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Artificial Disc Replacement-Evolutionary Treatment for Degenerative Disc Disease

Posted on: Wednesday, 17 August 2005, 03:00 CDT

ABSTRACT

* BACK PAIN IS A COMMON PROBLEM that affects the majority of people at some point in their lives. Most back pain is not serious, but back pain caused by injury and aging can result in chronic pain that can last months, years, or indefinitely.

* ARTHRODESIS (ie, spinal fusion) has been the treatment of choice for symptomatic degenerative disc disease that has not responded to conservative treatment modalities. Artificial disc replacement is a more recent option that preserves spinal motion but also recreates the natural function of the disc.

* THE HISTORY OF ARTIFICIAL DISC replacement surgery, preoperative preparation, the surgical procedure, and postoperative recovery are discussed. AORN J 82 (August 2005) 192-206.

Back pain is a common health problem that affects the majority of people at some point in their lives.1,2 Most back pain is not serious, and it may be the result of poor posture, improper body mechanics, or overexertion. Back pain caused by injury and aging, however, can result in chronic pain that lasts an extended or indefinite amount of time (eg, months to years).1

About 50% of people older than 40 years of age have degenerative disc disease (DDD), which is a condition similar to osteoarthritis.1 Many patients with DDD do not have symptoms or pain,1 but for others, chronic debilitating pain can become a lifealtering condition that affects their activities of daily living and quality of life. In addition,

the socioeconomic and psychosocial impact of this disease can have far reaching effects. The treatment of this disease entity in the United States is expected to exceed $60 billion annually in health care costs. The indirect economic losses associated with lost wages and decreased productivity are staggering.1

Arthrodesis (ie, spinal fusion) has been the treatment of choice for symptomatic DDD that has not responded to conservative treatment modalities (eg, physical therapy medication), but spinal fusions may fail if the bone does not heal or "fuse" correctly. Furthermore, immobilization of the fused spinal segment can cause increased stress at adjacent segment levels, potentially furthering the DDD process.1,3-9 Although adjacent segment disease still is considered theoretical, several studies have reported that it occurs at a rate of 36.1% within 10 years of the initial fusion.2,10 Other studies involving DDD of the cervical spine support this finding.3-5 These factors have led spine surgeons to search for disc replacement methods that not only will preserve spinal motion but also will recreate the natural function of the intervertebral disc (IVD). Artificial disc replacement modalities may be the answer.

ANATOMY AND PHYSIOLOGY OF THE SPINE

The spine is a biomechanical marvel that allows flexion, extension, and a wide range of motion for the body. The spine naturally curves at the cervical, thoracic, and lumbar regions. Within the anteroposterior plane, there are four normal curvatures to the adult spine from superior to inferior. The convexity of the cervical and lumbar portions of the spine face anteriorly; whereas, the convexity of the thoracic and sacral portions of the spine face posteriorly. Most injuries occur at the lower lumbar level because the majority of the axial weight of the torso is distributed toward the pelvis. The vertebral body becomes larger toward the sacrum where more weight is carried. Facet joints on the posterior aspect of the spinal column distribute approximately 20% of the axial force of the torso and can be a significant source of pain in the lower back in the presence of a disease process such as facet joint syndrome (ie, a condition similar to arthritis with pain that does not involve root compression or neurological sequelae)." It often is difficult, however, to distinguish facet joint pain from pain caused by the symptoms of DDD.

