ProDisc Superior to Fusion

So says my doctor: Dr Delamarter

Surgeons and patients hoping to preserve the natural mobility of the spine through total disc replacement (TDR) now have a second option according to new research being unveiled this week at the North American Spine Society’s (NASS) 21st annual meeting in Seattle. In a pivotal FDA-regulated trail, the ProDisc-L artificial disc proved superior to spinal fusion for the treatment of back pain related to disc degeneration.

Newswise — “The ProDisc artificial disc is the first motion-sparing technology ever shown to be superior to fusion,” said NASS member Rick B. Delamarter, MD, of the Spine Institute at Saint John’s Health Center in Los Angeles.

“There will always be a role for fusion to treat problems such as deformity, severe facet arthritis, and instability,” he added. “But the whole pendulum is shifting to nonfusion technology.”

According to criteria developed by ProDisc’s maker Synthes, the overall success rate among patients who received the ProDisc was 64%, compared to 45% among those who underwent circumferential (360-degree) fusion. Some 94% of ProDisc patients had normal motion (mean 7.7 degrees).

By stricter FDA standards, success rates were less impressive – 53% in the ProDisc group and 41% in the fusion group. The FDA analysis acknowledged that ProDisc led to greater patient satisfaction and overall success than fusion, but found no advantage for ProDisc in disability and pain reduction. The FDA concluded that the ProDisc “is reasonably safe and effective.”

Whether a motion-sparing artificial disc becomes the dominant treatment for patients with symptomatic disc degeneration remains to be seen. Third-party payers have been resistant to paying for TDR based on perceived gaps in the evidence about its long-term safety and effectiveness and a lack of evidence comparing TDR to nonoperative care.

Like other artificial discs, the ProDisc was designed to overcome limitations inherent in fusion. The new study demonstrated that the ProDisc preserves the natural mobility of the spine, eliminates the need for bone grafts, and limits the collateral damage associated with posterior surgical approaches. Clinical trials have not yet shown another hoped-for benefit of artificial discs – that they can prevent degeneration of adjacent vertebral segments.

The ProDisc is the second artificial disc to win FDA clearance. The Charité artificial disc, made by Johnson & Johnson, was approved in October 2004 on the basis of a noninferiority trial showing that outcomes of the Charité device were no worse than those of fusion with a BAK fusion cage.

The new ProDisc study went further. It was also designed as a noninferiority trial, but included a secondary superiority analysis showing that the overall success rate of ProDisc was not only no worse than fusion’s, but better. The FDA approved the ProDisc on August 14, 2006.

The ProDisc is comprised of a polyethylene central core sandwiched between two metal endplates. Unlike the Charité disc, which is designed with a free-floating central core, the ProDisc is a semi-constrained prosthesis with a keel intended to lend stability and minimize device migration and subsidence.

Delamarter and colleagues randomized 242 men and women with back and/or leg pain to the ProDisc (162 patients) or fusion (80 patients), then followed them for two years. Patients had previously failed at least six months of nonoperative care, demonstrated radiographic evidence of single-level degenerative disc disease, and scored greater than 40% impairment (> 20/50) on the Oswestry Disability Index. Their average weight was 176 pounds and their average age was 39 years.

According to the analysis by Delamarter et al., patients in both groups had similar pain and disability through postoperative month 18, but ProDisc patients reported significantly less pain and disability at the 24-month point. The findings appear to be at odds with the FDA analysis.

Complication rates were similar between groups, and no patient in either group suffered a major complication. About 4% of ProDisc recipients had reoperations, compared to 5% of fusion patients.

Delamarter emphasized that 81% of ProDisc patients said they were satisfied with the treatment, compared to 69% of fusion patients.

He pointed out that the stringent FDA success criteria did not include patient satisfaction. “We’re in the business of improving quality of life. The FDA’s determination of success is a mathematical formula. It isn’t a patient success formula,” he said.

The FDA in the conclusion to its summary said the trial “demonstrated that the ProDisc-L Total Disc Replacement is reasonably safe and effective by demonstrating its noninferiority when comparing Overall Success and adverse event rates to the control for the studied indication.” Other statistically significant advantages observed in the ProDisc group--diminished blood loss, surgery time, and hospital stay – may not have been clinically significant, according to the FDA analysis.

The future of ProDisc in many ways lies in the hands of third-party payers. Though payers have expressed strong reservations about the Charité disc, it is unclear how they will respond to the ProDisc.

Questions remain about the long-term durability of artificial discs. Laboratory studies suggest the ProDisc will last 40 to 50 years, said Delamarter. “But what happens clinically at 30 to 40 years we don’t know,” he acknowledged. The FDA license requires Synthes to follow patients in the trial for a total of five years.

Some observers wonder if broader use of the technology might result in worse outcomes. FDA-regulated device trials typically employ some of the best surgeons in the field. Whether future ProDisc outcomes will be comparable, better, or worse than those documented in the FDA trial is unknown.

Delamarter believes the ProDisc is ready for widespread use. The Synthes training program is “intense on a small scale, allowing surgeons to be thoroughly trained,” he said. “But patient selection and proper surgical training are critical.”

The North American Spine Society recently issued training recommendations for TDR. They include the following:

•The surgeon should have extensive experience in anterior lumbar interbody fusion. The risks inherent in an anterior transperitoneal or retroperitoneal approach-- and, particularly, in a repeat anterior approach—“are significant.”

•The clinical setting should be equipped to deal with potential intra-operative and postoperative complications.

•Surgeons should be accomplished in the possible salvage procedures.

•Surgeons should have performed one to two TDR procedures per month for the preceding 12 months; be proficient with fluoroscopy; be certified in a training course given by the offering technology company; and first undergo a series of mentored operations.

Source: Abstract #113. Delamarter RB, “Lumbar Total Disc Replacement with The ProDisc-L Artificial Disc versus Fusion: A Prospective Randomized Multi-Center Food and Drug Administration IDE Trial”