Lateral Collateral Ligament (LCL): Anatomy, Origin, Insertion, Relations, Function, Clinical Significance, MRI & CT Imaging

Topic

Lateral collateral ligament

The lateral collateral ligament (LCL), also called the fibular collateral ligament, is a strong, cord-like ligament located on the lateral side of the knee. It extends from the femur to the fibula and is one of the four major stabilizing ligaments of the knee joint. Unlike the medial collateral ligament (MCL), the LCL does not attach to the joint capsule or the meniscus, making it a distinct extra-articular stabilizer.

The LCL is vital for resisting varus stress at the knee and stabilizing against excessive lateral opening. It is often injured in sports and trauma involving direct blows to the medial knee or varus force.

Synonyms

Fibular collateral ligament
Lateral knee ligament

Origin and Insertion

Origin: Lateral epicondyle of the femur, just above the popliteus groove
Course: Runs downward and posteriorly as a rounded, cord-like structure
Insertion: Head of the fibula, blending with the biceps femoris tendon

Relations

Anteriorly: Tendon of the biceps femoris (crossing superficially near insertion)
Posteriorly: Popliteus muscle and tendon, arcuate ligament complex
Medially: Lateral meniscus and joint capsule (but LCL remains extracapsular)
Laterally: Subcutaneous tissue and skin of lateral knee
Superiorly: Iliotibial band crosses above the LCL
Inferiorly: Fibular head and peroneal nerve (closely related laterally and posteriorly)

Nerve Supply

Supplied by branches of the common peroneal nerve and lateral articular branches of the femoral nerve

Arterial Supply

Lateral inferior genicular artery
Recurrent branches of the anterior tibial artery
Superior lateral genicular artery

Venous Drainage

Drains into the lateral genicular veins → popliteal vein

Function

Provides primary restraint to varus stress at the knee
Contributes to stabilization against external rotation of the tibia
Works synergistically with posterolateral corner structures to stabilize the knee
Prevents excessive lateral opening of the joint during weight bearing and movement

Clinical Significance

Injury: Commonly injured in varus stress trauma or contact sports
Isolated tears are rare; often injured with posterolateral corner or cruciate ligament injuries
Chronic LCL laxity: Leads to instability and secondary degenerative changes
Surgical relevance: Important to identify in knee reconstruction or repair procedures

MRI Appearance

T1-weighted images:

LCL appears as a low-signal linear band from femur to fibula
Surrounded by bright subcutaneous and intermuscular fat

T2-weighted images:

Normal LCL: dark low signal
Partial tear or sprain: focal thickening or irregular signal with areas of mild hyperintensity
Complete tear: discontinuity with surrounding bright signal (fluid/edema)

STIR (Short Tau Inversion Recovery):

Normal LCL: dark low signal
Injury: hyperintense signal adjacent to or within ligament due to edema/hemorrhage

Proton Density Fat-Saturated (PD FS):

Normal LCL: low signal intensity
Partial or complete tears: hyperintense foci or discontinuity surrounded by fluid signal

T1 Fat-Sat Post-Contrast:

Normal LCL: minimal to no enhancement
Injured/inflamed ligament: contrast enhancement along torn fibers or surrounding tissues

CT Appearance

Non-Contrast CT:

LCL not well visualized; appears as a faint soft-tissue band if resolution is high
Calcification or avulsion fractures at femoral or fibular attachment may be seen

Post-Contrast CT:

Ligament itself does not enhance significantly
Adjacent soft tissue enhancement may indicate inflammation or hematoma
CT arthrography may show joint capsule integrity but LCL itself is best evaluated with MRI

MRI images