The bulge on the side of Peggy Hudson’s belly was the size of a cantaloupe. And it was growing.

“I was afraid it would burst,” said Ms. Hudson, 74, a retired airport baggage screener in Ocala, Fla.

The painful protrusion was the result of a surgery gone wrong, according to medical records from two doctors she later saw. Using a four-armed robot, a surgeon in 2021 had tried to repair a small hole in the wall of her abdomen, known as a hernia. Rather than closing the hole, the procedure left Ms. Hudson with what is called a “Mickey Mouse hernia,” in which intestines spill out on both sides of the torso like the cartoon character’s ears.

One of the doctors she saw later, a leading hernia expert at the Cleveland Clinic, doubted that Ms. Hudson had even needed the surgery. The operation, known as a component separation, is recommended only for large or complex hernias that are tough to close. Ms. Hudson’s original tear, which was about two inches, could have been patched with stitches and mesh, the surgeon believed.

Component separation is a technically difficult and risky procedure. Yet more and more surgeons have embraced it since 2006, when the approach — which had long been used in plastic surgery — was adapted for hernias. Over the next 15 years, the number of times that doctors billed Medicare for a hernia component separation increased more than tenfold, to around 8,000 per year. And that figure is a fraction of the actual number, researchers said, because most hernia patients are too young to be covered by Medicare.

In skilled hands, component separations can successfully close large hernias and alleviate pain. But many surgeons, including some who taught themselves the operation by watching videos on social media, are endangering patients by trying these operations when they aren’t warranted, a New York Times investigation found.

Dr. Michael Rosen, the Cleveland Clinic surgeon who later repaired Ms. Hudson’s hernias, helped develop and popularize the component separation technique, traveling the country to teach other doctors. He now counts that work among his biggest regrets because it encouraged surgeons to try the procedure when it wasn’t appropriate. Half of his operations these days, he said, are attempts to fix those doctors’ mistakes.

“It’s unbelievable,” Dr. Rosen said. “I’m watching reasonably healthy people with a routine problem get a complicated procedure that turns it into a devastating problem.”

Ms. Hudson’s original surgeon, Dr. Edwin Menor, said he learned to perform robotic component separation a few years ago. He said he initially found the procedure challenging and that some of his operations had been “not perfect.”

Dr. Menor said that he now performs component separations a few times a week and that, with additional experience, “you improve eventually.” He said he had a roughly 95 percent success rate. In Ms. Hudson’s case, he said, the use of component separation was warranted based on the complexity of her hernia and her history of prior abdominal surgeries.

Component separation must be practiced dozens of times to master, experts said. But one out of four surgeons said they taught themselves how to perform the operation by watching Facebook and YouTube videos, according to a recent survey — part of a broader pattern of surgeons of all stripes learning new techniques on social media with minimal professional oversight.

Other hernia surgeons, including Dr. Menor, learned component separation at events sponsored by medical device companies. Intuitive, for example, makes a $1.4 million robot known as the da Vinci that is sometimes used for component separations. Intuitive has paid for hundreds of hernia surgeons to attend short courses to learn how to use the machine for the procedure. The company makes money not only from selling the machines but also by charging some hospitals every time they use the robot.

Many surgeons — even some paid by device companies to teach the technique — haven’t learned how to properly carry out component separation with the da Vinci, The Times found. In fact, at times they are teaching one another the wrong techniques.

The robot comes with a built-in camera that makes it easy for doctors to record high-resolution videos of their surgeries. The videos are often shared online, including in a Facebook group of about 13,000 hernia surgeons. Some videos capture surgeons using shoddy practices and making appalling mistakes, surgeons said.

One instructional video, paid for by another major medical device company, showed a surgeon slicing through the wrong part of the muscle with the da Vinci. Experts said the result could have been devastating, turning the abdominal muscles into what one described as “dead meat.”

Peper Long, a spokeswoman for Intuitive, said the company hired “experienced surgeons” to lead its training courses. “The rise in robotic-assisted hernia procedures reflects the clinical benefits that the technology can offer,” she said.

In interviews with The Times, more than a dozen hernia surgeons pointed to another reason for the surging use of component separations: They earn doctors and hospitals more money. Medicare pays at least $2,450 for a component separation, compared with $345 for a simpler hernia repair. Private insurers, which cover a significant portion of hernia surgeries, typically pay two or three times what Medicare does.

Repeat Billings

Fixing the torn muscles of a hernia is like closing a suitcase: It’s usually not too difficult to bring the two sides together and zip it up. But a large hernia, like an overstuffed bag, doesn’t have enough slack to bring the muscles back together.

Around 2006, surgeons adapted a technique from plastic surgery, called component separation, to close large hernias. On each side of the torso, they carefully cut the muscle to create slack, resulting in something like an extra zipper in expandable luggage.

Other hernia surgeons were initially afraid to try it. They would have to make incisions that ran from the sternum down to the pelvic bone and would have to distinguish between three parallel planes of muscle, each just millimeters wide. And while making tiny cuts, they would have to carefully avoid bundles of nerves and blood vessels. Cut a bundle, and the muscle becomes useless.