Intervertebral discs are fibrocartilaginous elastic cushions (ie, shock absorbers) located between each vertebral body (Figure 1). They have high water content and a glycoprotein component called the nucleus pulposus. The IVD gives the intervertebral space height and stability. A person usually is taller in the morning than in the evening because of compression of discs' water content throughout the day. The annulus fibrous (ie, an outer ring of collagen fibers) surrounds the IVD. Tears in the annulus and subsequent ligament stretching can cause significant back pain because there are many nerve endings in these structures. Nerve roots in the spinal cord carry sensory messages from the brain and end in a bundle at the base of the spine called the cauda equina.12,13

PATHOPHYSIOLOGY OF DEGENERATIVE DISC DISEASE

Degenerative disc disease occurs when an IVD becomes worn out because of aging or as a result of cumulative damage or trauma. With DDD, the disc does not correctly cushion the vertebrae and distribute body weight. Discs can wear out, tear, bulge outward, or rupture through the annulus causing pressure on the nerve roots that results in nerve impingement, inflammation, and pain. Nerve impingement can cause numbness and muscle weakness of extremities, sciatica, and even bowel or bladder problems. If this is left untreated, permanent nerve damage may occur. As discs wear down, bone spurs and osteophytes form on the vertebrae in a condition similar to osteoarthritis. Discogenic back pain generally is mechanical in nature and is exacerbated by sitting, lifting, standing, jumping, or any activity that causes rotation of the spine.13,14

Figure 1 Normal anatomy of the spine depicting a normal intervertebral disc.

CONSERVATIVE TREATMENT FOR BACK PAIN AND DEGENERATiVE DISC DISEASE

Patients are given a conservative course of treatment to ease the acute phase of pain and inflammation. These interventions include

* brief rest until the acute phase of pain has decreased (ie, indefinite bed rest is no longer recommended for patients with back pain);

* moist heat to the affected area;

* muscle relaxant medications to treat pain-related muscle spasms;

* nonsteroidal anti-inflammatory drugs (NSAIDs) or steroid medications to relieve inflammation and pain;

* opioid analgesia for immediate relief, although older adults may experience undesirable side effects from narcotic administration;

* physical therapy and exercise to ease pain, improve mobility and flexion, and strengthen abdominal and back muscles to support the spine; and

* weight loss, if needed, to decrease pain resulting from increased load bearing.1,7,14

Epidural steroid injections (ie, a combination of a steroid medication and/or local anesthetic injected via the epidural space of the spinal cord for pain relief and inflammation) may be given when most conservative measures have failed.7,15 Surgery becomes a reasonable option when patients experience continued significant and debilitating pain that is not relieved or eased after at least six months of conservative treatment.

SPINAL FUSION

Spinal fusion currently is the treatment of choice for patients with DDD in the United States.1,2,9 In spinal fusion, the diseased disc is removed, and either autologous bone via an iliac bone crest harvest or donor allograft is placed in the space to create a bony fusion between the vertebrae. Often, pedicle screws, rods, or interbody cages are implanted to add stability to the spine. This method isolates and immobilizes the painful motion segment of the spine and also halts the degenerative process at that level. The motion segment is composed of the upper and lower vertebral bodies, disc, and facet joints with connecting ligaments that comprise a small portion of the total movement of the entire spine. Many patients have pain relief after undergoing a spinal fusion; it commonly is theorized that the source of DDD pain is movement of the involved segment and overall axial force instability.2,3,14

Spinal fusion offers numerous benefits; it

* provides pain relief,

* provides spinal stability,

* reestablishes disc height, and

* halts the degenerative process at the diseased level.2,3,14

Annually, some 200,000 people undergo discectomies with or without spinal fusion with an overall success rate of 90%.1,16 Technological and osteobiological advances in implants, such as titanium rods and screws, interbody cages, allograft bone, demineralized bone matrix, bone-morphogenic proteins (BMPs), plateletrich plasma, and osteoconducive bone grafts, have made fusions more successful than ever and have made iliac bone crest harvest an optional rather than a necessary choice.3

Titanium rods, screws, and interbody cages help stabilize the vertebral bodies until fusion has taken place. One advantage of using titanium over stainless steel is that fluoroscopic images are not blurred, allowing for correct placement. The greatest advantage that titanium has over stainless steel, however, is that titanium is compatible with magnetic resonance imaging (MRI) scanning for future patient diagnostic testing.17

Allograft bone is procured from cadaver donors and processed for use by manufacturers. Using allograft bone eliminates the need for taking an iliac bone graft, which causes the patient significant pain and increases the risk of infection; however, the supply of allograft bone may not meet demand.3,17

Demineralized b\one matrix consists of human bone.3,17 An advantage of demineralized bone matrix is that this allograft can be used in putty form to fill bone defects. Other forms of allografts usually come in premade shapes, such as dowels or cubes.

