Medical Device Daily Contributing Writer

Late last month, a surgical team at The Spine Institute at Beth Israel Medical Center (New York) performed a live surgical demonstration of replacement of a degenerated spinal disc with an artificial one.

The SB Charité Artificial Disc from the DePuy Spine (Raynham, Massachusetts) unit of Johnson & Johnson (New Brunswick, New Jersey) was approved for use in the U.S. by the FDA in October (Medical Device Daily, Oct. 28, 2004). Approval is limited to the lower lumbar discs — L₄-L₅ and L₅-S₁.

DePuy Spine acquired rights to the Charité in June 2003 when it bought Link Spine Group (Branford, Connecticut) for $325 million (MDD, June 5, 2003).

Fabien Bitan, MD, orthopedic surgeon and principal investigator for the SB Charité clinical trial at The Spine Institute, performed the disc replacement procedure with the help of Scott Hannon, MD, a general surgeon. John Hertzog, MD, served as moderator of the webcast.

As Hertzog explained, “Americans work hard and play hard, and as a result, more than 75% of Americans suffer from back pain at some point in their lives. Young people push their bodies at the gym and on the fields, and baby boomers are opting to continue being active as they get older.“ As a result of this trend and emerging medical technology, he said, “joint replacement surgeries of the knee and hip have become commonplace, yet many people live with and tolerate back pain.“

Hertzog said these back pain sufferers now have “a new treatment option. An emerging type of spinal surgery, called total disc replacement, has shown great promise in clinical trials.“

The Charité disk includes two metal endplates and a core of formed polyethylene. It is offered in four sizes, allowing customized fit for each patient.

Bitan's patient in the webcast procedure was a 36-year-old female who had suffered intense back pain for 2-1/2 years. Conservative therapies were unsuccessful in relieving her pain. Radiological studies confirmed her L₄-L₅ disc had degenerated and no longer supported her spine normally. As a result, spinal nerves were under pressure, causing her almost constant pain, he said. Bitan elected to replace her degenerated disc with the Charité disc.

With the patient anesthetized and in the supine position, Hannon accessed the front of the lumbar disc using an abdominal approach. He was careful to remain outside the peritoneum, avoiding the major blood vessels in front of the spine. Once the front of the vertebra was exposed, Bitan took over and removed the degenerated disk in the traditional manner using pituitary and Kerrison rongeurs. He took care to remove the entire disc, then prepared the space by cleaning the proximal and distal vertebral edges with bone-removing devices. A lamina spreader kept the disc space open during this part of the procedure.

“It is essential that the space be smooth and free of extraneous tissue so the artificial disk will fit tightly and support the spine in the same manner as a normal disc,“ Bitan noted.

A laparoscope and camera provided live views of the cleared space. Bitan took care to avoid the spinal canal that sits directly behind the disk space. After the disc space was cleared, the implant's endplates were placed and firmly malleted into the prepared vertebral surfaces. Then a proprietary template, or sizer, was used to determine which size implant should be used. Finally, the appropriately sized core was placed. After fluoroscopy confirmed the angle and centering of the device, Bitan removed the spreader and the wound was closed in the typical manner for an abdominal surgery.

Herzog reviewed the involved anatomy for the web audience. “The human spine consists of 33 interlocking bones [vertebrae] separated by shock-absorbing bundles of tissue, which can be damaged or degenerate over time,“ he said.

He noted that the most common treatment for a degenerative disc is spinal fusion surgery, “which involves removing the disc and bridging the adjacent vertebrae with a piece of bone, usually grafted from the patient's own hip.“ More than 200,000 spinal fusions are performed each year.

Although fusion is generally effective in eliminating pain, the procedure has its drawbacks. By replacing a flexible disc with hard bone, it creates a section of immobility on that portion of the spine, which can further stress adjacent discs. This may be the reason that some people experience recurrent back pain years after having a fusion procedure.

Total disc replacement is appropriate for treatment of degenerative disc disease, Bitan said. It is not indicated, however, in patients with scoliosis, herniated discs, previous spinal fusion or deformity/curvature of the spine. He noted that patients also need strong, dense bones to hold the end plates in place. This means surgical candidates tend to be younger, non-smoking and more active.

Bitan said the SB Charité Artificial Disc is one of the most popular artificial discs among European spinal surgeons, who have been using several such prosthetic discs since the 1980s. Their patients have experienced relief of pain and restored mobility, he said.

While serving his residency in France, Bitan took part in the first artificial disc surgery with the current version of the disc in that country in 1986. He said he performed dozens of the procedures during the 1980s and 1990s.

It was noted during the webcast that The Spine Institute of New York at Beth Israel is one of the FDA investigational sites for the procedure and will serve as the training ground for New York-area spine surgeons who want to learn the Charité technique.

According to Bitan, in the hands of an experienced spinal surgeon the lumbar disc replacement procedure takes less than two hours. Patients report immediate relief from the pain and many up are up walking around a few hours after surgery. He said that some of his patients have gone home the same day.

What is most important, he noted, is that patients are restored to full spinal mobility with a normal range of motion — something that it is not experienced with spinal fusion,

Concluding the webcast, Bitan said that artificial disc replacement is not for everyone, “but I do think it's the future.“

He added: “We're really getting into a new era in spine surgery and it's very exciting.“