What is a Cervical Disc Arthroplasty?

A cervical disc arthroplasty (CDA, a.k.a. cervical artificial disc or disc replacement) is a surgical procedure used to treated degenerative disc disease (DDD) in the cervical spine. In contrast to the more commonly performed anterior cervical discectomy and fusion (ACDF), a CDA preserves motion between two vertebral bodies after the disc is removed.  This preservation of motion is thought to prevent adjacent segment degeneration (ASD, see What is Adjacent Segment Degeneration?) seen after some spinal fusion procedures.  

In discussing CDA it helps to consider the concept of a spinal motion segment. A motion segment is a group of components of the spine that act together to allow movement at that level of the spine (see figure 1).  These are the bones of the spine as well as the intervertebral disc (IVD) and facet joints in between them. For example the C5/6 motion segment is comprised of the bones of C5 and C6 as well as the C5/6 disc and facet joints. These components allow for a few degrees of movement (more or less depending on the level of the spine) and thereby contribute to the overall movement of the spine.  

Spinal Motion Segment

FIgure 1: A spinal motion segment in flexion and extension. The facet joints are indicated by the black arrows. (Source: http://www.spineinfo.co.uk/anatomy-of-the-spine/)

Recall that in an ACDF (see What is an ACDF? Part I and Part II) a degenerated or herniated IVD is removed and a spacer is inserted in its place.  Over time the body will grow bone across the spacer thereby joining, or fusing, the two vertebral bodies together to immobilize the diseased motion segment.  This alters the local biomechanics of the spine and may place more strain on the motion segment above or below thereby causing more rapid degeneration of that segment, i.e. ASD.  The initial steps of a CDA are identical to those of an ACDF: the spine is exposed via an incision on the front of the neck and a discectomy (removal of the disc) is performed to decompress a pinched nerve or the spinal cord (see radiculopathy and myelopathy.)  The key difference between CDA and ACDF is the type of device inserted into the disc space after the discectomy.  Rather than a spacer and bone graft (and sometimes a plate), the surgeon inserts a special device that bends and rotates around an axis of rotation (see figure 2 and video). This device allows for movement at the motion segment that mimics the natural motion afforded by a healthy IVD (hence the term “artificial disc.”) The hope is that if we preserve the motion of the segment we avoid altering the biomechanics of the spine and thus decrease the incidence of ASD.  It’s a great idea in theory but what does the literature say about CDA? 

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Figure 2: Various types of CDA devices. (Source: Alvin et al, 2014)

Video: One type of CDA device (Nuvasive PCM) in motion.

First, the data clearly demonstrates that CDA is at least as safe and effective as ACDF (arguably the most successful surgical procedure we do in neurosurgery.)  The data is less clear about differences in rates of ASD in patients who undergo CDA versus ACDF.  This is mainly because a) the rates of ASD are generally low for either ACDF or CDA (around 3% per year), and b) it can take years for ASD to develop.  If you combine these factors you need thousands of patients and many years of data collection to begin to detect a difference in rates of ASD between patients who undergo CDA versus ACDF.  Thus the data can be murky.  One large Cochrane review of 9 studies with 2400 patients showed no difference is ASD rates at 2-years (Boselie et al, 2013).  A review of the 7-year data on the Medtronic Prestige CDA device, however, showed a 7-year rate of ASD of 4.6% in CDA patients versus 11.9% for ACDF patients (Burkus et al, 2014). One must view this data with caution, though, because of potential conflict of interest:  the study was written and edited by scientists paid by the Medtronic Corporation and the lead author Dr. Kenneth Burkus is listed as a paid consultant for Medtronic.  Indeed a large review of 74 randomized controlled trials of CDA versus ACDF found significant conflict of interest in the majority of trials on the subject.  When the authors eliminated trials with conflict of interest they found no difference in rates of ASD in CDA versus ACDF (Alvin et al, 2014).  Despite not showing a statistically significant difference in rates of ASD for CDA versus ACDF, most studies show a trend towards improved rates of ASD for CDA.  Most authors believe that a few more years of data should settle the debate. For what it’s worth, I personally believe that CDA does prevent ASD when compared to ACDF. 

CDA isn’t for every patient.  The ideal patient for CDA in my mind is a young patient with an otherwise healthy spine who has radiculopathy or myelopathy from an acute disc herniation (i.e. one of the young Marines I see from Camp Lejeune).  I would NOT use CDA in an older patient with multiple severely degenerated discs or severe cervical spondylosis.  While my indications for CDA are typically narrow, more and more surgeons are expanding their indications for CDA (including treating multiple degenerated discs) with excellent outcomes.  

Thanks for reading.  Merry Christmas and Happy New Year!

J. Alex Thomas, M.D.

Sources:

Alvin, M. D., Abbott, E. E., Lubelski, D., Kuhns, B., Nowacki, A. S., Steinmetz, M. P., … Mroz, T. E. (2014). Cervical arthroplasty: a critical review of the literature. The Spine Journal : Official Journal of the North American Spine Society, 14(9), 2231–45. 