Bone morphogenic protein is a relatively new, genetically engineered protein recently approved by the US Food and Drug Administration (FDA). It can be added to a collagen sponge or other implants (ie, titanium interbody cages) to stimulate bone growth and increase the speed and effectiveness of fusion.3,17,18

Platelet-rich plasma combines the patient's own plasma with demineralized bone matrix and a calcium/thrombin carrier. This combination assists the patient's body in cell growth and healing.

POSTOPERATIVE CONSIDERATIONS AND COMPLICATIONS. It takes approximately three to six months and can take as long as 18 months after bone graft and implants are surgically placed for the involved spinal segments to fuse.2,6,16 Physicians may recommend that the patient wear a brace or corset to support the back and encourage good posture. Physical therapy and exercise programs help the patient regain movement.

Many patients experience relief of symptoms as pressure is taken off of irritated nerve roots. Some patients, however, experience adverse effects, such as vascular or durai tears, chronic pain or stiffness, or failed back syndrome, which may indicate the need for additional surgery at the same or other levels.2-5,7,10

Although, spinal fusion is designed to limit the movement of the painful joint segment, it may lead to increased stress and motion in the adjacent motion segments above and especially below the fused area, often leading to an accelerated degenerative process in those areas.2,5,7,10,14 Studies have demonstrated that fusion can cause an increase in adjacent level motion and an increased load on the facet joints at the adjacent levels up to 96% compared to the nonsurgical segments.4,19

ARTIFICIAL DISC REPLACEMENT

On Oct 26, 2004, the FDA approved an artificial disc for the treatment of DDD at L4 to SI.3,7,9,16 The artificial disc originally was developed in 1987 by two orthopedic surgeons at the Charite Clinic in Berlin and presently is the only disc approved for use in the United States.9 The artificial disc offers an alternative to spinal fusion for treatment of DDD at these levels and is designed to preserve spinal motion and recreate the natural function of the disc.2,3,7,9

Ideally, the benefit of an artificial disc, or a prosthetic nucleus, would be to restore the natural kinetic motion of the spine while maintaining disc height and providing stability without causing adjacent segment disease. In addition, the patient would experience pain relief and return of normal function. The challenge is in developing a long-term device that will not wear out, loosen, or be expelled. Current joint replacements for arthroplasty have a life span of approximately 10 to 15 years.2,3 The average age of a patient undergoing artificial disc replacement is approximately 35 to 40 years, therefore, implant longevity is an important factor to consider.1-3,9

Based on wear debris testing, the wear rate of the recently approved disc is 1.1 mg per 10 mil cycles, which is the equivalent of 80 years of significant bending with 10 kg weights in each hand.9(p9)

Clinical testing of this disc during the past 20 years appears to support this data.3,6,7,20

HISTORY OF DISC REPLACEMENT. Attempts at artificial disc replacement began as early as 40 years ago. In 1966, results of clinical trials were published about 125 patients in whom ball bearings were implanted into their lumbar and cervical disc spaces after they had undergone a discectomy.21 The surgeon theorized that the ball bearings would create a ball-joint mechanism that would restore normal disc function. Although the results initially were promising, 88% of the patients had experienced subsidence (ie, loosening and expulsion of the implants) by a four- to seven-year follow-up.8,21

Artificial disc designs currently are undergoing FDA trials in the United States and clinical trials in Europe and South Africa. One design is a hydraulic artificial disc with a hydrocel core that absorbs fluid to expand and restore disc space height. Another design is an elastic disc with a rubber or silicone core banded to two titanium endplates. Some discs have constrained and unconstrained mechanical designs, such as metal endplates with ball bearings, metal hinges with springs, and discs with polyethylene endplates. Most of these designs, with the exception of the rubberized, elastic disc, have met with positive results.2,3

