The medial collateral ligament (MCL) is one of four ligaments in the knee that work together to form a hinged joint, giving it stability and strength. Located on the inside of the knee, the MCL connects the top of the shinbone (tibia) to the bottom of the thighbone (femur), and provides stability to the inner knee. The MCL is the most commonly injured of all knee ligaments. A blow to the outside of the knee (and sometimes non-contact stress as well) stretches or tears the structures on the inside of the knee.
Injuries to the MCL, called MCL sprains, are categorized by grade. Grade one is the least severe, and indicates only a stretching of the ligament. Grade two is a partial MCL tear, and grade three is a complete tear, which commonly causes joint instability. Most MCL injuries can be managed conservatively and will heal with rest. The majority of patients sustaining MCL injuries (of varying severity) achieve pre-injury levels of activity without surgery. When on rare occasions a surgeon needs to operate, either because the ligament cannot repair itself, or because the MCL injury occurs with other ligament injuries, the operation must be done openly. The MCL cannot be repaired arthroscopically.
Before surgery, the surgeon uses arthroscopy to make a thorough examination of the extent of the injury. Arthroscopy involves inserting a small, pencil-thin camera through a tiny incision. Afterward the surgeon makes a small incision behind the knee and reattaches the ligament to the bone using large stitches, bone staples, or a metal screw. If the tear is in the middle of the ligament, the surgeon stitches the ligament together. The outlook for recovering from a MCL injury is good, whether surgery is required or not. Sometimes, an MCL tear can cause fractures in the growth plates at the end of the bones in adolescents.