Boselie, T. F. M., Willems, P. C., van Mameren, H., de Bie, R. a, Benzel, E. C., & van Santbrink, H. (2013). Arthroplasty versus fusion in single-level cervical degenerative disc disease: a Cochrane review. Spine, 38(17), E1096–107. 

Burkus, J. K., Traynelis, V. C., Haid Jr., R. W., & Mummaneni, P. V. (2014). Clinical and radiographic analysis of an artificial cervical disc: 7-year follow-up from the Prestige prospective randomized controlled clinical trial. Journal of Neurosurgery: Spine, 21(October), 516–528.

 

What is Laser Spine Surgery?

One of the most common questions that I get asked in my clinic (more so than any question about stem cells) is “are you going to use lasers in my surgery?” This usually comes up after I describe a minimally-invasive technique used to perform a particular operation.  To the average patient the term “minimally-invasive” sounds advanced and I think it’s a natural leap to consider laser spine surgery (LSS) in the same breath.  Also, while I was once aggravated by these questions, I realize now that one can’t blame patients for being interested in LSS. The centers that perform these procedures spend millions of dollars each year bombarding prospective patients with print, TV and especially Google targeted advertising.  These advertisements portray LSS as a high-tech alternative to conventional spinal surgery (because hey, if lasers are involved then it must be high-tech and therefore better for one’s health than non-laser spine surgery, right??) 

I’m not going to use this post as a forum to share my personal feelings about LSS (I don’t want to get a cease and desist letter from lawyers representing LSS centers.)  I’m also not going to get into the growing number of high-profile lawsuits against LSS centers for malpractice and unethical practices. Rather, I’ll just outline a few facts about LSS and will let you, learned Spinal (con)Fusion readers, be the judge. Many of these facts are outlined in more detail in an excellent Bloomberg News exposé about LSS that I encourage you to read (I am considering handing out print copies of this exposé in my waiting room.)

Fact #1: The limited use of lasers in the treatment of herniated discs in the lumbar spine was first described nearly 30 years ago. These ablation procedures employ a laser deployed via a fine cannula into the disc near a contained disc herniation (sometimes called a “bulge”) that is compressing a nerve root.  Once there the laser heats (or ablates) the nucleus pulposus (NP) near the disc herniation thereby causing the water molecules within the NP tissue to evaporate. This creates a void within the disc which theoretically creates negative pressure that “sucks” the herniated fragment back into the disc space and off of the nerve root.  In other reported techniques a laser is used to directly degrade a herniated disc fragment as an adjunct to a traditional lumbar microdiscectomy procedure.  While variations of these techniques have been performed for decades now, their efficacy as treatments for herniated discs has never been validated with sound randomized controlled data.  Yes, a search of the pubmed database for “laser spine surgery” does reveal several studies. Most of these studies, though, are heavily biased observational studies with small numbers of patients, published in obscure journals such as Photomedicine and Laser Surgery and not in any of the core clinical journals of spinal surgery.  It’s also important to note that even in these lesser quality studies most of these ablation techniques are only advocated for a very small subset of patients with “contained” disc herniations, not those with free disc fragments or in patients with annular tears (thereby ruling out the majority of patients with lumbar degenerative disc disease)  Thus, if the use of lasers in spinal surgery has only been described for a very small subset of patients (with only limited success at that), how can it be advocated by LSS centers for the treatment of the many other degenerative spinal conditions that they purport to cure?  Personally, I’ve only used lasers during spine surgery to remove complex spinal tumors.  I don’t believe LSS is an effective treatment for herniated discs (or any other degenerative condition of the spine) and therefore would never offer LSS to a patient over standard minimally-invasive surgical treatments.  

Fact #2: Your insurance company probably isn’t going to pay for LSS.  I’ve seen many patients in my office who have travelled to an LSS center for a consultation.  They tell me about cash fees of $15,000-$30,000 that must be paid prior to treatment.  Why? Because (I can’t believe I’m putting this in writing) the people who work at insurance companies aren’t stupid and know that there isn’t good data supporting LSS.  If there isn’t good data they’re not going to pay for the procedure and the patient gets stuck with the bill for that high-tech laser.  Ordinarily the governing societies of spinal surgery argue quite vehemently in favor of surgeons versus insurance companies when it comes to surgical procedures being denied coverage.  The fear is that once one procedure is denied coverage the insurance companies will feel emboldened to look for reasons to not cover others.  Recently, however, in an unprecedented move the North American Spine Society, arguably the world’s most prominent society of spinal surgeons, recommended that insurance providers not cover LSS procedures. Citing a “lack of quality clinical trials concerning laser spine surgery in the cervical and lumbar spine” the authors of the coverage recommendations state that “laser spine surgery…is NOT indicated at this time.”  Thus, if you’re considering LSS be prepared to pay out of pocket for it.  The irony is that lasers aside, in the end you’re going to pay thousands of dollars in cash for the same minimally-invasive procedure that I and any other reputable minimally-invasive surgeon would provide under your insurance coverage. Oh, and most incisions from standard minimally-invasive procedures can also be covered by a Band-Aid. 