The US-approved disc has an unconstrained design comprised of two metal endplates made of chromium and cobalt with teeth that anchor into the upper and lower vertebra of the affected joint segment. A free-floating polyethylene core with a radiographic strip is placed between the endplates.3,7,22 Correct surgical placement and sizing of the implant, as well as the body's axial load in the lower vertebra, keep the implant in place.322 The components of the artificial disc are composed of materials used in other joint arthroplasty implants that have proven to be well tolerated by the human body.7,9

Newer versions being used in Europe have an osteoconducive coating on the metal endplates to stimulate bone growth.3 The sliding-core design allows for biomechanical movement of the lumbar spine that duplicates normal movement (eg, flexion, extension). After extensive testing, its components have proved to be sturdy with little wear and tear.7,9,22 In 1997, one researcher reported that 84.8% of 105 patients in whom this disc was implanted had good or excellent clinical outcomes after five years, and in 2002, it was reported that there were good or excellent clinical outcomes in 90 of 100 patients at a 10-year follow-up. There were no device failures in either study.3 Similar results have been achieved worldwide.3,23,24

Since 1987, the disc has undergone three design changes and has become the most widely used and most clinically tested treatment for DDD. More than 7,000 procedures have been performed worldwide, and success rates are similar to those for spinal fusion.2,3,6,7,9

FDA CLINICAL TRIALS. In the United States, PDA investigational device exemption (IDE) clinical trials for this artificial disc involved 14 centers across the country. Patients (N = 304) were randomly assigned to receive either the artificial disc (n = 204) or a titanium interbody cage with iliac bone crest graft via the anterior lumbar intradiscal fusion approach (n = 99).3 The results were similar with regard to patient pain and neurological complications based on Oswetry Disability Indicator (ODI) scores. Physicians use the ODI scale to determine the severity of complications that patients with spine disease experience.

The inclusion criteria for participation in the study were strict. Only patients between the ages of 18 and 60 with one level DDD at L4-5 or L5-S1 confirmed by medical history, MRI, x-ray, and discography whose condition had not improved after at least six months of conservative treatment were included. Patients with radicular pain were excluded unless leg pain was caused by referred pain. Patients underwent a clinical follow-up assessment at intervals of three, six, 12, and 24 months postoperatively with radiographie testing at each visit. The two-year study demonstrated that the clinical outcomes of the study group were equivalent or better in terms of ODI scores to those of patients who received the titanium interbody cage in a spinal fusion procedure.3

Patients involved in FDA IDE trials who underwent artificial disc replacement experienced shorter recovery periods with decreased hospital stays and faster pain relief than patients who underwent spinal fusion. As a result, patient satisfaction was higher in the artificial disc replacement group.2,3,7

CANDIDATES FOR ARTIFICIAL DISC REPLACEMENT. The criteria for artificial disc candidates are similar to those for patients selected for the FDA IDE trials. Patients must

* be between the ages of 18 and 60;

* have one diseased disc level at L4-5 or L5-S1;

* have DDD confirmed by medical history, MRI, x-ray, and discogram; and

* have undergone six months of conservative treatment without experiencing relief of their discogenic back pain.2,3,7,9

The metal endplates of the implant must be able to grab onto solid bone for the prosthesis to be effective, and the surgical approach is via the abdominal retroperitoneal route. Contraindications to surgery, therefore, are

* allergies to metal,

* autoimmune disorders,

* discal instability at more than one spine level,

* facet joint disease,

* history of chronic steroid use,

* infection,

* morbid obesity,

* osteoporosis or osteopenia,

* pregnancy,

* previous back surgery with the exception of discectomy or laminectomy at the same level,

