Dr. Canale, who says he receives no support from the P.R.P. industry, said: “The bottom line is that most think it works. The operative word is ‘think.’ They don’t know if it works. They have a feeling it does.”

Dr. Rodeo, who also reports having no conflicts of interest, said he understood that response. “Unfortunately in our field, there often is acceptance and use before there is data,” he said.

The Next Big Thing?

As orthopedists and other sports medicine doctors argue about this particular treatment, another popular treatment is forming. It leapt to the public and medical world’s attention this year when Bartolo Colon, a pitcher for the New York Yankees, made an astonishing comeback from elbow injuries and a torn rotator cuff that had plagued him for years and had kept him from pitching for all of 2010.

In May, Mr. Colon and his doctor, Joseph R. Purita, an orthopedic surgeon in Boca Raton, Fla., reported that Mr. Colon was treated with P.R.P. and “stem cells” — his own fat and bone marrow cells, injected into his shoulder and elbow. Dr. Purita worked with the Harvest Technologies Corporation, a Massachusetts company that also supplies equipment for P.R.P.

The opening scenes seem familiar to those who followed the saga of P.R.P.

Once again, there is a rationale behind the treatment, said Rocky Tuan, director of the Center for Cellular and Molecular Engineering at the University of Pittsburgh Medical Center.

The reasoning began with questions about why P.R.P. is not clearly effective. The problem may be that growth factors released from platelets need cells that can respond. But most tissues in joints and tendons have very few cells.

“That’s where stem cells come in,” Dr. Tuan said. Fat and bone marrow contain stem cells that might grow into joint or tendon if they were placed in the right environment. And if a patient also gets an injection of P.R.P., a tendon or joint might actually heal.

The key word, of course, is “might.”

For now, Dr. Tuan said, “no systematic study has been done.”