Fact #3: Your doctor isn’t going to refer you for LSS.  Traditionally, a primary care physician (PCP) refers his patients to specialists who have provided good, safe care to his patients in the past.  He does this because he, more than any other physician, has his patients’ best interests at heart.  This vetting process is an important safeguard against specialists practicing subpar medicine.  Chances are, specialists who perform unnecessary surgeries or consistently have poor outcomes won’t be referred patients and therefore will be run out of town.  LSS centers rely on a different model in which medical services are offered directly to the consumer.  These services are offered via relentless advertising on TV, online and in “seminars” all over the country.  This then allows patients to find their way to an LSS center without the guidance of their PCP.  Why is this bad? Because unlike on that ad on TV for the latest cholesterol drug, the claims about outcomes and risks made by LSS centers isn’t screened as closely by the Food and Drug Administration.  Thus, patients suffering from degenerative conditions of the spine, patients that are often in severe pain and desperate for relief, are vulnerable to exploitation.  

I’ve found that if a patient has his mind set on pursuing LSS they will do so regardless of what I just discussed.  Ultimately, though, I will always encourage him to a) look at the data about LSS, b) be skeptical of any medical service or procedure that requires a substantial cash payment up front, and c) trust that their PCP will have their best interests at heart and will refer him to the best specialist for his care.

Thanks for reading.

J. Alex Thomas, M.D.

Sources:

1. Singh V, Manchikanti L, Calodney AK, Staats PS, Falco FJE, Caraway DL, et al.: Percutaneous Lumbar Laser Disc Decompression: An Update of Current Evidence. 229–260, 2013

2. Back-Surgery Center Dangled Illegal Incentives, Lawsuit Alleges: http://www.businessweek.com/articles/2014-10-15/laser-spine-institute-dangled-illegal-incentives-to-attract-back-surgery-patients-lawsuit-alleges

3. Bloomberg exposé: http://www.bloomberg.com/news/2011-05-04/laser-spine-surgery-more-profitable-than-google-sees-surge-in-complaints.html

4. NASS coverage recommendations: https://www.spine.org/Documents/PolicyPractice/CoverageRecommendations/LaserSpineSurgery.pdf

 

The Biologics of Degenerative Disc Disease, Part II: Stem Cell Therapies

Perhaps nothing captures the imagination of scientists and the general public alike more than the potential of stem cell therapies.  These therapies direct pluripotent cells (i.e. cells that can become any cell in the body) to replenish cells that have been damaged or depleted by disease processes.  Think diabetes, Parkinson’s Disease, ALS and even spinal cord injury.  While the reality of stem cell therapies hasn’t always lived up to our expectations, the field of stem cell therapy research is still in its infancy and I think we have only begun to see the power of these therapies.  One of the areas where stem cell therapies are starting to gain traction is in the treatment of DDD.  

In our last post we discussed how a concoction of growth factors and cytokines maintains the health of the structural components of the intervertebral discs (IVDs).  (For simplicity’s sake we’ll refer to these structural components wholly as extracellular matrix, or ECM.)  These growth factors and cytokines stimulate cells within the IVD to produce ECM.  For reasons that are not yet fully understood the populations of these cells, and thus amounts of ECM they produce, are depleted over time.  This is where we get a “Chicken or Egg” scenario: is degenerative disc disease (DDD) caused by the loss of these cells or is some other trigger of DDD (i.e. years of mechanical stress) the cause of the loss of these cells.  I’m not sure that the answer to this question is know yet, but what is known is that these populations of cells are tremendously important to the health of the IVD. The goal of stem cell therapies for DDD is to replace or regenerate these populations of IVD cells with the goal of replenishing the ECM components that give the disc its form and function.  Sounds simple, right? 

It turns out that it’s actually quite complicated.   The first obstacle to overcome is where to get the “starter” cells used to replenish the lost populations of IVD cells.  Probably the most straightforward way to replenish these cells is to just find a source of mature IVD cells for harvest.  Some studies have looked at harvesting cells from herniated pieces of disc material removed at surgery.  The number of cells within the IVD is quite low (they make up only 1% of the total disc volume) so after the cells are harvested from the disc fragments they must be cultured and multiplied until millions of cells are present. The cells can then be transplanted back into the diseased disc.  Animal studies have confirmed that this is a viable method of increasing the number of IVD cells present and that these cells can improve the health of the IVD (See Figure 1).  In one human study, the EuroDisc trial, cells were cultured and multiplied to over 5 million cells and then transplanted back into diseased discs at 12-weeks (so another procedure was required.)  Although no placebo was used and there certainly were flaws in the assessment of outcomes, an initial analysis of EuroDisc data in 2008 revealed a decrease in pain and increase in disc hydration (as measured with MRI) at 2-year follow-up in patients who underwent cell transplantation versus controls.  A more thorough analysis of their data was due out a few years ago but to my knowledge hasn’t been released.  

