The medial collateral ligament (MCL) runs along the medial (inner) side of the knee joint. It is longer and wider than the other ligaments of the knee. The MCL is also different because it is continuous with the knee joint capsule, has both deep and superficial portions and is attached to the medial meniscus. Some of the ligament’s fibers are tight in full knee extension (fully straightened knee) and help resist hyperextension, while some of the fibers are tight in full knee flexion (fully bent knee). The MCL works to stabilize the medial side and provide rotational stability
The MCL is the most often sprained ligament in the knee. An MCL sprain is a partial or full tear of the ligament’s fibers. This can be a contact or noncontact injury, occuring when the knee is forced inward with a stress or impact to the outer side of the knee. Injuries are most common in athletes during sport activities when the knee is bent. These injuries are more common in males than females. When a MCL injury occurs with an ACL tear and a medial meniscus tear as well, it is referred to as the “unhappy triad.” An MCL sprain can also occurs with a kneecap dislocation. Fortunately, the MCL has a blood supply and therefore has a high potential for healing without surgery, if injured in isolation.
Pain, stiffness and swelling are common complaints with a MCL injury. However, since the MCL is congruent with the joint capsule, and is not inside the joint, swelling does not always occur. The knee will likely be tender to touch along the medial side, often just below the knee joint where the ligament attaches to the bone of the lower leg. Patients with an MCL injury often walk with their knee slightly bent to reduce the pain. Some patients with a more severe MCL injury also complain of side to side instability.
Sprains are classified as Grade I, II or III, depending on the amount of instability - gapping between the femur (thigh bone) and tibia (shin bone). This can be determined clinically by a doctor, physical therapist, athletic trainer or with a MRI. A Grade I sprain does not have any gapping or instability. A Grade II sprain has gapping on the medial side of the knee, with a defined endpoint to this gapping; possible instability may be noted by the patient. A Grade III sprain is a full tear of the ligament fibers, with no endpoint to the gapping of the medial knee, leading to instability.
Isolated MCL sprains are most often treated conservatively, without the need for surgery. Physical therapy is prescribed to help the patient return to sport as quickly and safely as possible. For grade II and III sprains, the knee is often braced for walking, and sometimes the patient is initially required to be on crutches. Return to sport is expected in about 2 weeks for a grade I sprain, 4 weeks for a grade II sprain, and 6 to 8 weeks for a grade III sprain. However, each patient responds to injuries and rehabilitation differently and may take slightly longer to return their prior level of function. Some patients may also need to wear a brace when they return to sport.
If the MCL is injured along with other structures in the knee, the treatment will follow a different course. If the ACL is also torn, surgery to repair the ACL will often be delayed for 5-7 weeks to allow the MCL to heal initially. In some cases, the MCL may be surgically repaired, or replaced with other tissue. This postoperative treatment will include physical therapy for up to 5 months, or longer if the ACL was reconstructed as well.
Laprade, R and C Wijdicks. The Management of Injuries to the Medial Side of the Knee. Journal of Orthopedic and Sports Physical Therapy, 2012.
Marchant, M, et al. Management of medial-sided knee injuries, part 1: medial collateral ligament. American Journal of Sports Medicine, 2011.
Miyamoto, R, et al. Treatment of medial collateral ligament injuries. Journal of American Academy of Orthopedic Surgery, 2009.
Phisitkul, P, et al. MCL Injuries of the Knee: Current Concepts Review. The Iowa Orthopedic Journal, 2006.