Overview
The knee is stabilized by several ligaments, but two of the most commonly injured are the medial collateral ligament (MCL) and anterior cruciate ligament (ACL). Both can be injured during twisting, cutting, awkward landings, or contact injuries, but they behave very differently after they tear. The MCL usually has good healing potential, while a torn ACL generally does not heal reliably on its own.
Medial Collateral Ligament (MCL)
Presentation
MCL tears typically result from a force that pushes the knee inward and causes pain along the inside of the knee. Depending on severity, patients may also notice swelling and a feeling of instability.
Conservative Treatment
Most MCL tears, including complete tears, heal without surgery. Treatment typically includes a hinged knee brace, immediate weight-bearing as tolerated, early motion, and physical therapy. More severe injuries may take up to three months to heal.
Surgical Treatment
Surgery for an isolated MCL tear is uncommon. It is generally reserved for unusual tears that cannot heal appropriately, persistent instability despite treatment, or complex multi-ligament knee injuries.
Anterior Cruciate Ligament (ACL)
Presentation
ACL tears are among the major sports injuries we have all come to recognize and are often season-ending injuries for athletes. They commonly occur during cutting, pivoting, sudden changes in direction, or awkward landings. Patients frequently describe a pop followed by rapid swelling, difficulty bending the knee, and a feeling that the knee cannot be trusted or may give way.
Unlike the MCL, the ACL does not have different grades of tearing in the same practical sense. It is essentially all or none. A complete ACL tear results in loss of an important stabilizer of the knee. ACL injuries are also commonly associated with meniscus tears and may occur together with other ligament injuries, particularly the MCL. These associated injuries need to be evaluated because they may require treatment at the same time.
An ACL-deficient knee often calms down after the initial injury. Pain and swelling may improve and many of the early symptoms can resolve, but the underlying instability does not. Continued instability places the meniscus and articular cartilage at risk for further damage and can contribute to progressive degenerative changes and arthritis.
Conservative Treatment
Nonoperative treatment may be appropriate for carefully selected older or relatively sedentary patients with low activity demands and limited functional goals. Treatment focuses on restoring motion, strength, balance, and knee control through physical therapy. Continued instability leaves the knee at risk for additional meniscus and cartilage damage.
Surgical Treatment
For the majority of patients with a torn ACL, reconstruction is recommended to restore stability for sports, work, and normal activities of daily living and to reduce recurrent giving-way episodes that can cause further damage to the meniscus and articular cartilage. Progressive damage can contribute to arthritis and, in some patients over time, ultimately lead to the need for knee replacement.
A torn ACL will not heal on its own and generally cannot simply be fixed. Instead, it is reconstructed using a tendon graft. The graft may come from the patient's own tissue, called an autograft, or from donor tissue, called an allograft. The details of graft selection, the reconstruction itself, and postoperative recovery are covered on the ACL Reconstruction page.