Human muscle can repair itself on its own, so long as it doesn't suffer severe damage. But researchers now say that a new surgical technique can enable the regeneration of some muscle after large amounts are lost in accidents or war injuries, offering a much improved path to recovery. The technique involves implanting a small biological scaffolding at the injury site and then entering patients into an aggressive physical therapy regimen, and researchers say that the initial results have led to quality of life improvements for all patients of the procedure.

"We are very confident in the science behind it."

In a paper published today, five patients are reported to have successfully regrown muscle, with three of the five seeing at least a 25 percent functional improvement to the injured limb. In all cases, the patients had previously lost over half of their treated limb's muscle and were no longer seeing improvements through physical therapy. "The problem of volumetric muscle loss is truly an area with an unmet clinical need," Stephen Badylak, a University of Pittsburgh researcher and corresponding author on the study, says on a call discussing the results.

Areas of large muscle loss usually end up covered in scar tissue, rather than new muscle, limiting how far a patient can recover. Physical therapy and other surgeries can help to improve that, but Badylak calls the current options "truly limited." With their new surgical technique, however, Badylak say that surgeons can get cells to avoid turning into scar tissue — and start turning into muscle again.

The process requires a pairing of surgery and physical therapy. In surgery, existing scar tissue is first removed from the injury site. A thin sheet of biological scaffolding — known as an extracellular matrix, in this case made from a pig's bladder — is then implanted in the area and attached to healthy tissue so that new stem cells can reach it. After surgery, the patients are then entered into an aggressive physical therapy regimen within one to two days.

"The cells get the idea."

As the scaffolding begins to degrade, cells receive a signal to come and attempt to rebuild it. By then placing the area under stress from physical therapy, the cells recognize that they should begin forming into muscle. "The cells get the idea," Badylak says. "They go, 'I get it. I'm supposed to line up this way, bear weight, contract, whatever.'"

The human trials build on earlier tests on rodents, which showed that the procedure could allow them to regrow muscle at severely injured portions of their hind limbs. The human trials provide a limited set of results, but the researchers believe in them. "We recognize that this is a small number of patients that we have started with," Badylak says, "but we are very confident in the science behind it."

The research was led by Brian Sicari and Peter Rubin at the University of Pittsburgh's McGowan Institute for Regenerative Medicine, and its results are being published today in Science Translational Medicine.

All of the patients in the trial had an injured leg, with three of the five receiving their wounds in the military, two of which came from IEDs. It should be no surprise that there's interest in seeing what the new procedure can do to help those with military injuries. A portion of the research's funding — about $3 million over the past four or five years — even came from the Department of Defense.

Researchers hope to avoid poor replication of their study

And critically, Badylak says that the entire process is designed so that it "can be utilized literally anywhere that a good surgery is available." It won't be heading out to the field just yet though. The next step will be for the researchers behind this study to carefully train between three to five other institutions in the process so that they can properly attempt to recreate these results.

Badylak paints this tentative step forward primarily as a precautionary measure to protect the integrity of the research: "Frankly, the reason that we're doing this is because if someone reads this article and some surgeon out in the Great Plains decides that, 'You know, all I have to do is buy this stuff, put it into the site,' and they don't get the good results, we'll spend the next 10 years fighting in the literature back and forth about who's right and who's wrong."

If the method really is this effective, he has a point. But there's good reason that those debates happen and that doctors who are uninvolved with the original researchers will now be able to take a look at and review the methodology, trying it out themselves to determine whether its so-far limited results are repeatable. Regardless of who they come from, it's still going to take many more trials to see what the procedure is really capable of.