* spondylolisthesis greater than 3 mm,

* scoliosis, or

* spinal tumor.2,3,7,9

SURGICAL PLACEMENT OF AN ARHFICIAL Disc

The surgeon performs a history and physical examination to define the patient's pain, after which the patient may undergo a discogram (ie, contrast dye is injected under fluoroscopy) to help determine if the disc is generating the patient's pain. The patient then undergoes a preoperative x-ray or MRI scan to ensure that he or she meets the inclusion criteria and can gain the most benefit from artificial disc replacement. The x-ray and MRI also give the surgeon an estimate of implant size.3,9,22

Perioperative personnel place the patient in a supine position on an OR bed that has fluoroscopy capacity. The bed must have the ability to break in the center (eg, a kidney rest) to open the spine for lordotic angulation during prosthetic placement. The circulating nurse and anesthesia care provider ensure that the patient's arms are positioned to allow the mobile fluoroscopy unit to be moved intoposition for the procedure. Due to the invasive nature of the surgical procedure, most patients undergo general anesthesia. Regional anesthesia (ie, spinal, epidural) is not recommended because neurovascular checks must be performed immediately after surgery because of the close proximity of the spinal cord during surgical intervention.9,12

A radiology technologist carefully defines and marks the midline of the vertebral body. This is accomplished by performing accurate fluoroscopy via the Ferguson anterior-posterior (AP) approach before the procedure is started for device placement during surgery.

A 4-cm to 6-cm skin incision is made below the umbilicus using a left retroperitoneal approach.22 The circulating nurse preps the patient from below the nipple line to the groin with a solution chosen by the surgeon who will perform the access portion of the procedure. Draping is dependent on individual surgeon preference and facility policy.

Artificial disc replacement surgery can be challenging to perform for surgeons who are not experienced in performing spinal surgery via the anterior approach. A vascular or general surgeon trained in spinal access usually provides spinal access and isolates the iliac vein and artery. After spinal access and visualization have been established, the orthopedic or neurosurgeon performs a complete discectomy at the designated level and uses special, long instruments to test the intervertebral space for proper size, placement, and lordotic angulation of the implant. There are five different sizes of endplates and cores designed to fit individual patient sizes. The surgeon prepares the vertebral bodies for the endplates and uses a special inserting instrument to place the endplates in the space as the space is distracted. He or she uses an impactor to manually engage the teeth located on the endplates into the upper and lower vertebrae of the spine segment.15 The surgeon tests the polyethylene sliding core and then places it between the two endplates. The axial force of the body keeps the device in place (Figure 2).12,13 The radiology technologist performs fluoroscopy so that the surgeon can verify the correct position of the artificial disc in the AP and lateral planes.

Figure 2 The surgeon uses an impactor to manually engage the teeth located on the endplates into the upper and lower vertebrae of the spine segment. The axial force of the body keeps the device in place.

Postoperatively, the anesthesia care provider and circulating nurse transfer the patient to the postanesthesia care unit (PACU) where the patient is monitored for respiratory status, vital signs, level of consciousness, cardiac rate and rhythm, pain, neurovascular status (eg, pulses and sensation of extremities), and incisional status (eg, wound approximation, drainage, dressing). Many surgeons order a patientcontrolled analgesia pump for pain control in the PACU, which may be continued on the medical-surgical unit as needed. The PACU nurse calls report to the nurse who will be assuming patient care on the medical-surgical unit when the patient has met the PACU discharge criteria (eg, stable airway and vital signs, adequate pain control). The report includes the patient's history, surgery performed, and recovery outcomes.

