NEW YORK – Attention, weekend athletes: Don't be too quick to agree to surgery for a common type of knee ligament tear.

A study of Swedish amateur athletes — mostly soccer players — found that those who got an ACL reconstruction right away plus physical therapy fared no better than athletes who started out with rehab and got the surgery later if they still needed it.

Of those in the rehab-first program, fewer than half went on to get the surgery within two years, researchers reported in Thursday's issue of the New England Journal of Medicine.

"It seems that if you start out with rehabilitation only ... you have a good chance of ending up with an equally good outcome as if you had early ACL surgery," said Richard Frobell of Lund University Hospital in Sweden, an author of the work.

"Maybe we will be surprised that a lot of people actually do not need an ACL reconstruction."

Frobell stressed that the study did not include professional athletes. They usually seek surgery to get back into action quickly rather than waiting to see if rehabilitation works.

About 200,000 Americans each year have surgery to replace the anterior cruciate ligament, or ACL, which is crucial for knee stability. It can get torn in sports like football and soccer that require planting the foot and pivoting.

Doctors already knew that not every patient with a torn ACL needs surgery; a middle-aged jogger or cyclist can often get by with a knee brace and rehabilitation, experts say. Frobell said his work suggests that the same strategy might work for athletes who want to return to more strenuous sports like soccer, at least on lower competitive levels.

Some patients with a damaged ACL can cope well at a high level. But doctors can't reliably predict which ACL patients will turn out to be "copers," and Frobell acknowledged his work doesn't help with that.

Doctors and patients currently decide on whether to do the surgery depending on individual factors like just what physical activities the patient plans to pursue and the overall health of the knee, said Dr. Bruce Levy, a Mayo Clinic surgeon.

The operation is an outpatient procedure that involves replacing the ACL with tissue from the patient or a cadaver. Risks include infection and stiffness that may require more surgery. The surgery costs $10,000 or more, depending on whether cadaver tissue is needed.

The new study focused on 121 Swedish amateur athletes, ages 18 to 35, mostly soccer players with some volleyball players. They had new, complete ACL ruptures. Half were randomly assigned to get surgery right away plus physical therapy, and the other half to start with the rehab to improve the knee. The rehabilitation required about 60 sessions on average, two or three times a week, Frobell said. That works out to about five to seven months.

Two years later, both groups reported about the same amount of improvement in ratings for things like pain, performance in sports and how much their knee interfered with their lives. And about 40 percent of each group had returned to their previous level of sports intensity, as measured by that activity's stress on the knee.

Among those treated with physical therapy first, those who eventually got the surgery turned out no better than those who didn't.

Levy urged "a little bit of caution" in interpreting the study.

For one thing, he said, the patients were followed for only two years, so "we really don't know long-term the benefits or consequences of each of the two strategies they tested."

Some 40 percent of the group that began with rehabilitation went on to have the surgery within the two years, and more will probably do so after that, he said.

What's more, the rehabilitation group showed more signs of trouble with the meniscus, a rubbery, cushioning disc in the knee, noted surgeon Dr. Kurt Spindler of Vanderbilt University. That could raise their risk of eventually getting osteoarthritis, he said.

Frobell said researchers will also study five-year outcomes, and look for early signs of arthritis with X-rays and other medical imaging.

The work was financed by government grants and private foundations.