What is the Medial Collateral Ligament (MCL)?
The MCL stands for medial collateral ligament. It is also called as the tibial collateral ligament. A ligament is a strong and flexible band of connective tissue that connects one bone to another bone.
MCL is one of the four major ligaments of the knee joint that connects your thigh bone (femur) to your shinbone (tibia). It provides valgus stability (prevents valgus forces) to the knee joint.
Where is MCL located (MCL Location)?
The medial collateral ligament is located on the inner (medial) side of the knee, but it lies outside the knee joint itself. The MCL runs from the femur’s medial epicondyle to the posterior medial surface of the proximal tibia.
Medial Collateral ligament Anatomy-
MCL originates from the femur’s medial epicondyle and inserts into the posterior medial surface of the proximal tibia. The medial collateral ligament is composed of two portions superficial MCL and deep MCL. Let’s talk about their attachment points (origin and insertion).
Superficial MCL (sMCL)
The superior MCL has two attachments proximal and distal.
It originates from the medial epicondyle of the femur.
After arising from the medial epicondyle of the femur, it travels inferiorly. It inserts on the posterior medial surface of the proximal tibia i.e., on the metaphyseal region of the tibia, about 5 cm distal (below) to the joint line, lying beneath the pes anserinus bursa.
The posterior aspect of the tibial portion of the superficial medial collateral ligament blends with the distal tibial expansion of the semimembranosus tendon.
DEEP MCL (dMCL)
The deep medial collateral ligament is divided into two ligaments: meniscofemoral ligament and meniscotibial ligament
It originates from the femur distal to the superior medial collateral ligament, and It attaches to the medial meniscus.
It originates from the medial meniscus and attaches to the inferior edge of the medial tibial plateau’s articular cartilage.
However, the deep medial collateral ligament is associated with the medial meniscus through the coronary ligament. Despite this association of the dMCL with the medial meniscus, there isn’t any effect on the medial meniscus’ stability.
Biomechanical functions of the medial collateral ligament
Functions of Superficial Medial Collateral Ligament (sMCL)
The sMCL, especially the proximal partition, resists valgus (abduction) forces through all degrees of knee flexion and knee extension. The distal partition of the sMCL resists lateral (external) rotation forces at the knee joint.
At full knee extension, the knee joint is much better able to resist the valgus force than the position of knee flexion. In knee extension, the medial collateral ligament becomes taught, but as the joint flexion increases, the MCL becomes laxer (loose), and a larger joint space opening is available.
Good and colleagues resolved that.
At near to full extension – MCL contributes 57% of the support against valgus forces.
At 25° of knee flexion – MCL contributes to 78% of the support against the valgus forces.
Why between 20 to 30 degrees of knee flexion MCL provides maximum support against the valgus forces?
It is because when the knee is in full extension knee has the support of other structures (support of joint capsule, ACL, meniscus, etc.), so the MCL need not to work for its maximum.
But when the knee goes into flexion, especially between 20 to 30 degrees, other structures go out of the picture, as they have their own role to play, only MCL is left to prevent these valgus forces.
Most injuries to the medial collateral ligament result from the blow to the lateral aspect of the knee. As when the valgus stress exceeds the MCL’s strength, it can lead to a partial or complete tear of the medial collateral ligament.
The MCL also acts as a secondary restraint to the anterior tibial translation (restricting anterior tibial translation) of the tibia on the femur in the nonappearance of the primary restraints against the anterior tibial translation.
Usually, the primary restraint of the anterior translation of the tibia is the Anterior cruciate ligament (ACL). But when you have injured your ACL (ACL not working), The MCL act as a secondary restraint to the anterior tibial translation of the tibia on the femur.
So if you have injured your ACL and if you are rehabilitating that patient, perform the rehabilitation in such a way that you do not stress your MCL (avoid an excessive amount of valgus force) because, in the absence of ACL, MCL is working in restricting the anterior translation of the tibia.
Suppose you have torn your MCL either partial or complete tear. In that case, the load or forces on the anterior cruciate ligament and other ligaments will significantly increase as those ligaments will have to work by themselves. Therefore, the stress on those ligaments will increase, especially the ACL.
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