Dr. Harner describes the most common cause of a medial collateral ligament (MCL) tear.
Okay, the way the MCL is torn, because it is on the inside of the knee, the knee acts like a hinge joint--it goes straight up and down. If the knee is pushed from the outside, it collapses in, then the MCL is under high forces, and if it gets very high, it starts to tear. And it comes in three grades of tear--a partial tear, a grade 1. A grade 2 is almost a complete tear, and a grade 3 is a complete tear.
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