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Medial collateral ligament

The medial collateral ligament (MCL), also known as the tibial collateral ligament, is a broad, flat band of connective tissue on the medial side of the knee. It is one of the key static stabilizers of the medial knee, preventing valgus stress and excessive external rotation. The MCL has both superficial and deep components that connect the femur to the tibia and blend with the medial meniscus, giving it strong functional integration with the joint capsule.

MCL injuries are among the most common ligament injuries of the knee, especially in athletes, and are typically caused by valgus stress or twisting injuries.

Synonyms

  • Tibial collateral ligament

  • Medial knee ligament

  • Medial stabilizing ligament

Origin and Insertion

  • Origin: Medial femoral epicondyle, just below the adductor tubercle

  • Course: Runs distally and slightly anteriorly along the medial aspect of the knee

  • Insertion: Medial surface of the proximal tibia, approximately 5–7 cm below the tibial plateau

Relations

  • Superficial MCL: Lies extracapsular, superficial to the joint capsule

  • Deep MCL: Shorter and deeper, attached to the medial meniscus and joint capsule

  • Anteriorly: Tendons of pes anserinus (sartorius, gracilis, semitendinosus) cross the distal MCL

  • Posteriorly: Adductor magnus tendon proximally and posterior oblique ligament of capsule

  • Laterally (deep): Medial meniscus, joint capsule, articular cartilage of femoral condyle and tibial plateau

  • Medially (superficial): Subcutaneous tissue and skin

Nerve Supply

  • Branches of the saphenous nerve (sensory innervation to medial knee capsule)

Arterial Supply

  • Genicular branches of the femoral artery and popliteal artery

  • Medial inferior genicular artery provides key supply

Venous Drainage

  • Companion veins of the genicular arteries drain into the popliteal vein

Function

  • Prevents valgus stress at the knee joint

  • Limits external rotation of the tibia relative to the femur

  • Provides medial joint stability during flexion and extension

  • Supports the medial meniscus through its deep fibers

MRI Appearance

T1-weighted images:

  • MCL appears as a thin, dark (low signal) linear structure

  • Surrounded by bright fat, improving visualization

T2-weighted images:

  • Normal MCL remains low signal

  • Acute injury or tear shows bright hyperintensity within or around the ligament

STIR (Short Tau Inversion Recovery):

  • Normal MCL: uniformly dark

  • Strain, edema, or partial tear: bright hyperintense signal within or adjacent to ligament

Proton Density Fat-Saturated (PD FS):

  • Best for detecting partial tears and subtle injuries

  • Normal MCL: dark band

  • Injury: areas of bright hyperintensity or discontinuity

T1 Fat-Sat Post-Contrast:

  • Normal ligament shows minimal or no enhancement

  • Inflamed or injured ligament may show enhancement at tear sites or in adjacent soft tissue

  • Chronic injuries may show thickening without strong enhancement

CT Appearance

Non-Contrast CT:

  • MCL is not well visualized due to low soft tissue contrast

  • Appears as a thin soft tissue band if carefully examined in fat planes

Post-Contrast CT:

  • Normal ligament does not enhance significantly

  • Surrounding inflammation, hematoma, or tumor infiltration may enhance

  • CT useful for assessing avulsion fractures at ligament origin or insertion rather than soft tissue tear

MRI images

Medial collateral ligament (MCL) axial cross sectional anatomy 3T MRI AI enhanced radiology anatomy image-img-00000-00000

MRI images

Medial collateral ligament (MCL) coronal cross sectional anatomy 3T MRI AI enhanced radiology anatomy image-img-00000-00000

CT image

Medial collateral ligament (MCL) ct coronal image