Muscle Tissue May Be New Bone Source : Science: Researchers report success in grafting the legs of rats and foresee a technique that would replace the use of artificial joints and metallic implants.

For the first time, scientists have been able to convert muscle tissue into bones of a precise shape, potentially providing an important new source of bone for grafts and wound repairs.

Researchers from Washington University in St. Louis and the National Institutes of Health combined muscle tissue from the legs of rats with finely ground bone powder, added a synthetically produced growth factor and injected the mixture into a rubber mold. Within 10 days after the mold was implanted into rats, the mixture had turned into solid bone in the shape of portions of leg bones, they report today in the Journal of the American Medical Assn.

“There is no doubt in my mind that in the near future this technique will be used for all bone grafts in humans,” said plastic surgeon Roger K. Khouri, one of the paper’s authors. “In the longer term, it will replace artificial joints and metallic implants. Humans will be able to grow their own spare parts.”

“This is starting us thinking about reconstructing and repairing (bone) tissue in a totally new direction,” said UCLA plastic surgeon William Shaw.

At least 200,000 people in the United States receive bone grafts each year. Many undergo the grafts to replace bone surgically removed during cancer treatment; in other cases grafts are used to repair bones badly damaged in accidents or to rebuild congenitally malformed bones.

As many as 250,000 Americans each year undergo hip and knee replacements, primarily because of damage caused by arthritis.

Research pioneered by Marshall Urist of UCLA has led to the isolation of a dozen factors that promote the growth of new bone in humans. Several biotechnology companies are already investigating ways to use them for repair and regeneration of damaged bones. Typically, the growth factors are injected into the site of a wound in the hopes of stimulating surrounding tissue to convert into bone.

But this approach suffers from two major problems, Khouri said. Often, surrounding tissue is injured at the same time bone is damaged, so there is little tissue available to be converted into bone. Also, such injections can cause indiscriminate conversion of muscle into bone, causing loss of function in the area and producing bones of ill-defined shape.

The new approach circumvents both problems by using healthy muscle tissue obtained from elsewhere in the body and by molding it into a precise shape.

In their studies, Khouri, plastic surgeon Basem Koudsi of Washington University and biologist Hari Reddi of the National Institutes of Health removed muscle tissue from the legs of rats, mixed it with bone powder and a growth factor called osteogenin and injected it into molds in the shapes of various bones. The molds were then implanted into the same rats from which the muscle was obtained.

They have since used the technique, Khouri said, to repair rat leg bones with missing segments and to heal skull defects.

Khouri said he hopes to begin tests within humans in a year or two--”once we’re sure it’s safe and it works.”