The human knee has four major ligaments that contribute to its stability. The collateral ligaments are the ones on the left and right sides of each of your knees. The lateral collateral ligament (LCL) can be found on the outside of the knee. It connects your femur (thigh bone) to your fibula (the smaller bone in the lower leg). The medial collateral ligament (MCL) can be found on the inside of the knee. It connects the femur to the tibia (the larger bone in the lower leg).
The cruciate ligaments (ACL and PCL) that are found inside the knee joint are much better known because they are injured more frequently than the collateral ligaments. However, injuries to the collateral ligaments are still quite serious and should be treated by your physician. LCL injuries and MCL injuries are typically caused by blunt trauma to the knee that pushes it sideways. This is especially common during contact sports such as football and soccer.
If you experience pain and swelling in your knee, especially after physical activity, contact your doctor to check for ligament injuries and proper diagnosis.