in the
manufacturing phase.

This European multi-centre group is also undertaking two other studies investigating the Bryan
cervical disc prosthesis. One involves the biomechanical study of the Bryan disc in collaboration
with a US group, and the second trial will examine multi-level cervical implants.

A British trial involving two cohorts of patients who received either an artificial Bristol joint/disc
(n=12) or an autologous bone graft fusion (n=13) was reported in 2000 by Wigfield17 at the
Congress of Neurosurgeons meeting in San Antonio, Texas. The objective of this study was to
compare the Bristol disc against interbody fusion with respect to radiographic changes in
angulation occurring at adjacent levels. In this study, the fusion group showed a significant (p<
0.001, Fisher’s exact test) increase in adjacent level movement at their one-year follow-up when
compared to the Bristol artificial joint group. The main increase in movement occurred at discs
that were preoperatively regarded as normal. These results suggest that the fusion resulted in a
greater degree of motion at adjacent spinal levels while the Bristol artificial joint was more
protective against this undesirable motion while maintaining motion at the site of the prosthesis
itself.

Current Australian Trials
There are also two Australian pilot investigations underway. One involves the Bryan cervical disc
system while the second study is investigating the Bristol joint/disc.

Adverse Events Reported
Cummins et al.18, (Bristol/Cummins disc) reported a series of 20 patients who were followed for
an average of 2.4 years. The first five patients had a single stainless steel screw placed in the
anterior joint; in this group there were three partial screw pullouts, one broken screw and one
joint subluxation (partial dislocation) causing moderate, persistent dysphagia (difficulty in
swallowing). The next 15 patients in the series had titanium A-O locking screws to affix the joint
anteriorly. Of this group, there were two partial screw pullouts, one broken screw, one transient
hemiparesis (muscle weakness on one side of the body) due to spinal cord injury whilst drilling,
three cases of persistent mild dysphagia and one joint that was loose and subsequently removed
(manufacturing error) and persistent pain. As can be seen, complications occurred in a significant
number of these cases.18

The ongoing European multi-centre trial for the Bryan cervical disc has also reported adverse
events from the other centres in their preliminary report. There has been one incidence of minor
intraoperative bleeding from an anchor hole following removal of an anchor (the anchor is placed
in the vertebral body to facilitate the placement of the device). However, in this event, the
bleeding was successfully resolved with bone wax, with no need for blood transfusion. Two other
postoperative events reportedly occurred during a case where the wrong cervical level was
operated on. This patient developed unresolved pain following the initial surgery. A follow-up
revision of the implant at the targeted level was immediately undertaken in this case. One
reported incident of dysphonia (hoarseness) was also reported which resolved postoperatively.


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New and Emerging Techniques – Surgical                                        Artificial Cervical Disc Replacement



                                                      Cost

With respect to the Bryan cervical disc system, Medtronic Sofamor Danek is currently in the
process of costing this particular item for the surgical retail market. Once available, this price will
be posted here. The current price of the Bristol disc, which is also distributed by Medtronic
Sofamor Danek, is also currently unavailable.

                                                  Prevalence

Cervical degenerative disease is an almost universal concomitant of human aging. Early studies
reported that over half of the middle-aged population has radiological and/or pathological
evidence of cervical spondylosis.19-21 Degenerative disease of the cervical spine is the most
common cause of cervical cord and nerve root dysfunction, and the disease progresses with age.
One study has reported that radiographic changes of cervical spondylosis are found in 75% of
patients older than 60 years of age whilst an earlier study reported that 90% of the male and
female patients in their sample over the age of 60 had radiographic evidence of cervical
degeneration.22 Recently, it has been reported that over 200,000 patients per year, worldwide,
undergo surgical treatment for damaged cervical discs and that approximately 125,000 cervical
spine fusions are performed in the United States alone each year.17

                                                   Summary

The current available treatments produce good clinical results in the majority of patients. In use
since the 1950s, these surgical modalities have undergone modifications over the years to
improve both surgical technique and patient outcome. However, a few major limitations which
have been difficult to resolve still remain, such as the resultant immobility of the cervical spine
segment post-fusion, the occurrence of increased degeneration in adjacent spinal levels
necessitating further surgery in 30% of cases after 10 years, risk of pseudoarthrosis and the
problems that commonly occur at donor sites after bone grafting procedures. With the
overwhelming success of prostheses developed for other joints prone to degenerative changes
such as the hip or knee, it seems natural that on-going efforts should be made to develop a
successful cervical disc replacement as well. Some of the proposed cervical disc systems appear
to be in a more highly advanced stage than others and efforts are currently being made to
investigate their use using human clinical trials. Some adverse events have already been reported
with at least two of the cervical disc systems currently available. These events may necessitate a
design reappraisal before the widespread introduction and use of these cervical disc systems.
Cervical disc prostheses are classified as an emerging technique, and are currently in the early
phase of introduction into Australian health care services.

