Danette Lake thought surgery would relieve the pain in her knees.

The arthritis pain began as a dull ache in her early 40s, brought on largely by the pressure of unwanted weight. Lake lost 200 pounds through dieting and exercise, but the pain in her knees persisted.

When a doctor said that knee replacement would reduce her arthritis pain by 75 percent, Lake was overjoyed. “I thought the knee replacement was going to be a cure,” said Lake, 52 and living in rural Iowa. “I got all excited, thinking, ‘Finally, the pain is going to end and I will have some quality of life.’ ”

But one year after surgery, she said she’s still suffering. “I’m in constant pain, 24/7,” she said.

Most knee replacements are considered successful, and the procedure is known for being safe and cost-effective. Rates of the surgery doubled from 1999 to 2008, with 3.5 million procedures a year expected by 2030.

But Lake’s ordeal illustrates the surgery’s risks and limitations. Doctors are increasingly concerned that the procedure is overused and that its benefits have been oversold. Research suggests that up to one-third of those who have knees replaced continue to experience chronic pain, while 1 in 5 are dissatisfied with the results. A 2017 study published in the BMJ found that knee replacement had “minimal effects on quality of life,” especially for patients with less severe arthritis.

One-third of patients who undergo knee replacement may not even be appropriate candidates for the procedure, because their arthritis symptoms aren’t severe enough to merit aggressive intervention, according to a 2014 study in Arthritis & Rheumatology.

“We do too many knee replacements,” said Dr. James Rickert, president of the Society for Patient Centered Orthopedics, which advocates for affordable health care. “People will argue about the exact amount. But hardly anyone would argue that we don’t do too many.”

Although Americans are aging and getting heavier, those factors alone don’t explain the explosive growth in knee replacement. The increase may be fueled by a higher rate of injuries among younger patients and doctors’ greater willingness to operate on younger people, such as those in their 50s and early 60s, Rickert said. That shift has occurred because new implants can last longer — perhaps 20 years — before wearing out.

Yet even the newest models don’t last forever. Over time, implants can loosen and detach from the bone, causing pain. Plastic components slowly wear out, creating debris that can cause inflammation. Obese patients can put extra pressure on implants, shortening their life span.

The younger patients are, the more likely they are to “outlive” their knee implants and require a second surgery. Among patients younger than 60, about 35 percent of men need a revision surgery, along with 20 percent of women, said a November article in the Lancet. Such procedures are more difficult to perform and are more likely to cause complications.

Yet hospitals and surgery centers market knee replacements heavily, with ads that show patients running, bicycling, even playing basketball after the procedure, said Dr. Nicholas DiNubile, an orthopedic surgeon specializing in sports medicine. While many people with artificial knees can return to moderate exercise — such as doubles tennis — it’s unrealistic to imagine them playing full-court basketball again, he said.

“Hospitals are all competing with each other,” DiNubile said. Marketing can mislead younger patients into thinking, “ ‘I’ll get a new joint and go back to doing everything I did before,’ ” he said.

To Rickert, “medical advertising is a big part of the problem. Its purpose is to sell patients on the procedures.” Knee replacements, which cost $31,000 on average, are “really crucial to the financial health of hospitals and doctors’ practices,” he said. “The doctor earns a lot more if they do the surgery.”