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Five-Year Study: Comparing Lumbar Artificial Disc Replacement to Spinal Fusion in Patients with Degenerative Disc Disease

December 13, 2017
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To assess the longevity, effectiveness, and safety of artificial disc replacement (ADR), also known as total disc replacement (TDR), a team of authors which included Dr. Jack Zigler, orthopedic spine surgeon at Texas Back Institute in Plano, Texas, and Dr. Matthew Gornet an orthopedic spine surgeon at Orthopedic Spine Center of St. Louis and Cornerstone Research team conducted a meta-analysis of the available randomized controlled trials with published five year outcomes comparing ADR to spinal fusion.

The patients were those diagnosed with chronic lower back pain from single-level lumbar Degenerative Disc Disease (DDD). Here's what you need to know.

The Introduction

Lumbar Degenerative Disc Disease (DDD) is a frequent cause of severe lower back pain. In roughly 62 percent to 84 percent of DDD patients, low back pain becomes chronic (defined as pain lasting longer than 12 weeks). Whereas acute pain is a normal response that warns us of possible injury, chronic pain can last for months or years.

Patients who have had unrelenting lower back pain symptoms for longer than six months and have had conventional treatments fail to relieve their chronic back pain symptoms may be a candidate for artificial disc replacement (ADR) also known as total disc replacement (TDR) as opposed to spinal fusion, the former gold standard in spine surgery.

What is a Spinal Fusion

Spinal fusion surgery is a treatment performed by a spine surgeon that permanently fuses two or more vertebrae in the patient's spine, which reduces excess motion that causes chronic back pain.

Spinal fusion uses techniques intended to impersonate the patient's natural healing process of broken bones. During spinal fusion, the surgeon places bone or a bone-like substance within the space between two spinal vertebrae. Metal plates, screws, and rods are used to lock the vertebrae together with the goal of uniform healing.

Exceeding the immediate dangers of this (and any) surgery, spinal fusion, according to the doctors at the Mayo Clinic, immobilizes parts of the patient's spine and changes the spine’s movement by placing additional stress on the vertebrae above and below the fused portion. This may increase the rate degenerate in a patient’s spine, which can generate more damage and maybe chronic pain.

While fusion rates and efficiency results have advanced in recent years, more than one-third of post-fusion patients still experience painful symptoms, which can lead to a second or third operation.

What is Artifical Disc Replacement

The purpose of artificial disc replacement (ADR) is to help relieve a patient's chronic back or neck pain and advance mobility in those with chronic lower back (lumbar) pain. ADR decompresses the patient's spinal cord and protects the natural movement of the patient's neck, spine, and back.

Approved by the U.S. Food and Drug Administration (FDA), ADR is a form of arthroplasty (the surgical reconstruction or replacement of a joint) performed by a spine surgeon, which involves replacing any degenerated intervertebral discs in the patient's spinal canal with an artificial one. Normally, this is done in the lower back or the neck (cervical spine).

The purpose of artificial disc replacement surgery is to stabilize the patient's spine while preserving the patient's natural movement of range and motion. The artificial disc used for artificial disc replacement (ADR) allows the patient to move freely without pain or strain while supporting the spine's natural range of motion with increased flexibility.

The Method

The author's examined all of the trial results between patients who underwent ADR surgery with those patients who had spinal fusion in single-level lumbar DDD and their 5 year outcomes using data from PubMed and Cochrane Central Register of Controlled Trial's medical directories.

Using well-respected statistical methods, the authors pooled together the evidence from the four studies to be able to make broader, higher impact conclusions about how ADR stacks up to fusion in the long-term. Based on the Discussion section of the manuscript, the authors were not surprised at the strength of the results in favor of ADR.

The outcomes involved included these measurements:

  • The Oswestry Disability Index (ODI). A tool doctors use to measure a patient's permanent functional disability. Patients answers questions in 10 sections, which are each scored separately (0 to 5 points each) and then totaled — the maximum score of 50. The lower the number, the less pain the patient experiences.
  • Back pain scores. Used to find the mean change in the patient's back pain score from before surgery up until the five-year follow-up period.
  • Patient satisfaction. Scored to test the patient's willingness to choose the same surgery again.
  • Reoperations. Examined and defined as device-related failures resulting in the subsequent surgical interventions of a reoperation, revision, removal, or supplemental fixation. Was a second surgery needed?
  • All surgeons who perform ADR are required to report product problems, if they learn any of their devices may have caused or contributed a death or serious injury. This is known as Device-related serious adverse events (SAEs), which was also examined during the five-year follow-up period.

All investigations from the four analyses were managed using a random-effects model, also called “mixed models” or “variance components models.” These models allow for a patient’s individual characteristics to be considered rather than pooling their results into an average sum with other candidates. This removes any biases and allows the result to be a real variation notating biological and environmental factors rather than just an analytical trick to test the variability of patients’ surgical responses.

Analyses were reported as relative risk (RR) ratios and mean differences (MDs). Sensitivity investigations were administered for different outcome definitions, high loss to follow-up, and high heterogeneity (diverseness).

The Results

The meta-analysis incorporated four randomized controlled trials reporting on the 5 year outcomes of ADR versus fusion testing the five outcomes above. The results included:

ODI success – ADR was shown to be statistically better than fusion.

ADR patients were more likely to have a clinically relevant improvement in their ODI scores than fusion patients at 5-years (p = 0.05)

Back pain scores – ADR was shown to be numerically but not statistically better than fusion.

There was no affiliated improvement in any patients’ back pain scores whether the DDD patient received lumbar ADR or a spinal fusion during the five-year follow-up (p = 0.25)

Patient satisfaction – ADR was shown to be statistically better than fusion.

Patients reported greater satisfaction with an implanted ADR device rather than spinal fusion during the five-year follow-up (p = 0.01).

Reoperations – ADR was shown to be statistically better than fusion.

Patients who received ADR had a lower risk of reoperation (p = 0.002).The need for reoperations resulting from device-related malfunctions was consistent in all four studies. Treatment of lumbar DDD with ADR produced a 48 percent decrease in the chance of reoperations as compared to treatment with spinal fusion.

The Quality

All four studies showed the same risk for bias. As per sound statistical methods, the authors completed sensitivity analyses to control for any potential bias in the studies. 

Doctor reviewing spinal x-ray.

All of the studies were randomized meaning the surgeon investigators who implanted the devices did not know if the patient would be receiving fusion or ADR until after the patient was selected.

The Conclusion

Based on the study's evidence, Degenerative Disc Disease patients who underwent lumbar disc replacement saw long-term strides in pain relief and motion preservation making ADR a beneficial alternative treatment to spinal fusion.

The authors concluded that, "ADR is an effective alternative to fusion for lumbar DDD. It offers several clinical advantages over the longer term that can benefit the patient and reduce health care burden, without additional safety consequences."

Takeaways

  • When compared with conventional treatments, such as physical therapy, exercise, activity limitation, and medicational pain management, ADR exhibited equal if not higher positive results at five years.
  • Choosing ADR decreases the patient's chances of any adjacent discs degenerating further increasing the patient's chances of reoperation without pain relief.
  • Patients in the meta-analysis who underwent ADR were notably more likely to be satisfied with their treatment option at five years.

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