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Figure 1. Specimens from dogs treated during animal phase of EuroDisc investigations.  These are gross specimens analyzed 6-months after treatment.  Image A is a control injured disc, note the dusky color, height loss and loss of distinction of the central nucleus pulposus. Image B is an injured disc injected with hyaluronic acid, looks even worse. Image C is an injured disc injected with adipose-derived stem cells while image D is a normal, uninjured disc.  Note how the color, height and nucleus pulposus are preserved. (Source: Hohaus C, Ganey TM, Minkus Y, Meisel HJ: Cell transplantation in lumbar spine disc degeneration disease. Eur Spine J 17 Suppl 4:492–503, 2008. Figure 6.)

Another way to grow a population of IVD cells is to start with true, pluripotent stem cells.  These cells, capable of growing into a variety of tissue types, can be directed to become mature IVD cells. One main benefit of using stem cells as starter cells is that they can be easily obtained from the patient without the need for a spinal procedure to remove a piece of herniated disc to harvest cells from.  The stem cells we’re discussing here aren’t embryonal stem cells which are harvested from an aborted fetus and thus are morally objectionable to some.  Rather, these stem cells are mesenchymal stem cells (MSCs).  The standard site of harvest of these MSCs is the bone marrow although other sites such as adipose tissue are becoming popular as well (so as a bonus you can get a liposuction during cell harvest!).  Once MSCs are harvested they are cultured under specific conditions to become cells similar to those native to the IVD.  These cells are then reimplanted into diseased discs to, it is hoped, regenerate the structural integrity of the disc.  The feasibility of these methods has been confirmed in several animal studies.  One pilot study done in humans (Orozco et al, 2011) has demonstrated not only feasibility and safety but also favorable clinical results in 10 patients with chronic back pain implanted with harvested MSCs.  

In our third and final post of this series we’ll discuss some of the difficulties with MSC transplantation as well as some novel strategies that help overcome these difficulties. 

Thanks for reading!

J. Alex Thomas, M.D.

Sources:

1. Chan SCW, Gantenbein-Ritter B: Intervertebral disc regeneration or repair with biomaterials and stem cell therapy–feasible or fiction? Swiss Med Wkly 142:w13598, 2012 Available: http://www.ncbi.nlm.nih.gov/pubmed/22653467. Accessed 17 July 2014

2. Hohaus C, Ganey TM, Minkus Y, Meisel HJ: Cell transplantation in lumbar spine disc degeneration disease. Eur Spine J 17 Suppl 4:492–503, 2008.

3. Orozco L, Soler R, Morera C, Alberca M, Sánchez A, García-Sancho J: Intervertebral disc repair by autologous mesenchymal bone marrow cells: a pilot study. Transplantation 92:822–8, 2011.

4. Sivakamasundari V, Lufkin T: Stemming the Degeneration: IVD Stem Cells and Stem Cell Regenerative Therapy for Degenerative Disc Disease. Adv Stem Cells:2013.

The Biologics of Degenerative Disc Disease, Part I

I apologize for the long time in between posts.  I was away dealing with a little something called my oral boards.  The board certification process in neurosurgery typically takes several years as the surgeon has to accrue case data for review by members of the American Board of Neurological Surgeons (ABNS).  This long and tedious process begins with a written exam at the end of residency and culminates with a 3-hour oral exam several years into practice.  During this oral exam you are presented case after case to see how you manage typical situations in the O.R., including complications.  I just received word that I passed and am now officially a “board-certified” neurosurgeon.  Believe me, I am thrilled that this hurdle is behind me.

I thought I’d take a break from our march through the various topics of cervical pathology and talk about something that I came across in the mass media not too long ago.  Patients frequently ask me “well Doc, isn’t there something you can inject into my disc to make me all better?”  The short answer is no, not yet, but there may be soon.    In the next two posts we’ll discuss the basic science behind restorative therapies for degenerative conditions of the spine.  In the first part we’ll discuss a recently developed injection therapy that has been shown to block inflammatory mediators that may be important in degenerative disc disease (DDD.)  In the next post we’ll discuss stem cell therapies for DDD.   I’ll refer to these topics collectively as the biologics of DDD.   

NewImage

On the cover of March 2014 issue of Men’s Journal there is a header that reads “NO SURGERY REQUIRED-High Tech Treatments for Knees & Backs.”  (Note: I will NOT use this as an opportunity to vent about how sick and tired I am of the mass media’s assault on the efficacy of spinal surgery and the integrity of spinal surgeons.)  The article describes a process in which a patient’s blood is incubated and injected (as autologous conditioned serum or ACS) into an inflamed joint or spine.  This process, patented by a German orthopedic surgeon, Dr. Peter Wehling, as Regenokine, is heralded as a “painless” way for patients suffering from the chronic pain of chronic arthritis to avoid surgery (which as described so eloquently in the article “sucks in general.”)  Now, I am always initially suspicious of a treatment that a) hasn’t been evaluated by the FDA, b) is a proprietary treatment method that costs as much as $10,000 cash up front (ACS isn’t covered by insurance) and c) is touted in the mass media, rather than in neurosurgical journals, as a miracle cure for a long-standing affliction.  That said, the science behind treatments like ACS is sound.

