After 12 months, the average improvement among people who received real surgery and those who got sham surgery was essentially the same. (BIGSTOCK)

One of the most common types of knee surgery performed in the United States is no more effective than fake surgery, at least for the first year, according to a new study.

The new evidence should give doctors pause before they try to repair the meniscus, which cushions the bones of the knee, according to the Finnish doctors behind the research published in the New England Journal of Medicine.

The experiment involved 146 volunteers whose knee pain appeared to be caused by wear and tear of that cushion. None of the participants had a recognized injury or osteoarthritis, both situations for which the surgery is already known to be ineffective.

After 12 months, the average improvement among the people who received real surgery and those who got sham surgery was essentially the same, said the research team, led by Teppo Jarvinen of University of Helsinki.

There was no significant improvement in knee pain after exercise and no sizable improvement in the likelihood that a patient would require subsequent knee surgery.

But Craig Bennett, chief of sports medicine at the University of Maryland Medical Center, cautioned that the findings should not be over-generalized. One problem, he said in a telephone interview, is that sham surgery is, in fact, a surgical procedure with potential benefit.

People with knee pain who seem to be candidates for meniscal repair may be suffering because of debris in a swollen knee joint. “If you scope the knee (without touching the cushion), that will often help even if you don’t completely address the torn-meniscus issue,” he said.

During an arthroscopic examination, where fluid is injected to give doctors a good view, “you’re taking out the junky, thick, irritating fluid that can give a lot of people their pain,” he said.

During both sham and regular surgery, small holes are poked through either side of the knee, so doctors can insert instruments to examine the joint. With the surgery, known as arthroscopic partial meniscectomy, pieces of the cushioning material that may be out of place and interfering with the motion of the knee are trimmed away.

Because about 700,000 such surgeries are done in the United States each year at a cost of $4 billion, the new findings “will not be welcomed with open arms,” Jarvinen predicted in a phone interview.

The study was done at five medical centers in Finland. All the volunteers had experienced knee pain for at least three months, and doctors believed the problem was a tear of the medial meniscus. Nonsurgical treatment had not helped them.

Patients did not know whether they had real surgery because of the way the researchers set up the experiment. Once a doctor had used arthroscopic techniques to examine the knee and determine that surgery seemed appropriate, the medical team opened an envelope — with their equipment still in place — to reveal whether the patient would receive fake surgery or real surgery.

For sham surgery, the microshaver that is typically used by the surgeon for meniscus removal didn’t have a blade.

The patient was not told which option was randomly chosen, and neither the orthopedic surgeon nor other operating room staff were involved in further care of the patient. On two scales objectively measuring symptoms, there was little difference in outcomes between sham and real surgery. But patients regarded the treatment as a success whether they received real surgery or not. Surveys showed 89 percent in the actual-surgery group and 83 percent in the sham group reported improvement.