US researchers say that people who lost large amounts of muscle in wars or accidents were able to regrow it with the help of a pig bladder implant.
The study included five men who had sustained serious injuries to their thighs or lower legs, said the findings in the journal Science Translational Medicine.
"Frankly, most of these patients have been through hell," said researcher Stephen Badylak, professor of surgery at the University of Pittsburgh School of Medicine.
"They've lost anywhere from 50 percent to 90 percent of the mass of a particular muscle group. And with it, serious loss of function of their affected limb."
Two of the participants were military personnel wounded in explosions, two had been in skiing accidents and one had exercise-related muscle injuries.
While the human body can regrow small amounts of muscle, it cannot typically replace large volumes of loss.
But when researchers implanted a scaffold made of pig bladder tissue, known as extracellular matrix, three of the five patients gained 20 percent or more in strength six months after the surgery.
The scaffold worked by recruiting the patient's own stem cells to the site and encouraging them to regrow muscle tissue, researchers said.
The treatment was delivered a long time after the injuries were incurred, ranging from 13 months to seven years.
Researchers hope for even better results if the implant can be made sooner.
The same types of scaffolds are commonly used in repairing abdominal hernias and in breast reconstruction.
"All of the patients reported an improved quality of life," said the study, which was funded by the US Department of Defense.