In order to understand how therapies like ACS combat DDD you must first understand the structure of an intervertebral disc (IVD).  The IVD is comprised of an inner nucleus pulposus (gel-like in consistency due to its combination of proteoglycans and type II collagen) and the outer annulus fibrosus (strong and fibrous like kevlar due to its type I collagen.) These inner layers are held together by cartilaginous endplates above and below (one patient recently told me that this looked like an ice cream sandwich to her; see figure 1.)  Various populations of cells within the IVD maintain the health of these structural components through the secretion of a perfectly balanced concoction of cytokines and growth factors.  At some point in adult life this delicate balance is disrupted in favor of so-called pro-inflammatory cytokines that promote the breakdown of the proteoglycans and collagens within the IVD.  Eventually the gel-like nucleus pulposus is replaced by firm, fibrous scar tissue (not a good shock absorber like the normal nucleus pulposus) and the annulus fibrosus tears and fails under the increased load.  This is DDD in a nutshell.  

Intervertebral disc  Cartilage cartilage defect torn cartilage cartilage degeneration sports injury orthopedics arthroscopy cartilage cell implantation chonrocyte implantation

Figure 1: Intervertebral disc with the inner gelatinous nucleus pulposus and outer annulus fibrosus. (Source: http://www.porcpotlas.hu/en/porckorong.html)

One of the pro-inflammatory cytokines that has been well-studied is interleukin-1 (IL-1).  Lab studies of human IVD cells show that IL-1 will stimulate the production of chemicals (matrix metalloproteinases if you’re interested) that break down components of the disc and will also turn off the genes that produce collagens and proteoglycans.  So if you’re a fan of disc health IL-1 is the bad guy.  Your body will keep IL-1 in check by concurrently producing a chemical that competes with IL-1 at its binding sites.  Let’s call this IL-1ra for IL-1 receptor antagonist.  In a degenerated IVD, as well as in other degenerated collagen-based tissues like knees and shoulders, IL-1 levels skyrocket while IL-1ra levels plummet so inflammation runs unchecked.  This is where ACS comes in.  In ACS, a patient’s venous blood is drawn and incubated in such a way that concentrates the levels of IL-1ra to levels that are 150 times normal levels (see figure 2).  The resulting serum is injected into the inflamed joints or into the spines of patients where IL-1ra combats the effects of IL-1 thereby halting inflammation and degeneration to relieve pain.  

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Figure 2: Schematic of the ACS treatment (source:  Wehling P, Moser C, Frisbie D, McIlwraith CW, Kawcak CE, Krauspe R, et al.: Autologous conditioned serum in the treatment of orthopedic diseases: the orthokine therapy. BioDrugs 21:323–32, 2007.)

Another therapy, platelet-rich plasma (PRP), also uses the patient’s own blood to combat degeneration of connective tissue.  PRP is thought to act by increasing the amount of local growth factors available to stimulate native cells to repair the degenerated tissue in the disc.  In summary, both ACS and PRP tip the balance in favor of repair and regeneration of the connective tissue of the degenerated disc.  

The data in support of the ACS treatment the strongest for orthopedic conditions such as tennis elbow and knee arthritis.  The data supporting the use of ACS in degenerative spinal conditions, however, is less clear.  In one double-blinded study (Becker et al, 2007) there was minimal increased benefit of ACS when compared to steroids for use in spinal epidural injections for radiculopathy (pinched nerve.)  I think that more randomized trials are needed to prove that ACS is superior to current treatments.  

While early data on these new biologic treatments is still mixed, the prospect of regenerative treatments for DDD and arthritis is very exciting.  Surely we’re just beginning to understand the importance of these interdependent chemical signals and how they relate to DDD.  I can’t help to think that someday, after treatments like these become mainstream, we’ll look back and wonder in astonishment about how we ever thought that a lumbar fusion, currently the gold standard for treatment of DDD, was ever considered a standard treatment at all!

Thanks for following along.  I know it was a complicated post!

J. Alex Thomas, M.D.

Sources:

Becker C, Heidersdorf S, Drewlo S, de Rodriguez SZ, Krämer J, Willburger RE: Efficacy of epidural perineural injections with autologous conditioned serum for lumbar radicular compression: an investigator-initiated, prospective, double-blind, reference-controlled study. Spine (Phila Pa 1976) 32:1803–8, 2007.

Le Maitre CL, Freemont AJ, Hoyland JA: The role of interleukin-1 in the pathogenesis of human intervertebral disc degeneration. Arthritis Res Ther 7:R732–45, 2005.

Masuda K, An HS: Prevention of disc degeneration with growth factors. Eur Spine J 15 Suppl 3:S422–32, 2006.

Wehling P, Moser C, Frisbie D, McIlwraith CW, Kawcak CE, Krauspe R, et al.: Autologous conditioned serum in the treatment of orthopedic diseases: the orthokine therapy. BioDrugs 21:323–32, 2007.

What is a Cervical Corpectomy?