POSSIBLE POSTOPERATIVE COMPLICATIONS. Complications that may occur postoperatively are those that involve both abdominal and spine surgery. They include, but are not limited to,

* anesthetic side effects (eg, dysrythmias, hypotension, hypothermia, hypertension, hypovolemia, postoperative nausea and vomiting);

* bladder problems (eg, difficulty urinating, inability to urinate);

* bleeding and possible need for transfusion;

* device failure and need for additional surgery;

* dural tears;

* ileus;

* incision problems (ie, infection, dehiscence);

* infection;

* pain;

* paralysis;

* spinal fluid leakage; or

* death.7

POSTOPERATIVE ACTIVITY AFTER ARTIFICIAL DISC REPLACEMENT. The patient is discharged from the hospital on approximately the fourth postoperative day if there are no complications. The discharge nurse provides the patient and patient's family members with a written copy of the surgeon's discharge instructions. These instructions encourage the patient with a disc prosthesis to regain mobility and strength by exercise and physiotherapy. The nurse describes initial physical limitations, such as

* no rotation of the lumbar region for three weeks postoperatively;

* no curving of the lumbar region or intense stomach exercise for six weeks postoperatively;

* no participation in sports for three months;

* no activities that stretch the sciatic nerve, if painful; and

* the need to ensure correct posture to avoid putting pressure on the prosthesis.6

FUTURE OUTLOOK

The success of an artificial disc replacement procedure depends on proper patient selection, diagnosis, and specialized surgeon experience with device placement. Current FDA data demonstrate that patients who have undergone spinal arthroplasty with this artificial disc experience results that are comparable to those of patients who have undergone spinal fusion.1 Low incidence of neurological complications during recent PDA trials and almost 20 years of clinical use in Europe point to artificial disc replacement as a safe and effective treatment for mechanical back pain caused by DDD.3 As a result of strict PDA guidelines for patient inclusion criteria, however, only a select population of patients will be eligible for total disc replacement.3 It is predicted that within two years, approximately 20% of all patients with lower level DDD will have undergone artificial disc replacement.7

This evolutionary technology has the potential to positively affect spinal surgery outcomes in the future. Improved versions and additional clinical trials will allow for more clinical applications. Presently, the FDA is evaluating clinical trials involving cervical disc replacement as a further clinical application.23,25-27 Some facilities in the United States already have implanted two artificial discs in the same patient with good results.20 Many surgeons believe that the artificial disc still is controversial, the studies are inconclusive, and that because patient results are the same as the current gold standard of treatment for DDD, spinal fusion is safer and more reliable.16 Only time will tell whether US patients who have undergone artificial disc implantation will have similar clinical outcomes to patients in other parts of the world who have undergone the same procedure.

Examination

Artificial disc replacement-Evolutionary treatment for degenerative disc disease

1. The intervertebral disc (IVD)

1. gives the intervertebral space height and stability.

2. has high water content and a glycoprotein component.

3. loses water content because of disc compression throughout the day.

4. is a cushiony, gel-like shock absorber located between each vertebral body.

5. is a ring of collagen fiber.

a. 1 and 3

b. 2, 4, and 5

c. 1, 2, 3, and 4

d. 1, 2, 3, 4, and 5

2. Nerve impingement can cause

1. bowel or bladder problems.

2. numbness and muscle weakness of extremities.

3. permanent nerve damage if left untreated.

4. sciatica.

a. 1 and 3

b. 2 and 4

c. 1, 2, and 3

d. 1, 2, 3, and 4

3. Indefinite bed rest is the first line of conservative treatment for patients with back pain.

a. true

b. false

4. Traditionally, the treatment of choice for patients who experience continued significant and debilitating pain that is not relieved or eased after at least six months of conservative treatment has been

a. discectomy.

b. epidural steroid injections.

c. laminectomy.

d. spinal fusion.

5. Which of the following are considerations or complications of spinal fusion? It

1. can take three to 18 months for fusion to occur.

2. may cause increased stress and motion in adjacent motion segments.

3. may necessitate use of a brace or corset to support the back.

4. may result in the need for further surgery at the same or other levels.