Despite its difficulty, the procedure took off — and with it, the opportunity for doctors to make more money.

The federal government assigns a value to everything a doctor does, from an annual physical to a complex surgery, in order to determine how much Medicare should pay. These values — known as relative value units, or R.V.U.s — are also used by private health plans, and therefore dictate most doctors’ earnings. Many hospitals require their doctors to ring up a minimum number of R.V.U.s. Some doctors get bonuses if they exceed that goal or have their salaries docked if they fall short.

Component separation has a high value. A traditional hernia repair earns between 6 and 22 R.V.U.s for the surgeon, which for Medicare patients translates to $200 to $750. Tacking on a component separation for both sides of the torso brings in an additional 34.5 R.V.U.s., or about $1,200 more for the surgeon. (Medicare also pays the hospital for each procedure.)

When the R.V.U. system began, in 1992, component separation was part of a billing category that consisted of plastic surgery procedures such as reconstructing a patient’s torso after a traumatic accident. Because the procedure demanded a high level of skill and took so much effort, it was given a high R.V.U.

But since 2006, its use for hernias has soared, Medicare data shows.

Part of the rise reflects the fact that some people with small hernias, who don’t need complicated surgery, are nonetheless getting component separations. A study by Dr. Dana Telem, a hernia surgeon at the University of Michigan, found that was happening in about one-third of cases.

Another factor is that some surgeons have been billing insurers up to four times for a single procedure. In 2017, the American College of Surgeons warned them to stop, saying they could bill twice, at most — once for each side of the torso.

Robots on Facebook

As hernia surgeons were dabbling in component separation, a larger shift in surgery was underway: using robots to operate.

Intuitive debuted its da Vinci robot in 2000, with the idea that more precise surgery would shorten recovery times. Surgeons could remotely control the robot’s tiny clamps and scissors, allowing them to carry out complex operations with small incisions.

The company marketed the robot to a variety of specialties, including cardiology and urology. It found notable success in gynecology but faltered in 2013, when an influential study reported that robotic surgery for hysterectomies was no better than a more standard technique.

Around that time, Intuitive made a big push with general surgeons, offering training events around the country where doctors could test out the da Vinci for surgeries like gallbladder removals and simple hernia repairs, one of the most common surgeries in the country.

By 2017, Intuitive brought in more than $3 billion in revenues on the da Vinci, and was trumpeting the largely untapped potential of the hernia market. “We believe hernia repair procedures represent a significant opportunity with the potential to drive growth in future periods,” the company said in its 2017 annual report.

The marketing was “masterful,” said Dr. Guy Voeller, a hernia surgeon in Tennessee and former president of the American Hernia Society. “They made it explode.”

Beyond traditional sales tactics, Intuitive also made inroads into the growing Facebook group, a lively forum where hernia surgeons discussed everything from troubleshooting tricky cases to complaining about their pay.

At first, the group’s members weren’t keen on the robot, questioning whether the flashy new tool was worth its steep price tag. “A lot of added expense with what perceived benefit to the patient?” one surgeon wrote on the Facebook group’s page in 2014.

Around that time, an Intuitive representative placed a phone call to Dr. Eugene Dickens, a general surgeon at a community hospital in Tulsa, Okla.

Dr. Dickens had grown up playing video games and was immediately comfortable at the da Vinci’s remote controls, which he used for dozens of gallbladder, appendix and simple hernia surgeries. Intuitive was paying him to be a consultant. (Since 2013 he has received about $1 million.)

Now the company wanted him to jump into the Facebook fray and win over the naysayers, he said.

“We are getting decimated by this little hernia group,” Dr. Dickens recalled the company representative saying. “Can you join and help defend us?”

He and other robot enthusiasts began to sing the da Vinci’s praises in the Facebook group, he said. (He said that Intuitive did not pay him for his Facebook posts.)

Over time, the group warmed to the robot, not just for simple hernia repairs but also for more complex operations like component separations. Surgeons began posting videos showing off the new procedure, drawing dozens of positive comments.

Surgeons used the da Vinci for more than 1.3 million hernia repairs between 2016 and 2022, Ms. Long said, or about 15 percent of the total procedures by the company’s robots. Only about 13,000 of those hernia repairs were component separations, she said.

Intrigued by the hype, Dr. Dickens taught himself component separation by watching online videos. His first operation went well, he recalled, but a later patient developed a serious complication, necessitating an additional surgery.

Then, at a dinner meeting in Houston, he presented a video of one of his own surgeries to a group of about 50 other doctors, Dr. Dickens recalled. A more experienced surgeon interrupted to say he was operating on the wrong part of the muscle. The embarrassing rebuke felt like a “red flag,” he said, and he stopped doing the procedure, although he is still a proponent of the da Vinci for other operations.

An academic study in 2020 found that “unsafe recommendations often go uncontested” in the Facebook group and warned that “surgeons should be cautious” about using the page for clinical advice.