In our last few posts we discussed anterior cervical discectomy and fusion (ACDF) as a treatment for cervical disc disease and spondylosis.  In ACDF a degenerated disc (or discs) is removed to decompress the spinal cord or a cervical nerve root.  In some cases, though, removing the disc alone is not sufficient to adequately decompress the spinal cord.  In these cases a corpectomy is performed in which the entire vertebral body as well as the adjacent discs are removed.  A corpectomy can be performed at just about any level of the spine.  In this post, though, we’ll discuss the use of corpectomy for pathology of the cervical spine.  

Again, in some cases of degenerative disc disease and spondylosis, ACDF alone is insufficient to adequately decompress the spinal cord.  For example, some patients with cervical spondylosis and stenosis will have osteophytes (fancy word for bone spurs) that form not only at the disc space (where they could be removed with a standard ACDF) but also behind the entire vertebral body (see figure 1).  Thus, a corpectomy is necessary to remove the osteophytes behind the vertebral body and decompress the spinal cord.

Cervical osteophyte

Figure 1. Sagittal T2 MRI of cervical spine demonstrating spinal cord compression from displaced cervical discs (red stars) as well as from large osteophyte behind vertebral body (red arrow.)  

Cervical corpectomy is also used in cases of trauma, tumor or infection in which the vertebral body has been destroyed.  This bony destruction may render the spine unstable.  In these cases the vertebral body is completely removed (along with the offending pathology) so that the spine can then be reconstructed and stabilized (see figure 2).

Cervical burst fx pngCervical burst fx png 1

Figure 2.  Left image is CT scan of cervical spine demonstrating C5 burst fracture (red arrow) in an adolescent male who dove into shallow water.  Right image is sagittal T2 MRI in same patient demonstrating fractured vertebral body (red arrow) and edema in spinal cord indicative of spinal cord injury (blue arrow.)  

The first steps of a cervical corpectomy procedure are identical to the steps of an ACDF (to review, click here).  Once at the spine the intervertebral discs above and below the vertebral body in question are removed.  After the discs are removed the vertebral body is removed with a high-speed drill; the bone dust is collected with a special suction trap to be used later as graft material.  Once the vertebral body has been removed and the spinal cord has been decompressed (after removal of the posterior longitudinal ligament) a spacer is sized to fit the defect left by the corpectomy.  As with ACDF these spacers come in a variety of shapes, sizes and materials.  I typically use a PEEK spacer (see figure 3) that is packed with the bone harvested from the corpectomy (or cadaver bone in cases of tumor or infection when the patient’s bone can’t be reused.) The risk profile is also similar that that of ACDF although the risks of dysphagia, vertebral artery injury and non-union (when the bones don’t fuse) are slightly higher for cervical corpectomy than for ACDF.  Length of hospital stay and recovery is typically the same as for ACDF.  

NIKO1

Figure 3. Polyetheretherketone (PEEK) spacer. (source: http://www.globusmedical.com)

In my practice I typically reserve cervical corpectomy for unique circumstances (i.e. tumor or trauma.)  In properly selected patients the outcomes are excellent.  See all of the steps of a cervical corpectomy that I performed recently in the video below.  

Thanks!

J. Alex Thomas, M.D.

 

What is an ACDF? Part II

What is an ACDF? Part II.

We have discussed the indications for anterior cervical discectomy and fusion (ACDF).  We have also discussed the evolution of the procedure from the days of Cloward to the modern ACDF today.  In this post we will discuss the steps of an ACDF.  Remember that surgeons can have different training experiences and skill sets.  Thus, there can be subtle variation in each surgeon’s technique.  This post describes the way that I do ACDFs but the general steps are the same no matter who you choose as your surgeon.   At each step I’ll discuss some of the possible risks of the procedure.  I apologize for the long post but I didn’t want to break up the steps of the procedure into two posts. Also, instead of using still images of an ACDF, I inserted a video at the end of the post of a one-level ACDF that I did recently.

After intubation, the patient is positioned supine (on their back) with a roll under their shoulders so that the neck is extended (tilted back.)  Some surgeons would work with a neuromonitoring technician who at this point would connect wires to the patient’s arms, legs and scalp to monitor somatosensory and motor evoked potentials (SSEP and MEP).  I won’t get into the details of SSEP and MEP but basically this allows the surgeon to monitor spinal cord function during the case; if there were any injury to the spinal cord during the case the monitoring technician could alert the surgeon.  This is not standard of care and is only an option for the surgeon to employ.  I typically do not use neuromonitoring on simple ACDFs as I think they add unnecessary cost and time to the procedure.  Also, I find the data very nonspecific and therefore not always that useful. 

I plan a small incision on the front of the left side of the neck, typically in a skin crease so that when the incision heals it’s barely noticeable (see figure 1).  I almost always make the incision on the left side of the neck in order to avoid the recurrent laryngeal nerve.  This nerve innervates some of the muscles of the vocal cords and if injured can cause hoarseness (about a 3% risk, and the hoarseness almost always resolves in a few months.)  The nerve takes a more unpredictable course on the right side so in my opinion it’s safer via a left-sided incision.  After the incision is I separate the platysma muscle (this is the only muscle that is cut during the procedure.)  Next, I gently dissect the natural tissue plane between the carotid artery and jugular vein laterally and the trachea and esophagus medially (see figure 2).  Injury to these structures is very rare (around 1/500) but patients can experience dysphagia (problems swallowing) because of trauma to the esophagus.  This occurs in 5-10% of cases (more common in multi-level ACDF) and, again, usually resolves in a few days.  After a bit of dissection I arrive at the front of the spine.  

