Most amateur athletes who tear the ACL, or anterior cruciate ligaments, in their knees say that it starts with a pop, like the snapping of a rubber band.

Pain, swelling and an MRI scan to confirm the diagnosis typically aren't far behind.

Then patients have some decisions to make - whether to have surgery to reconstruct or repair the ligament, one of four that stabilize and support the knee, or whether to try rehabilitation and physical therapy to get back on their feet, first.

Increasingly, doctors have steered patients toward quick surgery for ACL tears, with the hope that a fast repair can prevent some of the long-term consequences of these injuries, which include osteoarthritis and tears of cartilage pads inside the knee called the menisci.

But a new study, published in the July 22 issue of the New England Journal of Medicine has questioned that notion, concluding that many patients who first try a course of physical therapy to get back on their feet after an ACL tear, wind up with the same improvements in pain and function two years down the road as those who had immediate surgery.

The implication of the study is that many young, active adults could delay or avoid surgery altogether by giving physical therapy a try first, and they don't appear to increase their risk of osteoarthritis or further knee injury in doing so.

For the study, researchers from Lund University, in Sweden, followed 121 adults with fresh ACL tears for two years. 

Half of the group had immediate surgery. The other half were funneled to a physical therapy program, but they were given the option to eventually have surgery if they wanted it, or if their knees demonstrated continued instability – collapsing, for example, with quick changes of direction.

The participants ranged in age from 18 to 35, and they were all non-professional athletes.

Of the 62 people in the group who had rehabilitation plus early surgery, all but one had the procedure done. In the delayed surgery group of 59, 23 eventually had the procedure performed after an average of 11.6 months while 36 only did rehabilitation.

Over the course of two years, both groups reported substantial improvement in their injuries, and there were no significant differences in pain or function between the two groups.