A medial collateral ligament (MCL) injury is damage to the MCL, which is one of the ligaments in the knee joint that helps keep the knee from moving side to side. An MCL injury can be a stretch, partial tear, or complete tear of the ligament. MCL injuries happen when excessive pressure is put on the knee joint, causing a torn ligament. This can occur from getting struck in the knee, bending or twisting the joint too forcefully, or wear and tear of the ligament over time through repeated stress and pressure. MCL injuries are common in athletes playing sports such as football, soccer, and tennis. Symptoms of an MCL injury include pain directly over the ligament and swelling of the torn ligament and/or knee joint. Treatment for MCL tears usually involves using crutches to limit the amount of weight put on the affected knee, and most MCL tears do not require surgery to make a full recovery unless other ligaments such as the anterior cruciate ligament (ACL) are also significantly damaged. Recovery time can vary depending on the severity of the injury, but most teens with a low-grade MCL tear are back to sports within 6 weeks.