5. may result in vascular or durai tears, chronic pain or stiffness, or failed back syndrome.

a. 1 and 3

b. 2, 4, and 5

c. 2, 3, 4, and 5

d. 1, 2, 3, 4, and 5

6. The artificial disc replacement procedure described in this article is performed from a/an ______________ approach.

a. anterior

b. Lateral

c. posterior

7. After completing the discectomy, the surgeon tests the intervertbral space for proper size, placement, and __________________ angulation.

a. kyphotic

b. lord otic

c. scoliotic

8. The polyethylene sliding core is kept in place by

a. the teeth located on the endplates of the implant.

b. the axial force of the body,

c. an impactor used to manually engage the vertebral bodies.

9. Some patients may experience difficulty urinating as a postoperative complication of artificial disc replacement surgery.

a. true

b. false

10. Initial physical limitations to which patients undergoing artificial disc replacement must adhere include

1. no curving of the lumbar region or intense stomach exercises for six weeks.

2. no lumbar rotation for three weeks.

3. no participation in sports for three months.

4. no lifting of objects greater than 10 pounds for six months.

5. no activities that stretch the sciatic nerve.

6. ensuring correct posture to avoid putting pressure on the prosthesis.

a. 1, 3, and 5

b. 2, 4, and 6

c. 1, 2, 3, 5, and 6

d. 1, 2, 3, 4, 5, and 6

Spinal fusion surgery entails removing the diseased disc and placing either autologous bone via an iliac bone crest harvest or donor allograft in the space to create a bony fusion between the vertebrae.

Spinal fusion limits movement of the painful joint segment, causing increased stress and movement in adjacent motion segments, which can lead to accelerated degeneration in those areas.

The sliding-core design allows for biomechanical movement of the lumbar spine that duplicates normal movement (eg, flexion, extension).

The patient undergoes a discogram to determine if the discis causing his or her pain and an x-ray or magnetic resonance imaging scan to ensure that he or she meets the inclusion criteria.

Low incidence of neurological complications and almost 20 years of clinical use in Europe indicate that artificial disc replacement is a safe and effective treatment for degenerative disc disease.

NOTES

1. V Tranellis, R Haid, "Spinal disc replacement: The development of artificial discs," Spineuniverse.com, http://www.spineuniverse .com/disrjlayarticle.php/article501.html (accessed 6 June 2005).

2. V Traynellis, R Haid, "Artificial disc, the future is bright," Spineuniverse.com, http://ivwio.spineuniverse.com/displayarticle .php/articlcl 520.html (accessed 27 June 2005).

3. F H Geisler et al, "Neurological complications of lumbar artificial disc replacement and comparison of clinical results with those related to lumbar arthrodesis in the literature: Results of a multicenter, prospective, randomized investigational device exemption study of Charite intervertebral disc," Journal of Neurosurgery Spine I (September 2004) 143-154.

4. B W Cunningham et al, "Biomechanical evaluation of total disc replacement arthroplasty: An in vitro human cadaveric model," Spine 28 (October 2003) S110-S117.

5. A S Hilibrand et al, "Radiculopathy and myelopathy at segments adjacent to the site of a previous anterior cervical arthrodesis," Journal of Bone and Joint Surgery (Am) 81 (April 1999) 519-528.

6. "Artificial disc replacement," Fabian-Bitan.com, http:// www.bitanmd.com/disc.html (accessed 28 June 2005).

7. "Charite artificial disc," DePuy Spine, http:// www.charitedisc.com/charitedev/domes tic/default.asp (accessed 27 June 2005).

8. B H Cummins, J T Robertson, S S Gill, "Surgical experience with an implanted artificial cervical joint," Journal of Neurosurgery 88 (June 1998) 943-948.

9. Surgical Technique for the Charite'rM Artificial Disc with Centreline TDR Instrumentation (Raynham, Mass: Depuy Spine, 2004).

10. G Ghiselli et al, "Adjacent segment degeneration in the lumbar spine," Journal of Bone and Joint Surgery (Am) 86-A (July 2004) 1497-1503.

11. E Gross, "Acute lower back problems in adults-Facet joint injection," Spineuniverse.com, http://www.spineuniverse.com / displayarticle.php/artidel420.html (accessed 27 June 2005).

