Nucleus Replacement: Perspectives Regarding the Gap in the Continuum of Spine Care and Degenerative Disc Disease

Confucius said, “Do not use a cannon to kill a mosquito.” In spine, the admonition could become, “Do not use fusion to treat an early stage degenerated disc.” Nucleus replacement may become an alternative to more invasive procedures in cases of early stage degenerative disc disease. These technologies may fill part of the gap in the continuum of spine care and also help abate the use of the controversial “cannon,” otherwise known as fusion. After all, Confucius had a good point!

The Gap in the Continuum of Care

Back pain is treated along a continuum of care, ranging from conservative therapies to invasive surgical procedures. Conservative treatments traditionally include exercise regimes, NSAIDs, physical therapy, and steroidal injections. Conservative treatment focuses on pain management, and it is generally recommended for at least six months prior to surgical intervention.

Surgical intervention can include procedures ranging from percutaneous microdiscectomy to invasive multi-level fusion. A discectomy is often performed to remove a part of, or the entire, disc in order to relieve pressure on the nerve. The basic goal in decompression procedures is to reduce or stop the pain by taking pressure off pinched nerves. With respect to fusion, the segment that is causing the pain is immobilized by fusing two or more vertebrae together. Posterolateral fusion remains the “gold standard” in fusion. Chart 1 is an analysis from the PearlDiver Patient Records Database showing the various approaches to spine fusion. Of note is that fusion is most common in the lumbar region. The lumbar region is the target for many emerging nucleus replacement technologies. In the broader context, the cervical and lumbar regions are also the regions of focus for TDR (total disc replacement) technologies.

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Chart 1: Spine Fusion by Approachspine fusion chart
Source: PearlDiver Patient Records Database (2004-2006)

The gap in care exists in two areas. The first is between conservative treatments and the decompression procedures mentioned previously. Currently, if conservative treatments prove ineffective, the patient may have to resort to having either the lamina or all or part of a vertebral disc removed surgically, or both. It is also important to note that these treatments are not reversible. So, there remains a treatment where patients must choose between non-surgical pain management techniques and invasive, irreversible, surgical procedures. While percutaneous techniques and MIS technology continue to evolve and gain surgeon acceptance, the end result is still the removal of the native disc or bone, or both.

The second gap falls between the “ectomies” and fusion. This gap is being filled with technologies such as total disc replacement and facet replacement technologies. While facet replacement technologies have not yet been FDA approved for use in the United States, innovative ideas continue to surface. Indeed, at the standing-room-only facet joint seminar last October before the 2007 North American Spine Society annual meeting, “The Science of Facet Joint Repair and Total Posterior Arthroplasty” by Robin Young, the prospect of combining facet replacement and artificial disc technologies was on the radar of surgeons. This combination is premised on the idea that these technologies, applied alone, will not solve the problem of back pain. Rather, a comprehensive approach has been put forth involving the disc, facet joints, and stabilization. Wall Street estimates that total disc replacement is a $1.5 billion market opportunity composed of $600 million for lumbar and $900 million for cervical discs. The facet replacement market has been estimated at nearly a half-billion dollars. However, a note of caution is in order here, as regulatory and reimbursement challenges could markedly slow the adoption of these technologies.

Target: Fusion

According to Orthopedic Network News (Vol. 18, October 2007), over 500,000 fusions were performed in 2006, representing 50% of all inpatient spinal procedures. Fifty-four percent of fusions performed were thoracolumbar fusions. These numbers are also echoed in the PearlDiver Patient Records Database, where lumbar fusion is the most common, making up 47% of all fusions in the population under 65 years of age.

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Were these fusions all necessary? This is a topic for another article, or perhaps an entire book! In short, it is generally believed that there will always be a market for fusion as it relates to deformities or instability in the spine. There will also be a place for fusion with respect to trauma or fractures. The question moving forward revolves around the role that fusion will play in treating early stage spinal disorders such as degenerative disc disease (DDD) or disc herniation. In his book entitled I’ve Got Your Back, The Truth About Spine Surgery, Straight From a Surgeon, Dr. Nathaniel Tindel related that “I have to conclude that, if you have back pain, your chance of getting better with fusion is about the same as your chance of getting better with an effective, nonoperative treatment program.” This statement is relevant as we consider the potential market for an alternative treatment such as nucleus replacement.

Fusion is the bread and butter with respect to spine industry revenues. In fact, fusion adjuncts and interbody devices make up close to 60% of spine industry revenues, which amounts to over $3 billion! Should nucleus replacement improve outcomes and become accepted as a cost-effective treatment for early stage degenerative disc disease, many of the fusions currently performed may not be necessary. Wall Street estimates that the nucleus replacement market could generate over $2 billion in revenues by 2014. Nucleus arthroplasty could dramatically shift the revenue mix in the industry, as more money is spent on early stage treatment of spine disorders. Currently, most spine industry revenues are realized at the end of the continuum of care. In the future, we may see revenues shifting more towards early stage treatments and preventative treatments, causing a move away from fusion.

“Study the past if you would define the future” – Confucius

Nucleus replacement is not new. However, the improved techniques and materials have restored interest. Let’s start at the beginning. According to, nucleus replacement has its roots in the 1950s. Here’s the skinny on the beginnings of nucleus arthroplasty.

