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Many reasons why lumbar artificial disc replacement never achieved expected prominence

ByJohn C. Liu, MD

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When the Charité artificial disc received FDA approval for clinical use in 2004, most spine surgeons thought lumbar artificial disc replacement was going to change spine surgery. They believed the issues of adjacent-level degeneration and reoperations would be issues of the past and this new, exciting technology offered the ability to maintain normal motion in the lumbar spine, which sounded natural and how things should be, instead of creating a rigid lumbar segment.

John C. Liu

At the time, the thought was that spine surgery was going in the direction of hip and knee surgery, where motion- preserving devices and not fusions were the future. However, with time and experience, it seems that lumbar artificial disc replacement (ADR) has never fully achieved the expectations most spine surgeons initially had. The questions as to why lumbar spine ADR did not follow the paths set forth by hip and knee motion preservation devices to become the “norm” for patients has always intrigued me. Is spine that much different than other joints in the body?

As it turns out, the reasons why lumbar spine ADR never achieved the expected spine prominence might be multiple. In the beginning, it became clear that the indication for lumbar ADR was quite narrow and the data of superiority to lumbar fusion was not conclusive. Patients have to have mechanical back pain due to primary lumbar disc degeneration without other common causes of back pain, including spondylolysis, spondylolisthesis and facet arthropathy. Patients also need to be relatively young in age, and not have a history of prior fusion surgery and osteoporosis.

There was also disagreement if ADR at L5-S1 really made sense with the limited amount of motion that naturally occurs there. It just happens that L5-S1 is also one of the most common lumbar segments that undergoes degeneration. In my practice, if all the limitations for lumbar ADR were included, lumbar ADR would account for less than 1% of all the patients I see.

Other reasons why lumbar ADR was slow to be adopted include reimbursement questions. This was a major issue when ADR first appeared and still continues to be an issue today. Approval of an ADR often requires spine surgeons and patients to go through multiple layers of appeals. Even with the appeals, ADR surgery is oftentimes denied. It has become more difficult to even have lumbar fusions be approved, let alone lumbar ADR, where insurance companies often consider it an “experimental surgery.”

For most spine surgeons, gaining anterior access requires an access surgeon. This is often a vascular surgeon because of the number of large vessels that need to be mobilized to gain the amount of anterior disc space exposure required to properly implant lumbar ADR devices. The corridor required for ADR is significantly wider than what is required for anterior lumbar interbody fusion (ALIF). An experienced access surgeon may be able achieve a reasonable access for an ALIF, however, access may not be adequate for proper insertion of a lumbar ADR implant, especially at L4-5 where more vascular mobilizations are required. The surgeons’ learning curve for lumbar ADR definitely is steeper for both spine surgeons and access surgeons.

The anterior access to the spine also becomes a major issue when revision surgery is required. With prior surgery in the anterior corridor, any attempt to re-expose the same level often carries significant morbidity and even mortality due to the adhesions of the vascular structures within the vicinity of the ADR. Revision ADR requires an experienced vascular surgeon to work in this potentially hostile environment. Vascular surgeons who are experienced enough to tackle this difficult problem are few, and they are not always available in any hospital setting. With the relatively limited number of lumbar ADRs, especially revisions, being performed, the expertise gained may be for a dying breed of surgeons going forward. Will there be enough young vascular surgeons who are adequately trained to perform this difficult task in the future?

As spine surgeons, perhaps the thought of difficulty in revision surgery for lumbar ADR affects how we render a decision to select a particular operation for patients. Innately as surgeons, we want to be able to fix the complications we create. With ADR, the reliance on another surgeon to get us to the problem with all the associated potential risks that come with the revision negatively affects our decision to offer lumbar ADR as a surgical option. The balance of the benefit compared to the risks, especially taking into account the potential for revision surgery, will often move spine surgeons away from recommending lumbar ADR as a surgical choice.

Interesting enough, cervical ADR appears to be increasing as an alternative to anterior cervical fusion surgeries. The indications may be broader than for lumbar ADRs and insurances usually offer coverage for most single-level procedures. More importantly, revision ADR in the cervical spine is relatively straightforward and does not place the patient in significant harm’s way. Having performed several ADR revisions, the surgery is similar to a revision anterior cervical fusion and does not require an access surgeon to approach. There are no life-threatening complications. Cervical ADR does not carry the potential high morbidity or mortality that a lumbar ADR does and most spine surgeons would be more inclined to offer it to patients as an alternative to cervical fusion or foraminotomy.

With my experience, would I want a lumbar ADR if I had mechanical back pain attributed to an isolated lumbar degenerative disc at L4-5 without spondylolisthesis, spondylolysis, osteoporosis and facet arthropathy? I would say, “Probably not.”