12. E T Murphy, "Neurosurgery," Alexander's Care of the Patient in Surgery, 12th ed, J C Rothrock, ed (St Louis: Mosby, 2003) 931- 999.

13. R Berkow et al, Merck Manual of Medical Information (Whitehouse Station, NJ: Merck Publishing Co, 1997) 322-330.

14. K Foley, "Artificial disc replacement and degenerative disc disease," Spineuniverse.com, http://www.spineuniverse .com/display article.php/articlel681.html (accessed 27 June 2005).

15. G G Bart, "Epidural injection for low back and leg pain," Spineuniverse.com, http://www.spineimiverse.com/displayarticle .php/ artide604.html (accessed 27 June 2005).

16. S Agazzi, A Reverdin, D May, "Posterior lumbar interbody fusion with cages, an independent review of 71 cases," Journal of Neurosurgery 91 suppl 2 (October 1999) 186-192.

17. G Rodts, "Advancements in spine surgery," Spineuniverse.com, http://www.spme universe.com/displayartide.php/article513.html (accessed 27 June 2005).

18. J C Wang, "BMP: Fusion made better," Spineuniverse.com, http:/ /ivww.spineuni Oerse.com/displayarticle.plip/articlel 711.html (accessed 27 June 2005).

19. M Moumene, F H Geisler, "Effect of fusion vs total disc replacement on the facet loading of adjacent segment: A finite element analysis," Journal of Neurosurgical Spine 1 (September 2004) 146.

20. "First two level artificial disc surgery in US performed at Saint Joseph Medical Center," St Joseph Medical Center, http:// www.sjmcmd.org/news/First-Two-Level-Arti ficial-Disc-Surgery-in-US- Performed-at-SJMC .cfm (accessed 6 June 2005).

21. L Sekhon, "Spine specialists on-call: Artificial disc surgery- Fad or real breakthrough?" Spineuniverse.com, http://www .spineunwerse.com/displayarticle.php/article 2135.html (6 June 2005).

22. The Charite(TM) Artificial Disc (Raynham, Mass: Depuy Spine, 2004).

23. G Cinotti, T David, F Postacchini, "Results of disc prosthesis after a minimum follow up of 2 years," Spine 21 (April 15, 1996) 995-1000.

24. W S Zeegers et al, "Artificial disc replacement with the modular type SB Charite III: 2-year results in 50 prospectively studied patients," European Spine Journal 8 (1999) 210-217.

25. Stryker Announces Acquisition of SpineCore, Inc (news release, Summit NJ: Stryker, July 21, 2004). Also available at http:/ /www.vertical-group.com/PDFs/pr-news 072104.pdj#search=Flexicore%20by%20 Stryker' (accessed 6 June 2005).

26. Synthes-Stratec Announces FDA Notification That it May Begin the ProDisc Cervical-C IDE Disc Replacement Clinical Trial (news release, Oberdorf, Switzerland: Synthes-Stratec, July 30, 2003). Also available at http://ivivw.synthes.com/litml/Jul_30 _2003.4514.0.html (accessed 6 June 2005).

27. R C Sasso, "Prestige disc for cervical artificial disc replacement," Spineuniverse.com, http://www.spineuniverse.com/ displaiiartkle.php/ articleW78.html (accessed 27 June 2005).

Susan Bajnoczy, RN

Susan L. Bajnoczy, RN, is a clinical nurse IV neurosurgery coordinator for surgical services at VCU medical Center, Virginia Commonwealth University, Richmond, Va.

Editor's note: The author acknowledges Brace Mathern, MD, neurosurgeon; Deborah Boiling, RN, nursing director of surgical services; Chris Graham, RN, MSN, nursing manager of surgical services; and Troy Hooks, care partner at VCU Medical Center, and Paul Bajnoczy for their support in writing this article.

Copyright Association of Operating Room Nurses, Inc. Aug 2005

Source: Association of Operating Room Nurses. AORN Journal

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