                                                  References

  1. Nachemson AL. Challenge of the artificial disc. In: Weinstein JN, editor. Clinical Efficacy and outcome in the
     diagnosis and treatment of low back pain. New York: Raven Press; 1992.




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New and Emerging Techniques – Surgical                                          Artificial Cervical Disc Replacement


  2. Kostuik J. Intervertebral disc replacement-Experimental study. Clinical Orthopaedics & Related Research
     1997; 337:27-41.

  3. Lee C, Langrana N, Parsons J et al. Development of a prosthetic intervertebral disc. Spine 1991; 16(6
     (Suppl)):S253-S255.

  4. Kadoya K, Kotani Y, Abumi K et al. Biomechanical and morphologic evaluation of a three dimensional fabric
     sheep artificial intervertebral disc: In vitro and in vivo analysis. Spine 2001; 26(14):1562-1569.

  5. Traynelis V, Haid R Jr. Spinal Disc Replacement: The Development of Artificial Discs. Spine Universe . 10-
     10-2001.

  6. Kaden B, Schramm J, Fuhrmann G, Hoffmann CH. Titanium intervertebral disc and instrumentation for
     fusion in anterior cervical discectomy. Neurosurgical Review 1995; 18(1):25-29.

  7. Tsuji H, Itoh T, Yamada H et al. Artificial ceramic intervertebral disc replacement in cervical disc lesion.
     Journal of the Western Pacific Orthopaedic Association 1990; 27(1):101-106.

  8. Matsui H, Tatezaki S, Tsuji H. Ceramic vertebral body replacement for metastatic spine tumors. Journal of
     Spinal Disorders 1994; 7(3):248-254.

  9. Whitecloud TS, III. Modern alternatives and techniques for one-level discectomy and fusion. [Review] [27
     refs]. Clinical Orthopaedics & Related Research 1999; (359):67-76.

 10. Robinson RA, Smith GW. Anterolateral cervical disc removal and interbody fusion for cervical disc
     syndrome. Bulletin: Johns Hopkins Hospital 1955; 96:223-224.

 11. Cloward RB. The anterior approach for removal of ruptured cervical discs. Journal of Neurosurgery 1958;
     15:602-617.

 12. Bailey RW, Bagley CE. Stabilisation of the cervical spine by anterior fusion. Journal of Bone and Joint
     Surgery (American volume) 1960; 42A(565):624.

 13. Fouyas IP, Statham PFX, Sandercock PAG, Lynch C. Surgery for cervical radiculopathy (Cochrane Review).
     The Cochrane Library, Oxford 2001;(2).

 14. Goffin J, Geusens E, Vantomme N, Quintens E, Waerzeggers Y, Depreitiere B et al. Long-term Follow-up
     After Interbody Fusion of the Cervical Spine. [28th edition], 1-2. 2001. Charleston, South Carolina. Annual
     Meeting of the Cervical Spine Research Society.

 15. Hilibrand A, Yoo J, Carlson G. The success of anterior cervical arthrodesis adjacent to a previous fusion.
     Spine 1997; 22:1574-1579.

 16. Brown C, Eismont F. Complications in spinal fusion. Orthopedic Clinics of North America 1998; 29:679-699.

 17. Wigfield CC, Nelson RJ. Nonautologous interbody fusion materials in cervical spine surgery: how strong is
     the evidence to justify their use? Spine 2001; 26(6):687-694.

 18. Cummins BH, Robertson JT, Gill SG. Surgical Experience with an implanted artificial cervical joint. Journal
     of Neurosurgery 1998; 88:943-948.

 19. Hughes JT, Brownell B. Necropsy observations on the spinal cord in cervical spondylosis. Rivista di
     Patiologia Nervosa e Mentale 1965; 86:196-204.




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New and Emerging Techniques – Surgical                                       Artificial Cervical Disc Replacement


 20. Irvine DH, Foster JB, Newell DJ, Klukvin RN. Prevalence of cervical spondylosis in a general practice.
     Lancet 1965; 2:1089-1092.

 21. Pallis C, Jones AM, Spillane JD. Cervical Spondylosis. Brain 1954; 77:274-289.

 22. Friedenberg ZB, Miller WT. Degenerative disc disease of the cervical spine: A comparative study of
     asymptomatic and symptomatic patients. Journal of Bone and Joint Surgery (American volume) 1963;
     45A:1171-1178.




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