WASHINGTON, DC (Feb. 24) - The Porous Coated Motion (PCM) cervical disc, one of several artificial discs currently under development, improves range of motion and may have advantages over multilevel spinal fusion, according to data from a US Food and Drug Administration (FDA) pilot study presented here on Wednesday at the 72nd Annual Meeting of the American Academy of Orthopaedic Surgeons.¹

"This first pilot study shows an advantage with multilevel disc replacement over multilevel fusion," says study author Paul C. McAfee, MD, an orthopedic surgeon at the Scoliosis and Spine Center in Towson, Maryland. According to Dr. McAfee, four such cervical discs are currently being studied, and "2 years from June, the first should be approved."

In the current PCM study 87% of 69 patient participants were able to return to their baseline level of employment within 6 weeks. After 2 years of follow-up, all patients were neurologically normal, and no infections had occurred.

Dr. McAfee also reported new data on another device, the Charité disc,² which has been approved by the FDA for lumbar spine arthroplasty. Although patients who received this device showed an 82.5% increase in their flexion and range of motion 2 years after surgery, he noted that, compared to cervical spine revision, "lumbar disc revision is problematic because we must do the operation from the front," which requires the assistance of a vascular surgeon.

In the cervical disc implant procedure, which lasts approximately 80 minutes, surgeons remove the patient's degenerated disc using an anterior approach, shape the edges of vertebrae, and insert the PCM device. Some patients can have the surgery on an outpatient basis while others may stay in the hospital for up to 3 days; 80% of patients in the present study were discharged within 23 hours. The lower portion of the PCM implant consists of a cobalt-chrome alloy endplate to which a rounded plastic spacer is attached. An upper alloy endplate interfaces with the spacer like a ball and socket, allowing for translatory movement.

Dr. McAfee found that patients implanted with the Charité lumbar disc had a better restoration of disc height than patients who underwent fusions. These patients also reported higher levels of satisfaction with the outcome of their procedure: 82% said they would definitely or probably undergo the artificial disc surgery again compared with 65% of fusion patients. And 64% of patients who received Charité discs said they definitely or probably could exercise again, compared with 53% of the traditional spinal fusion patients.

BMPs and beyond

Along with the implantation of arthroplastic devices, less invasive procedures that make use of osteoinductive growth factors to stimulate spinal fusion are becoming available. Several bone morphogenetic proteins (BMPs) are being studied for their utility in this setting, and are beginning to be applied in spinal fusion procedures. Recombinant human BMP-2, which can be administered laparoscopically, is currently FDA-approved as a bone graft replacement in anterior lumbar spinal fusions, and BMP-7 and BMP-14 are being investigated.

"The dosage must be refined to maximize potential...the dose for anterior lumbar fusion will not be effective in other areas," Jeffrey C. Wang, MD, chief of the orthopedic spine service and associate professor of orthopedic and neurosurgery at the University of California at Los Angeles Comprehensive Spine Center in California, tells CIAOMed. "We need to work out the kinks, but [the use of] these proteins will replace the taking of bone from the pelvis, as is currently done in fusion surgeries."

The future of spinal surgery does not lie in the application of artificial discs, but in the construction of biological discs via gene therapy and osteoinductive stimulants, Dr. Wang observes. Eventually, "gene therapy will replace disc replacement, do it naturally, and stop the degeneration," he adds. "We can inject something very inexpensively and reverse the process, preventing it from accelerating; that is the ultimate goal."

References:

1. McAfee PC, Pimenta L, Crockard HA, et al. Porous coated motion cervical disc replacement: 112 cases performed as an FDA pilot study. Paper presented at: The 72nd Annual Meeting of the American Academy of Orthopaedic Surgeons; February 23-27, 2005; Washington, DC.

2. McAfee PC, Cunningham BW, Blumenthal SL, et al. A prospective randomized FDA study of the Charité Disc replacement. Paper presented at: The 72nd Annual Meeting of the American Academy of Orthopaedic Surgeons; February 23-27, 2005; Washington, DC.