Your medial collateral ligament -- or MCL -- is located along the inside of your femur -- thigh bone. Your MCL runs down the side of your knee and connects to your tibia -- shin bone. Your MCL functions to prevent your knee from buckling under stress. A bruise to your MCL can occur as the result of a direct blow to the inside of your knee or as the result of an abnormal twisting or movement of your knee. This may also be referred to a contusion.
Recall an instance of injury. If you bruised your MCL, you will likely be able to recall when your injury occurred. You may remember following, colliding with another athlete or a sudden, twisting of your knee joint.
Take note of the location of your pain. A bruised MCL will cause pain and tenderness along the inside of your knee.
Look for bruising and swelling. A contusion crushes your muscle fibers and connective tissues without causing damage to your skin. Your skin may turn a blue-ish, purple color as the result of blood pooling underneath your skin. Swelling may also occur along the inside of your knee.
Visit with your doctor. MCL bruises are usually nothing serious. However, bruises may be an indicator of a more severe injury. Bone fractures, knee dislocations, sprains and ligament damage can also occur to your knee and MCL. If pain from your MCL bruise persists for more than a few days, visit your doctor for a diagnosis.