Cook decided to try SIS on meniscus tissue, which is easier to grow. With a $6,000 grant from MU, he operated on an arthritic dog to create a meniscus defect. Then he put an SIS graft in the joint to see what would happen. The meniscus grew back, leaving the dog with less arthritis.

"Mechanically, it produces a scaffold for new cells to come in and populate it and grow in the right shape," Cook says. "The other thing it does is once you get cells in there, it stimulates those cells to reproduce. It says, 'Hey guys, go to town.' "

In 1997, DePuy contracted with Cook to conduct its SIS research on meniscus regeneration. So far, he has grafted SIS into the knees of about 200 research dogs, using pillow-shaped pieces of the material, each about three-quarters of an inch long and a half inch wide.

After operating on the dogs, he put them in slings for three weeks and then casts for another three weeks, to give the meniscus tissue time to regenerate. "After that, for another six months, it gets tougher and tougher and more functional, like a real meniscus," Cook says. He hopes there will be a similar recovery period for people given an SIS meniscus graft -- about three weeks on crutches, three more on knee braces, then about six months of restricted activity.

"Hopefully, it will be a permanent fix," Cook says. But realistically, he anticipates that the newly grown meniscus may give patients about 10 to 20 years of pain-free function before additional surgery may be needed.

Cook isn't concerned about such safety issues as disease transmission or tissue rejection of pig tissue in humans. Porcine parts, such as heart valves, have been used successfully in people for years.

The SIS that DePuy provides comes from three herds of Specific Pathogen-Free pigs that are checked frequently for viruses and other potential hazards. And several procedures, such as irradiation, are used during processing to make sure the material is sterile. So far, SIS has been used in about 30,000 people with no reports of rejection. "It always goes down the pathway to accommodation in people," Cook says.

DePuy submitted its application last spring to the FDA for human trials of SIS meniscus grafts. Doctors already have practiced the procedure on cadavers and will be ready to start immediately when the FDA gives the go-ahead.