Rabbits Grow Their Own Joint Replacements in Study

Rabbits implanted with artificial bones re-grew their own joints, complete with cartilage, researchers reported on Thursday.

Only a single compound called a growth factor was needed to induce the rabbits' bodies to remodel the joint tissue, said the team at Columbia University in New York, Clemson University in South Carolina and the University of Missouri.

Such a joint should last longer and work more naturally than a metal joint, the researchers said.

Companies involved in making replacement joints and regenerative medicine are expressing interest, said Columbia's Jeremy Mao, who led the study.

"All the tissue was formed by stem cells from the host," Mao said in a telephone interview.

Writing in the Lancet medical journal, the researchers said they set out to make an artificial joint using a biomaterial made out of polycaprolactone and hydroxyapatite. "It is U.S. Food and Drug Administration approved to use the materials for bone regeneration," Mao said.

They replicated a rabbit's leg joint using a laser to calibrate the structure. They infused this porous bone scaffold with a growth factor — a compound that stimulates cells to grow. In this case it was transforming growth factor beta-3.

Ten rabbits fitted with the enriched new joint were hopping around within three to four weeks. Only a few of the 10 rabbits fitted with an unenriched scaffold could move normally, and three rabbits whose joint was surgically damaged and not repaired limped permanently.

"It was a surprise finding," Mao said. They expected it would take more work to get the body to coat the artificial bone with fresh cartilage.

YOUR OWN JOINT

The technique could benefit patients with advanced arthritis. "At this the whole joint really has undergone substantial breakdown," Mao said.

Metal joints only last 10-15 years but this type should last longer, he said. "It's your own joint. It is the joint you made the second time around," he said.

The Arthritis Foundation says 27 million people in the United States alone have osteoarthritis. "As we age, if we live long enough, pretty much half of us will get arthritis," Mao said.

Columbia has a patent on the technology and is speaking to companies about commercial development and human trials, Mao said. "We'd like to speak with FDA," he added.

Many groups are working in the new field of regenerative medicine, which seeks to harness the power of master cells called stem cells to re-grow diseased and damaged tissue.

Some are coating bone scaffolds with stem cells and implanting them but this new method induces the body to do the job itself, saving a great deal of trouble, Mao said.

Dr. Patrick Warnke of Bond University in Australia said not all patients may have this regenerative capacity — especially the elderly.

"For most patients, a standard metal joint replacement is likely to offer a faster and less demanding option than the bioscaffold, with fewer risks associated with immobility," Warnke wrote in a commentary.

Mao's team "have offered a promising insight into what might be on the horizon", Warnke added.

Both the study and commentary are available at http://press.thelancet.com/joint.pdf.

Orthopedic device makers Stryker Corp, Zimmer Holdings Inc and Johnson & Johnson's DePuy unit all make artificial joints.