* 1955: David Cleveland injected methyl-acrylic into the disc space of discectomy patients
* 1959: Paul Harmon inserted Vitallium spheres into the disc space
* 1964: The Fernstrom ball is implanted to replace a disc in the lumbar spine

In short, the ideas of total disc replacement and nucleus replacement are not new, but current technology, which will be the subject of part 2 of this article, may prove to be the most promising. A long time in coming!

Nucleus Replacement: A Possible Solution to Early Stage DDD

Nucleus replacement seeks to fill the first “gap” mentioned above between conservative treatments and what are essentially decompression procedures.

In contrast to total disc replacement, nucleus arthroplasty replaces the nucleus pulposus and restores disc height, while leaving the endplates and annulus intact. Indications for nucleus replacement include patients diagnosed with single-level degenerative disc disease or central herniation, or for use as a prophylactic at the same level after a discectomy or at the adjacent vertebral level. Nucleus arthroplasty may become an adjunct to a discectomy in the future. In the Spine Technology Handbook (page 287), Dr. Steven Kurtz and Dr. Avram Edidin related that “if one could replace the nucleus of a patient earlier on in the degenerative process―where there has been a loss of hydration of the nucleus but a relatively intact annulus―the chance of repressurizing or tensioning the annulus fibrosis may limit or eliminate the mechanical consequences that may be responsible for further degeneration of the annulus.” Nucleus replacement may also serve as an alternative to those patients who are not potential TDR candidates or who feel TDR is too aggressive.

The overall goal of nucleus replacement is also of importance. There is still much debate about the exact source of lower back pain. This holds true for discogenic pain. In his book, Dr. Tindel related that “We don’t know for sure how discs (unless they’re herniated and pressing on a nerve) cause pain, or whether a particular disc is the culprit.” We know that nerve impingement can lead to sciatica and radicular pain and that there is mechanical pain associated with disc degeneration. The question revolves around whether nucleus replacement should restore disc height, or intradiscal load, or both?

Additional advantages to nucleus replacement include shorter operating times, minimally invasive procedures, and a focus not only on motion preservation, but also on anatomy preservation. In an article published at entitled “Disc Nucleus Replacement as an Alternative to Artificial Disc Replacement,” Dr. John Sherman related that “Replacing the entire disc through artificial disc replacement surgery is an extensive and technically demanding operation which can involve removing the endplates (the cartilage between the vertebral bone and the disc), a large part of the outer portion of the disc (the annulus), and the complete inner portion of the disc (the nucleus).” Dr. Sherman also makes the point that since nucleus replacement can be performed via the same approach as a discectomy, there is less scar tissue after the surgery, which is an advantage should a revision or another surgery in the same area be necessary.

Degenerative Disc Disease and Nucleus Arthroplasty

The PearlDiver database zeros in on the patient population under 65 years of age, making it ideal for market analysis with respect to technologies treating early stage spinal disorders. Lumbar degenerative disc disease is the most common spine diagnosis in the PearlDiver Patient Records Database, followed by lumbar disc herniation. Degenerative disc disease was more common in females than males, 54.3% versus 45.7% of diagnoses, respectively. Common associated diagnoses include lumbago, thoracic or lumbosacral neuritis or radiculitis, and disc herniation.

Table 1 is an age group breakdown by gender of degenerative disc disease from the PearlDiver database. The percentages represent diagnoses in patients under 65 years of age. The widely accepted Kirkaldy-Willis model of the degenerative cascade describes three stages of disc degeneration. The first stage (highlighted in red below) occurs between the ages of 20 and 30 and can result in early stage soft tissue damage to the annulus and nucleus. The second stage (highlighted in yellow below) typically occurs between the ages of 30 and 60 and is known as the stage of instability. In the second stage, disc height can be lost due to increasing loads on the intervertebral disc. The third stage (highlighted in green below), commonly seen in patients over 60, is known as stabilization and can be characterized by further extreme degeneration and narrowing of the disc height, as well as endplate irregularities.

Based on the table below, it can be seen that the majority of degenerative disc disease diagnoses occur during stage 2 or early stage 3. In fact, in the population under 65 years of age, 51.7% of the diagnoses occur in women between the ages of 50 and 64, during stages 2 and 3. Part of the future success of nucleus replacement could be catching potentially asymptomatic early stage degenerative disc disorders. Based on PearlDiver data, many DDD diagnoses occur in the later stages, which could imply that nucleus replacement is not an option for these patients.

Table 1: Distribution of Degenerative Disc Disease Diagnoses DDD Diagnosis
Source: PearlDiver Patient Records Database (2004-2006)

Table 2 is based on an analysis of primary inpatient procedures performed when lumbar degenerative disc disease was the primary diagnosis. Lumbar fusion remains the standard of care. In fact, TDR devices made up less than 1% of the procedures performed in the U.S. during 2004-2006.

Table 2: Primary Inpatient Procedures Performed in Response to DDDprocedures in response to DDD
Source: PearlDiver Patient Records Database (2004-2006)

Nucleus Replacement: From the Cannon to the Nucleus

Nucleus replacement is an intriguing technology that could potentially fill part of the gap in the spine continuum of care. Nucleus replacement products are designed to treat early stage degenerative disc disease, which is one of the most common spine disorders in the population under 65 years of age. This, combined with an increasing desire to move away from invasive, motion limiting procedures such as fusion, and a growing patient base in an aging population, may propel this technology to the forefront of spine. Nucleus replacement could help redefine the continuum of care by broadening the focus to include not only early diagnosis of degenerative disc disease, but also a reduction in the need for surgical procedures performed further down the continuum of care.

Written by Matt Menze, PearlDiver Spine Analyst