The medial collateral ligament (MCL) is a band of tissue that runs along the inner edge of the knee and helps to connect the shin and thigh bones to keep the knee stable and working properly when you move. An MCL injury can range from a mild sprain or partial tear to a complete grade 3 rupture. MCL injuries are usually caused by getting struck in your knee or by bending or twisting the joint too forcefully, causing the ligament to stretch and tear. They are common injuries for athletes playing sports such as football, soccer, and tennis. Symptoms of an MCL injury include pain along the inside edge of the knee, swelling, and difficulty walking or putting pressure on the leg with the hurt knee. Treatment for MCL injuries usually involves using crutches to limit the amount of weight you put on your affected knee, and most MCL tears do not require surgery to make a full recovery unless other ligaments such as the ACL are also significantly damaged. Recovery time depends on the severity of the injury, but most teens with a low-grade MCL tear are back to sports within 6 weeks.