the modified muscle and fat implants

Researchers have been able to regrow bone and cartilage by inserting a gene into muscle and fat cells and then implanting them at the site of an injury.

It is hoped the technology could dramatically cut the amount of time patients have to spend in traction after breaking bones and could help improve recovery from cartilage damage such as occurs in knee injuries.

The scientists, based at Harvard Medical School, Boston, found they were able to encourage muscle and fat cells to change into cartilage and then bone by using a form of gene therapy.

Tests in rats showed that the implanted muscle and fat rapidly caused a bridge to form between broken bones within days.

The bones were found to have returned to full strength within 8 weeks of the injury. It can typically take broken bones in humans several months to heal.

Writing in the journal of European Cells and Materials, Professor Chris Evans, from the centre for molecular orthopaedics at Harvard Medical School, said: "Further development of these methods should provide ways to heal bone and cartilage more expeditiously, and at lower cost, that is presently possible.

"Those receiving gene-activated muscle underwent rapid healing, with evidence of bridging as early as 10 days after implantation and restoration of full strength by eight weeks."

Professor Evans and his colleagues are due to present some of their findings at the European Cells and Materials Conference in Davos, Switzerland this week.

The gene therapy technique takes advantage of a defect that is found in patients suffering from an extremely rare disease, known as fibrodysplasia ossificans progressiva, which causes bone to form in the patients' muscles.

These patients carry a variation of a gene that codes for a molecule called bone morphogenetic protein.

The researchers found that they could introduce this defective gene into healthy muscle and fat using a virus that inserts the gene into the cell's DNA. When the muscle or fat is then implanted into the site of a broken bone, it starts to convert to bone.

In rats they found that treated muscle was faster and more effective at healing than fat. The treated fat also improved healing.

Judith Hoyland, a researcher in regenerative medicine who was also involved in the project, said: "We showed that cells implanted into the animal did actually migrate to the injured tissue and were forming bone."

The scientists added that the modified muscle and fat implants not only create new bone, but they also promote the body's own healing process causing it to grow new bone. Pilot tests in rabbits also showed the implants could repair damaged knee cartilage.

The researchers are now conducting further animal trials before attempting the technique in human patients.

Doctors hope that donated muscle or fat could be treated with the virus and implanted into patients with severe injuries or birth defects to help speed up their recovery.

Muscle or fat taken from the patients themselves could even be used to help reduce the risk of rejection.