WASHINGTON -- Using a narrow tube and some specially designed silk, researchers said on Monday they had been able to grow ligaments that should one day offer a grow-your-own knee repair operation.

They said their replacement Anterior Cruciate Ligaments (ACL) could help many of the half-million or so people who tear them every year in the United States alone.

The ACL starts at the center of the knee and connects the leg to the thigh. It stabilizes the knee joint.

Greg Altman, a former offensive tackle on the Tufts University football team, tore his a few years ago and became interested in learning ways to help patients like himself.

He led a team that has figured out a way to grow a new ligament using a patient's own cells. It will have to be tested in animals, but Altman told a meeting of the orthopedic research Socie like a real human ligament.

"Even if this works there is nothing they can do for me," Altman, who is studying for his Phd at Tufts, said in a telephone interview. "I am over the hill."

Currently, a torn ACL is usually replaced with a piece of the hamstring.

Altman's team started with bone marrow stromal cells, which are a kind of progenitor cell found in the bone marrow. They are similar to stem cells in that they can be reprogrammed to produce a variety of different cells.

But the reprogramming is hard to do. Altman's team set up a mechanical system -- the bioreactor -- to imitate the stresses and strains a ligament undergoes to see if that would do the trick.

They seeded the cells onto their specially designed silk matrix and loaded it into a tube.

"We were able to load the growing tissue in torsion and in tension which reflects more appropriately the 'in vivo' (in the body) environment of the ACL," Reuters quoted Altman as saying.

What they got resembled a human ligament. "When we rip them they match the material properties of the ligament," he said.

In a more scientific approach, they looked for the "markers", the special proteins that mark ligament cells.

"We get the cells to elongate into a morphology similar to ligament cells. They produce matrix component, a protein found in ligament." Genetically, the cells looked like natural ACL cells, Altman said.

Altman, who has formed a company called Tissue Regeneration Inc. to develop and market the product, said he hoped to eventually have a process that would allow a patient to walk soon after the ligament is surgically installed. "They'll have a stabilized knee from the get-go," he said.

The idea would be to use a needle to take a patient's own bone marrow cells, grow them in the bioreactor, and then implant the ligament into the patient. Because the cells would be a patient's own, there would be no risk of rejection.