My BIL tore his MCL, and I was confused when he didn't need any corrective surgery. It was completely torn.
This led me to do some google-ing on the subject. MCL's heal themselves, often, even when completely torn. In fact, one article was all about an experimental procedure that tries to coax other ligaments (ACL, primarily) into also healing by themselves. The article suggested that MCL's heal on their own because blood is able to surround and stay at both ends of the tear. The experimental procedure had a way of placing and holding blood in a similar way around an ACL.
Pretty neat stuff.