What is the tendon that runs behind your knee on the inside of your knee?

If i'm correct it should be your cruciate ligament.Long story short its just plain old wear and tear.Your knee cap covers the two cruciate ligaments beneath your knee and all that it takes to tear or snap them is for example keeping your foot in the same spot and turning your knee.Just awkward positions can ruin your cruciate.Go to a doctor to get it checked out because if the ligament has snapped you will need wire implanted to replace the ligament and you will probably not be able to do serious running ever again.