A common knee surgery for cartilage damage does not benefit patients and may lead to worse outcomes, a 10-year trial suggests.

The study tracked outcomes for patients treated for a meniscus tear, who were given a partial meniscectomy, one of the most common orthopaedic surgeries. Their trajectories were compared with patients who had randomly been assigned to receive “sham surgery”, in which no procedure was carried out.

Patients who had undergone the surgery, which involves trimming frayed meniscus tissue, did not appear to benefit and scored worse on a range of measures designed to measure knee function, pain and progression of symptoms.

Prof Teppo Järvinen, an orthopaedic surgeon and researcher at the University of Helsinki who led the study, said: “Our findings suggest that this may be an example of what is known as a medical reversal, where broadly used therapy proves ineffective or even harmful.”

The meniscus is a C-shaped, rubbery pad of cartilage in the knee joint that acts as a shock absorber between the thigh bone and shin bone. There are two in each knee.

A meniscus tear, in which the edges of the tissue become frayed, can occur due to a sudden twist of the knee while playing sport. Damage can also occur gradually over time and MRI scans often reveal meniscal tears in healthy people with no symptoms.

“We now know that these meniscal tears are very frequently found in patients with no symptoms,” said Järvinen. “Over the past 20 years, evidence has accumulated to suggest that most of these findings on MRI are purely incidental.”

Symptoms linked to a meniscus tear include knee pain, stiffness, difficulty bending the knee or a crunching or clicking feeling when the knee moves.

The study recruited 146 patients, aged 35 to 65, from five Finnish hospitals. About a third had been diagnosed with a meniscus tear after an acute sports-related injury or twisting of the knee, while two-thirds had gradually started to experience symptoms. The patients were randomly assigned to receive either meniscus surgery or sham surgery, in which incisions were made but no operation was carried out.

After 10 years of follow-up, the group who received meniscus surgery had poorer knee function, greater progression of osteoarthritis and a higher likelihood of subsequent knee surgery.

Mark Bowditch, a consultant knee surgeon and former president of the British Orthopaedic Association, said that best practice guidelines had changed in recent years to reflect emerging concerns about the limited benefits of surgery. This included extending the recommended waiting period to see whether symptoms resolved by themselves or with physiotherapy, from three months to six months.

“In the past, three-quarters of patients might have had surgery, but now it’s [closer to a quarter],” he said. “We have an approach of ‘think before you strike’. Surgery should not be the first step.”

However, he said there were subsets of patients who may still benefit, based on his clinical experience. “If you’re operating to treat pain, that is very unpredictable,” he said. “But there’s a group who have a mechanical sensation of something catching – that group has a more predictable benefit.”

Järvinen said many independent, non-orthopaedic organisations providing clinical guidelines have recommended that the procedure be discontinued. “Still, for example, the American Academy of Orthopaedic Surgeons (AAOS) and the British Association for Surgery of the Knee (BASK) have continued to endorse the surgery,” he added. “This effectively illustrates how difficult it is to give up inefficient therapies.”

The findings are published in the New England Journal of Medicine.