Overview
A medial collateral ligament (MCL) injury is an injury to the ligament on the inner part of the knee. This ligament keeps your shin bone (tibia) in place. It can be a stretch, partial tear, or complete tear of the ligament.
Causes
Pressure or stress on the outside part of the knee (ex. a block to the outside part of the knee during football)
Symptoms
Knee swelling
Locking or catching of the knee with movement
The knee gives way or feels like it is going to give way when it is active or stressed in a certain way
Diagnosis
Physical examination and medical history consultation
X-rays
MRI
Treatment
RICE (Rest, Immobilization, Compression, Elevation)
Non-steroidal anti-inflammatory drugs
Physical therapy
Surgery
Source: http://www.nlm.nih.gov/medlineplus/ency/article/001076.htm