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Bay Area researchers have developed a new technique to help repair injured knees. It could someday change the way many surgeries are done. 
From bike riding to basketball, it would be hard to find a sport that Marty doesn't like. But the financial manager, who asked us not use his last name, also paid a painful price with his right knee.
"I'd just torn my ACL playing basketball for the second time in that knee. I had a pretty bad experience the first time, I had a patellar tendon graft, very painful, took a long time getting back to being active," he says.
Marty turned to San Francisco surgeon, Kevin Stone, M.D., who says the grafts typically involve harvesting bone and tendon from the front of the knee, to rebuild the ACL.
"In the 21st century, we shouldn't be taking away one part of a person's body to rebuild the other, it's somewhat barbaric and we know from long term data that we actually hurt the patient when we do that," says Stone.
One strategy is to wait for human donor tissue to become available. But in Marty's case, Stone was able to offer an experimental alternative -- an animal ligament, known as Z-Lig.
"So a Z-Lig is a pig bone patellar tendon bone, so a pig graft that we can use to rebuild the anterior cruciate ligament [ACL] in a human," Stone explains. 
But first, Stone's team had to find a way to essentially, "humanize" the tissue to prevent rejection. Researcher Thomas Turek said the solution involved identifying and removing a specific antigen found in animal tissue but not in humans.
"The processing actually removes the cells and lipotropes so the device has no recognition," according to Turek. 
The breakthrough allowed Stone to rebuild Marty's ACL with the pig ligament, as part of a pilot study. He believes the Z-Lig has several advantages including consistent quality.
"Now what we can do is take that exact same graft from a young health pig. So we save the patients all the surgical trauma of having their own tissue being used, and we get to have it from a young healthy animal every time," says Stone.
Trial results were successful enough that the Z-Lig received approval for use in Europe. The team now hopes to organize a similar trial in the U.S. for FDA approval.
For Marty, the best part of his rebuilt knee has been forgetting about it. He said, "I feel confident in my knees. In fact, I don't think about it. I feel I can do all the activities I used to do.

Written and produced by Tim Didion - ABC News Bay Area.