DÜSSELDORF, Germany — The medical treatment for Lindsey Berg’s arthritic left knee has not been approved by the Food and Drug Administration, and neither her professional volleyball team in Italy nor the United States Olympic team would help with the cost. But for Berg, a gold medal hopeful, the chance to dull the chronic pain was worth the money, and the risk.


So between the end of her professional season and the start of Olympic practices in California, Berg stopped at the office of Dr. Peter Wehling on the bank of the Rhine River. “I’ve been struggling with knee pain for the last four years and just continuing to play on it,” said Berg, 31, who had tried surgery and cortisone injections to little avail.


After examining her, Wehling and his team drew syringes of her blood. First they incubated it. Then they spun it in a centrifuge. The blood cells produce proteins that reduce inflammation and stimulate cellular growth; sometimes additional anti-inflammatory proteins are added to the solution. Finally, Wehling injected the orange serum into Berg’s knee.


The price came to 6,000 euros, or about $7,400, out of her own pocket, but with the Olympics in London coming up, any treatment that might make her knee better was worth it. “It’s your body and your money because they’re not paying for it,” she said with cheerful resignation, on the fourth day of her treatment.


Wehling’s practice has become almost a pilgrimage site for athletes trying to prolong careers that have tested the limits of their bodies. It has also been the subject of no small amount of speculation after word leaked last year that the Los Angeles Lakers star Kobe Bryant had flown to Düsseldorf for the treatments. Alex Rodriguez of the Yankees traveled there as well. After the N.B.A. season ended, Lakers center Andrew Bynum, Bryant’s teammate, said he, too, would try it.


Commentators wanted to know if there was something fishy that required Bryant to go abroad for medical treatment. As his scoring average increased and the aging star seemed rejuvenated, the interest in the trips to Germany and the unusual treatment grew.


To answer the most common questions: Wehling’s practice is not at the end of a dark alley but in a modern building south of the city’s old town; it is brightly rather than dimly lighted, with orange floors and a water cooler in the waiting room; and Wehling seems more like a true believer in his Regenokine therapy than a snake-oil salesman. He said he was careful not to use any substances banned by athletic governing bodies.


Biologic medicine is a rapidly growing field. Wehling’s Regenokine treatment might sound similar to another blood-spinning treatment, known as platelet-rich plasma, or P.R.P., that has gained popularity in the United States in recent years. In that procedure, the goal is to produce a high concentration of platelet cells, which are believed to speed the healing process. Wehling said his treatment differed from P.R.P. because he heats the blood before it is spun to increase the concentration of anti-inflammatory proteins, rather than the platelets, in his cell-free solution.


The idea is not just to focus on mechanical problems in the joints or lower back but to treat inflammation as a cause of tissue damage as well as a symptom.


“The potential of biology to treat orthopedic problems is high because it has only been developed a little,” Wehling said in an interview.


“It has to be embedded in a good concept more broadly,” he added, emphasizing that sleep, diet and conditioning are among the important components to go with the injections. “There’s no such thing as the one therapy that fixes everything.”


On a recent morning he treated not only Berg but also a basketball player, a golfer, a Hollywood executive and a former martial artist.