Researchers have created a biologically based spinal implant they say could someday provide relief for the millions of people suffering lower back and neck pain. Instead of removing damaged spinal discs - a surgery known as a discectomy - and fusing the vertebrate bones to stabilize the spine in patients diagnosed with severe degenerative disc disease, or herniated discs, the artificial discs could be used to replace damaged discs, performing better than current implants that are made from a combination of metal and plastic.
Although discectomies prevent pain, the often limit mobility. Human discs look something like a tire, with the outer part, called the annulus, made of a stiff material, and the inner circle, the nucleus, made of a gel-like substance that gets pressurized and bears weight.
To mimic this structure, engineers at Cornell University in Ithaca and doctors at the Weill Cornell Medical College in New York City engineered artificial discs out of two polymers - collagen, which wraps around the outside, and a hydrogel called alginate in the middle. They seeded the implants with cells that repopulate the structures with new tissue. Compared to artificial implants that degrade over time, the researchers found that the new implants get better as they mature in the body, due to the growth of the cells.
"Our implants have maintained 70 to 80 percent of initial disc height. In fact, the mechanical properties get better with time," says Lawrence Bonassar, Ph.D., associate professor of biomedical engineering and mechanical engineering at Cornell.
A surgical procedure approved by the FDA in 2005 for treating the degeneration of the intervertebral disc involves removing the damaged disc completely and replacing it with an implant made from a combination of metal and plastic, with the aim of mimicking the normal movement of the lumbar and the spine.
"Bone or metal or plastic implants are complicated structures which come with a mechanical risk of the structures moving around, or debris from the metal or plastic particles accumulating in the body from wear and tear," says Roger Härtl, M.D., associate professor of neurosurgery at Weill Cornell Medical College and chief of spinal surgery at New York-Presbyterian Hospital/Weill Cornell Medical Center.
Because the new discs integrate and mature with the vertebrae they would have a huge advantage over traditional implants, says Härtl, who is also the neurosurgeon for the New York Giants. This major surgery would also become less invasive, safer and come with fewer long-term side effects, he adds.
Bonassar and Härtl began collaborating on the project in 2006 and have since moved into the animal testing stages. The project has received a US$325,000 grant from Switzerland's AO Spine foundation and $100,000 in support from NFL charities. The research appears online in the Proceedings of the National Academy of Sciences.
