Medial Collateral Ligament

Donald H. Johnson MD, FRCS

Key Points

The medial collateral ligament (MCL) is a broad ligament that attaches to the medial femoral epicondyle and to the medial aspect of the tibia under the pes anserinus muscles, 4 cm below the joint line. The anterior fibers of the ligament tighten during knee flexion.
The MCL is the primary restraint against valgus stress, which in turn is the primary cause of injury to the ligament. This stress is common in contact sports such as football, hockey, and wrestling. MCL injury is the most common ligament injury to the knee.
The clinical examination of the MCL involves stressing the knee with a valgus force. The knee should be examined both in 30 degrees of flexion and in full extension.
Most injuries of the MCL are partial isolated injuries and can be treated conservatively.
Operative repair is only considered in Grade 3 MCL injuries. Grade 3 injuries, which are often associated with injuries to the anterior cruciate ligament (ACL) and posterior cruciate ligament (PCL), involve instability both in 30 degrees of flexion and in extension.
When warranted, medial repair is performed after a diagnostic arthroscopy with attention to conservative use of a fluid pump, for fear of fluid extravasation through the ruptured medial capsule.
The reconstructed knee must be protected post-operatively against valgus stress, but range of motion is allowed to prevent stiffness and to stimulate healing of the ligament.

The medial supporting structures of the knee are divided into static and dynamic stabilizers. The pes anserinus muscles (sartorius, gracilis, and semimembranosus muscles) are flexors and internal rotators of the knee, which act as dynamic stabilizers. The semimembranosus is a stabilizer of the posteromedial corner, having insertions, which provide capsular reinforcement along tibial and popliteal insertion. In addition, the vastus medialis obliquitous attaches to the adductor tubercle and is associated with the tibial attachment of the medial collateral ligament (MCL).

The static stabilizer is the capsuloligamentous complex. The MCL is a broad ligament (10 to 12 cm in length) that attaches to the medial femoral epicondyle and to the medial aspect of the tibia under the pes anserinus muscles, 4 cm below the joint line. The anterior fibers of the ligament tighten during knee flexion. The capsular tissue is reinforced by the vastus medialis anteriorly. In its middle third, the capsule consists of meniscofemoral, meniscocapsular, and meniscotibial portions that lie under the deep MCL. Hughston and Eilers (1) have described the posterior portion of the capsule as the posterior oblique ligament (POL). This complex, which is tense in extension and loose in flexion, forms a sling around the posterior aspect of the medial femoral condyle and becomes confluent with the posterior capsule of the knee.

The MCL is the primary restraint against valgus stress. At 25 degrees of knee flexion this structure provides 78% of the restraining force against valgus injury. With extension, it provides a decreasing role, providing 57% of the restraining force at five degrees. In knee extension, the anterior cruciate ligament (ACL) and the posteromedial corner (POL, medial meniscus, and the semimembranosus) increase their
contribution to valgus restraint. Some authors have suggested that the ACL is much more significant in providing valgus restraint (2).

Hughston (1) suggested that the MCL and ACL act synergistically. When the tibia is displaced anteriorly, the ACL becomes taut and restricts additional anterior displacement; however, the femur’s posterior translation is also impeded by the conformity of the medial meniscus and its attachment to the POL. Similarly, both the ACL and medial capsuloligamentous complex check valgus instability.

The healing process of the MCL has been thoroughly examined by Frank et al. (2a). The process contains an inflammation phase (72 hours), a repair and regeneration phase (six weeks), and a remodelling phase (approximately one year). Forty weeks after trans-section in rabbit medial collateral ligaments, the repair tissue was shown to be composed of Type III collagen scar tissue, and it was found to be more lax and mechanically inferior to a native ligament in a sham operation group. The maximum tensile strength regained is approximately 70%. Canine studies can be found to support the concept of increased MCL strength with surgical repair, and for improved strength and results with early range of motion and nonoperative treatment.

Mechanism of Injury

The MCL is injured primarily by a valgus stress to the knee. This is a common mechanism of stress in many contact sports such as football, hockey, and wrestling; therefore, the MCL injury is one of the most common ligament injury seen in the knee.

Clinical Evaluation: History and Physical Exam

The patient gives a history of a blow to the outside of the knee, followed by pain, swelling, and limitation of motion.

The clinical examination of the MCL involves stressing the knee with a valgus force. The knee should be examined both in 30 degrees of flexion and full extension. The degree of injury can be divided into three groups. The first degree injury presents with local tenderness, pain on valgus stress, but minimal detectable laxity of less than 5 mm. Grade 2 injuries have local tenderness, pain on valgus stress, and 5 to 10 mm of laxity with an end point. Grade 3 injuries have 10 mm of laxity, and no end point on valgus stress in full extension. The Grade 3 injury usually is associated with an injury to either the ACL or posterior cruciate ligament (PCL).

Imaging

Plain x-rays are usually required to rule out an associated lateral tibial plateau fracture. Stress radiography using the Telos (Austin Associates, Fallston MD) device can quantify and compare the laxity to the opposite normal knee. MRI evaluation can determine the site and degree of injury to the ligament, as well as evaluate other associated injuries (3).

Treatment

Most injuries to the MCL are partial isolated injuries, and can be treated conservatively. The early literature suggested that MCL injuries should be treated operatively (4); however, Indelicato (5) advocated conservative treatment for all tears of the MCL. Similarly, a concept to repair only the MCL and leave the cruciate ligament injury in the recreational athlete has fallen out of favor. It is important to diagnose any associated injuries to the cruciate ligaments because early surgical intervention may necessary.

The conservative care of the isolated MCL injury should be protection against valgus stress using a brace that allows motion of the knee, but protects against a valgus stress. Prolonged immobilization, such as a long leg cast, has been shown to have a deleterious effect on the healing of the medial ligament (2).

Treatment of the Combined Medial Collateral Ligament Injury

In distinction from the isolated ACL injury, there is less information published on the treatment of combined ligament injuries in the MCL and ACL or PCL.

Operative repair is only considered in the Grade 3 MCL injury that is unstable both in 30 degrees of flexion and in extension. Shelbourne and Carr (6) has advocated conservative treatment of the MCL for the combined injuries. They feel that the MCL and the PCL have potential to heal, as long as they are protected. They also suggest that the MCL should be allowed to heal, and a late reconstruction done for the cruciates only if necessary. This approach avoids the stiffness that may be associated with doing an open MCL repair combined with a anterior cruciate ligament reconstruction. The patient would rather have a knee with some residual laxity compared to a stiff painful knee that may result from overly aggressive surgery.

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