I have an ACL tear that we are going to try and rehab and avoid surgery. I’m scheduled to see a physical therapist for “strength training and perturbation activities.” I get the strength part. What’s perturbation?

Perturbation activities is another way of saying balance training but specifically activities that challenge your balance (not just build up your ability to balance). For example, you may be given ways to practice standing or walking on unstable or uneven surfaces. Once you can do that without losing your balance, the program advances to more difficult tasks. You may be pushed off balance in various other ways.

In other words, your balance, alignment, and stability will be “perturbed” (disturbed) in one way or another. Studies show that when it comes to restoring normal stability and motor movement (called kinetics) of the knee, focusing on both strength training and perturbation yield much better results than just working on improving strength.

Using this type of rehab program for anterior cruciate ligament (ACL) tears helps retrain the muscles (reducing cocontraction) and restores more normal knee motion. Research has shown that patients with ligamentous laxity from damage caused by traumatic (often sports) injuries use a physiologic coping mechanism called cocontraction.

This is the simultaneous contraction of the muscles on both sides of a joint. In the case of the knee, that would be contraction of the hamstrings and quadriceps muscles at the same time. The overall effect of cocontraction is to increase stiffness of a joint that is too lax (or loose).

But does this training eliminate the need for surgery? The answer to this question remains unclear and points to the need for further study of this problem. Several groups around the world have started studying ACL injuries with this intent and focus. Their preliminary results show that as many as two-thirds of athletes with ACL injuries can obtain good knee function and return to sports with the rehab program just described. But the recovery period takes time and some athletes may still opt for surgery in hopes of a faster return-to-play.

In other words, there’s enough evidence to support a nonsurgical approach to ACL tears — even for athletes who intend to return to full sports participation. Combining strength training with perturbation is a key factor in getting good results with or without surgery.