 

 

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Figure 1: ACDF incision on left side of front of neck.

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Figure 2: Cross-section MRI of the cervical spine indicating ACDF approach.  The approach exploits a natural plane between the carotid artery (red) and jugular vein (blue) laterally and the trachea (yellow) and esophagus (green) medially.  

Once at the spine I mark the disc space with a needle to confirm that I’m at the correct level.  I’m careful to not disturb normal levels of the spine in order to avoid possible adjacent segment degneration later (the risk of which I quote at 10-15% after ACDF).  I then dissect the longus colli muscle off of each side of the spine.  This allows me to place a retractor along the spine that holds the soft tissue out of the working area.  At this point in the operation I will bring the operating microscope into the field (not all surgeons use the microscope but I find it useful.)  I then incise the annulus (outer casing) of the disc and begin removing the disc.  This is the disc material that is still in the disc space, not the material that is herniated or bulging.  Surgeons will use a few different types of instruments to remove the disc; I typically use a drill.  Eventually, after removing the bulk of the disc, I will arrive at the posterior longitudinal ligament (PLL) which is then removed.  At this point the dura (covering of the spinal cord) will be visible with its characteristic blue hue.  We can then see and remove any herniated disc fragments or bone spurs that are compressing the spinal cord or nerve roots.  It is during this decompression (or during placement of the spacer later) that more dreaded complications like neurological injury or paralysis can occur (very rare, occurring in less than 1/500 cases.)

Once the spinal cord and nerve root are decompressed I then scrape any remaining disc material off of the endplate of the vertebral body above and below the disc space. This is an important step that will allow for the growth of new bone (i.e. the fusion).  I then insert a spacer into the disc space.  These spacers come in many different types of materials, shapes and sizes but I’ll spare you the details on why one surgeon might choose one type of spacer versus another.  I prefer to use a spacer made out of synthetic materials such as PEEK or silicon nitride (see figure 3).  Prior to insertion I pack this spacer with graft material.  It’s this graft material that acts as the “seed bone” to promote the bony fusion across the disc space.  Some surgeons use the patient’s own bone (autograft) taken from the iliac crest (“the hip”).  While autograft is the best graft material, many patients complain of significant posteroperative pain at the donor site at the hip (more pain than the surgical site in the neck!).  Given this, I don’t use autograft from the iliac crest and instead use either cadaver bone or a stem cell product (allograft).  The spacer is carefully inserted using fluoroscopic guidance to ensure that it’s at the appropriate depth.  

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Figure 3: ACDF spacer (source: Amedica Corp.)

With the spacer inserted I move to the final step of placement of the plate.  In cases of one-level ACDF I don’t use a plate and instead use a spacer that allows me to secure the spacer in place using screws that pass through the spacer, a so-called standalone device (see figure 4).  Again, this is a matter of preference.  In multi-level ACDF I will use a titanium plate.  This is secured in place using small titanium screws (see figure 5). 

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Figure 4: Standalone ACDF spacer (source: Globus Corp.)

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FIgure 5: Titanium plate fastened to front of vertebral bodies with titanium screws (notice spacer in disc space). (source: Aesculap Corp.)

After all of the implants are in place I confirm that they are in good position with final xrays of the spine (see figure 6).  I then spend some time making sure that any points of bleeding are coagulated (another complication after ACDF is a hematoma in the neck causing airway compression and thereby requiring emergent re-operation, seen in less than1% of cases.)  I then close the platysma and the skin with suture (under the skin so that they don’t have to be removed) to complete the case.

Lateral ACDF Xray 1AP ACDF xray 1

Figure 6: Final X-rays after 3-level ACDF.

Despite the variations in technique and in the types of implants used, ACDF is almost uniformly successful with success rates exceeding 95%. 

Phew, that was a long post.  Thanks for hanging in there.  

J. Alex Thomas, M.D.

See all of the steps of an ACDF that you just read about here in this video: 

1. Fountas KN, Kapsalaki EZ, Nikolakakos LG, Smisson HF, Johnston KW, Grigorian AA, et al.: Anterior cervical discectomy and fusion associated complications. Spine (Phila Pa 1976) 32:2310–7, 2007.

2. Hilibrand AS, Carlson GD, Palumbo MA, Jones PK, Bohlman HH: Radiculopathy and Myelopathy at Segments Adjacent to the Site of a Previous Anterior Cervical Arthrodesis Radiculopathy and Myelopathy at Segments Adjacent to the Site of a Previous Anterior Cervical Arthrodesis *. J Bone Jt Surg 81:519–528, 1999.

3. Yang B, Li H, Zhang T, He X, Xu S: The incidence of adjacent segment degeneration after cervical disc arthroplasty (CDA): a meta analysis of randomized controlled trials. PLoS One 7:e35032, 2012.

