I was in the doctor’s office for a knee injury. When the doctor tested for joint laxity, there was a popping sound and my knee gave way. The diagnosis is a torn anterior cruciate ligament. Does this test usually have this kind of result?

The normal knee is a very tight structure with very little “give.” Movement of one bone against another is called joint play. Every person has a certain amount of joint play in the knee. Some people have more than others.

Tests for joint laxity (looseness) give the doctor an indication of possible injury. When a ligament is damaged or torn, there is increased joint laxity. Often, when the ACL is torn, there is also damage to the cartilage.

The pop you heard may have been a flap of torn cartilage unfolding. It’s also possible that the torn ligament ruptured completely with the maneuver. It’s actually better to have a partially torn ligament rupture in the doctor’s office than when you step off a curb or on the playing field. It was bound to happen sooner or later. In this way, you have a “controlled injury” that can be managed right away.