This new procedure was performed at University of Pittsburgh School of Medicine using five patients.
They were put through a new stem cell technique using pig bladder tissue.
Scientists implant thin sheets of material, manipulating the patients' stem cells to the injury site.
Through intense physical therapy, the new material and cells are stretched together with the remaining muscle.
"They get these signals. They say, okay I get it, I'm supposed to line up like this, and they recruit their own new blood supply, their own new nerves and they basically start forming new tissue this way. This is a major step forward," said Dr. Steve Badylak of the University of Pittsburgh.
Patients in this study were all treated within six months from the initial injury.
Researchers say that the technique will be more effective for patients treated immediately after their injuries.