4. Nassr A, Lee JY, Bashir RS, Rihn JA, Eck JC, Kang JD, et al.: Does incorrect level needle localization during anterior cervical discectomy and fusion lead to accelerated disc degeneration? Spine (Phila Pa 1976) 34:189–92, 2009.

 

What is an ACDF? Part I

In the last post we discussed the posterior cervical foraminotomy (PCF) in which a pinched cervical nerve is decompressed via small hole in the lamina at the back of the spine.  The main benefit of the PCF is that the nerve can be directly decompressed without significant alterations in the biomechanics of the spine (i.e. no alterations to the disc and no need for a fusion).   Most of the pathology that compresses nerves in the cervical spine, though, occurs in front of the nerve at the disc space and uncovertebral joint (see figure 1).  Thus, a major drawback of the PCF is that you only indirectly treat the cause of the nerve compression; you can’t remove the disc bulge or bone spur that is actually compressing the nerve.  Because of this and other limitations of posterior approaches, an anterior (i.e. from the front of the spine) approach was sought.

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Figure 1: axial view of the spinal cord in the cervical spinal canal.  Note the left side of the image where the nerve root is compressed from a herniated disc and overgrowth of the uncovertebral joint.  Notice how this pathology is found anterior to the nerve root.  (Source: Carette S, Fehlings MG. Clinical practice. Cervical radiculopathy. N Engl J Med. Jul 28 2005; 353(4): 393-399.)

In the 1950s Cloward as well as Smith and Robinson described similar techniques for an anterior approach to the spine for removal of herniated discs or bone spurs.  Both Cloward’s and Smith/Robinson’s techniques involved the insertion of bone into the disc space after removal of the disc (i.e. discectomy) to promote a fusion across the disc space (the term fusion refers to the formation of bone that causes two bones, in this case vertebral bodies, to fuse into one.)  Thus, this technique came to be known as an anterior cervical discectomy and fusion, or ACDF.  Shortly thereafter other surgeons altered the technique such that it only involved the discectomy without the additional step of inserting the bone graft.  This technique is referred to as an anterior cervical discectomy without fusion (ACD.)  Since then, there have been several decades of controversy in the literature about which of these therapies (ACD versus ACDF) is superior.  The advent in the 1980s of plating the front of the spine during an ACDF (the plate acts as an internal brace to theoretically promote more rapid bony fusion) only added to the controversy.

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Figure 2: Image from Cloward’s 1958 article describing his ACDF technique.  Label c indicates the path of the large-bore drill used to drill away the disc en route to the spinal cord and nerve root. This hole was then filled with a bone plug.  (Source: Cloward RB. The anterior approach for removal of ruptured cervical disks. J Neurosurg. 1958; 15: 602–17.)

Despite the controversy, what is certain is that the modern ACDF, with its plate, spacer and bone graft materials (see figure 3) is much costlier than the simple ACD.  While the surgical approach hasn’t varied much, the materials definitely have.  For example, these days more exotic materials are used to make the spacers to try to make them promote fusion.  Also, because of pain associated with harvesting bone graft from the hip many surgeons today will use manufactured graft products rather than the patient’s own bone.  The cost of all of these new materials starts to add up.

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Figure 3: Side view of cervical spine after modern 2-level ACDF.  Removed discs have been replaced with spacers and bone graft (red arrows). A plate is attached to the front of the vertebral bodies with screws.  (Source: Medtronic.com)

Why incur the cost then? Why not just offer patients the ACD, which by most studies in the literature is just about as effective as ACDF?  First, most surgeons believe that by using a spacer they can provide more structural support to the spine to restore disc height (degenerated discs often collapse which can exacerbate narrowing around the nerves).  Also, some studies found that after ACD (without the spacer and fusion) there was a significantly higher rate of kyphosis (a deformity in which the spine bends forward over time) when compared to ACDF.  Is it worth the extra cost of the spacer to avoid this potential complication down the road? Second, regarding the plate, many surgeons, myself included, believe that the extra stability of the plate promotes fusion more rapidly and effectively.  This, in my practice at least, allows the patient to go home without having to wear a neck brace.  What is it worth to the patient to not have to wear a brace for 2 months?   Finally, all of these modern devices are supposed to make the bones fuse together more effectively.  Again, there has never been any strong evidence to suggest that fusion is mandatory for the patient to feel better after a cervical discectomy.  That said, most surgeons believe that movement at the disc space causes bone spur formation and disc bulging and that by performing a fusion the surgeon arrests this degenerative process (at that level of the spine at least; see my post on adjacent segment degeneration).  If the goal is to maximize the patient’s chances of fusion is it worth the cost of all of these implants to increase the rate of fusion from, say, 90% to 95%? These are difficult questions that we’ll never be able to answer in a blog post.  It is always worth considering, though, that just because a treatment is more modern and more costly doesn’t necessarily mean that it is better than the treatment that’s been around for decades.

Wow, I got off on a healthcare economics rant there…  In the next post we’ll discuss the steps involved in an ACDF.

J. Alex Thomas, M.D.