Dr. Brian Jacob, the hernia surgeon who founded the Facebook group, said that after the study was published, he made an effort to not let bad advice go unchallenged. He said that surgeons have described performing component separations on small hernias. When he sees those posts, he said, he typically comments to say, “That’s not how I would have done it.”

Trashing the Abdominal Wall

In June of 2021, W.L. Gore & Associates, a medical device company that makes surgical mesh used in hernia repairs, posted a video tutorial on its website. It promised to be a step-by-step guide to component separation surgery.

A surgeon narrated as he cut the patient’s abdominal muscles, releasing tissue so he could close a hernia. But he was operating in the wrong place and likely created a new hernia, according to four surgeons who reviewed the video.

“It absolutely trashed the abdominal wall,” said Jeffrey Blatnik, who directs the Washington University Hernia Center. “It was so offensive to the point that we reached out to the company and told them, ‘You guys need to take this down.’”

Jessica Moran, a spokeswoman for W.L. Gore, said that after surgeons flagged the error, the company removed the video; it had been online for 10 months. “We have investigated what happened here to avoid this happening again in the future,” Ms. Moran said.

Dr. Rodolfo Oviedo performed the faulty surgery. Ms. Moran said the company had paid him $4,400 for it.

Dr. Oviedo acknowledged that he had made mistakes but said he had improved. “At some point I was doing it wrong, and nobody’s perfect,” he said in an interview in June, when he was the director of robotic education at Houston Methodist, a major hospital in Texas. He said it was only at some point after the surgery that he learned of his potentially serious errors.

Four months later, Dr. Oviedo offered a new explanation. He said that he had learned of his mistake in real time and had repaired the damage while the patient was still on the operating table. He said the patient, with whom he followed up for 18 months, had not experienced complications. (Dr. Oviedo left Houston Methodist for another job in July.)

W.L. Gore’s video had plenty of company: A study of 50 highly viewed hernia repair videos on YouTube found that 84 percent did not follow all safety guidelines.

In addition to relying on online videos, surgeons also learn new techniques at training sessions paid for by device companies, which typically cover travel and a one- or two-day course. But the companies do little vetting of their instructors, experts said.

Earlier this year, Dr. Blatnik fixed a bad component separation surgery where the original surgeon had cut into the wrong muscle plane. The patient’s intestines were bulging out of her sides, another Mickey Mouse hernia.

Dr. Blatnik said he immediately recognized the name of the surgeon who had operated on the patient because that he had seen that surgeon teach component separation at a course sponsored by a device company. The surgeon has received more than $130,000 in payments over the past decade from companies including Intuitive and Bard, which manufacturers hernia mesh, The Times found.

Looking Pregnant

Academic research is only now starting to quantify the complication rate of component separations for hernias.

In 2019, researchers analyzed five studies of patients who underwent the procedure and found that only 4 percent developed another hernia. But a newer study from the Cleveland Clinic, which followed patients for two years to see if a new bulge had developed, found the number was 26 percent.

Seven years ago, Sandy Aken said, she had a hernia the size of her fist. A surgeon in Huntington Beach, Calif., performed a component separation. Three months later, her belly was still protruding, and she felt like her guts were spilling out. She saw another doctor for help.

“This patient has a significantly compromised abdominal wall with damaged muscle due to the history of component separation,” that doctor wrote in a summary of the visit. Another hernia surgeon told her he could not fix the bulge, she said.

Ms. Aken, 64, now looks nine months pregnant. She cannot bend over without pain, a limitation that forced her to leave her job as a caregiver.

In 2018, Dr. Willie Melvin performed a component separation with the da Vinci on Jennifer Gulledge, whose large hernia made her a good candidate for the operation. But he cut into the wrong part of the muscle, leaving new holes on each side of her body and too little slack to close her original hernia, another surgeon concluded after reviewing her case.

Less than a week later, he performed an emergency surgery to close the original hernia. But the side tears remained.

Dr. Melvin declined to discuss Ms. Gulledge’s case. He said he had a lot of experience with complex hernia cases that other surgeons have referred to him and that he and his partner performed about three component separation surgeries a month. Intuitive paid him more than $25,000 last year to demonstrate his technique to other surgeons and to check the work of doctors who are new to robotic surgery.

In February 2020, Dr. Ajita Prabhu, a Cleveland Clinic hernia surgeon who has studied the frequency of failed component separation, operated on Ms. Gulledge. Dr. Prabhu told her patient that she would try her best, but that the damage from the original surgery was probably irreparable.

She was right. Even with her abdominal muscles sewed back together, Ms. Gulledge lived with intense pain. Routine tasks were difficult: When she changed her granddaughter’s diaper, she had to remind the 2-year-old not to kick “grandma’s bad belly.”

In August, Ms. Gulledge drove 700 miles to Cleveland for a follow-up appointment. She spent four days on the road, sometimes stopping every 30 minutes because it hurt too much to remain behind the wheel.

When Dr. Prabhu examined her, she confirmed Ms. Gulledge’s fear: Another hernia had opened up.

Susan Beachy contributed research and Robert Gebeloff contributed reporting.