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Lateral meniscus

The lateral meniscus is a C-shaped fibrocartilaginous structure located in the lateral compartment of the knee joint. Compared to the medial meniscus, it is smaller, thicker, and more mobile. Its primary functions are to improve joint congruence, absorb shock, distribute load across the articular surfaces, and contribute to knee stability. The lateral meniscus is clinically important due to its involvement in meniscal tears, sports injuries, and degenerative joint disease.

Synonyms

  • External meniscus

  • Fibrocartilaginous lateral meniscus

  • Lateral semilunar cartilage

Origin, Course, and Insertions

  • Origin / Anterior horn:

    • Arises from the intercondylar eminence of the tibia, anterior to the lateral tibial spine

    • Close to the attachment of the anterior cruciate ligament (ACL)

  • Course:

    • Extends posteriorly in a C-shaped curve around the lateral tibial plateau

    • Covers a larger portion of the tibial surface than the medial meniscus (nearly 80%)

  • Posterior horn / Insertion:

    • Inserts on the posterior intercondylar area of the tibia, anterior to the posterior cruciate ligament (PCL) attachment

    • Connected to the femur via the meniscofemoral ligaments (ligament of Humphrey and ligament of Wrisberg)

Relations

  • Superiorly: Articulates with the lateral femoral condyle

  • Inferiorly: Rests on the lateral tibial plateau

  • Medially: Related to cruciate ligaments (ACL anteriorly, PCL posteriorly)

  • Laterally: Related to the joint capsule and popliteus tendon (which passes through a hiatus in the capsule, separating meniscus from LCL)

  • Anteriorly: Close relation with ACL attachment

  • Posteriorly: Associated with the popliteus tendon and posterior meniscofemoral ligaments

Function

  • Increases congruence between femur and tibia, improving joint stability

  • Absorbs and distributes compressive forces across the knee joint

  • Provides lubrication and nutrition to articular cartilage

  • Contributes to proprioception and joint mechanics

  • Protects against excessive anterior translation of the femur on tibia

Clinical Significance

  • Meniscal tears: Common in sports and trauma, especially due to twisting injuries

  • Bucket-handle tear: More frequent in the lateral meniscus than medial due to mobility

  • Degeneration: Seen with osteoarthritis

  • Discoid lateral meniscus: A congenital variant prone to tears and mechanical symptoms

  • Surgical relevance: Important in arthroscopy and meniscal repair/meniscectomy

MRI Appearance

T1-weighted images:

  • Meniscus appears as uniform low signal intensity (dark)

  • Surrounding fat provides bright contrast, highlighting margins

T2-weighted images:

  • Normal meniscus remains low signal intensity

  • Tears appear as linear or complex areas of high signal extending to the articular surface

STIR (Short Tau Inversion Recovery):

  • Meniscus remains dark in normal state

  • Edema or degeneration in meniscus shows bright signal within or around meniscus

Proton Density Fat-Saturated (PD FS):

  • Normal meniscus: low signal

  • Tears: hyperintense signal extending to articular surface

  • Excellent for subtle tear detection

T1 Fat-Sat Post-Contrast:

  • Normal meniscus: no enhancement

  • Pathologic meniscus (post-surgery, infection, inflammation): may show enhancement around tears or scar tissue

MRI Arthrogram Appearance

  • Contrast fills joint space and outlines the meniscus

  • Tears appear as contrast tracking into meniscus substance or extending through to articular surface

  • Provides improved sensitivity for detecting subtle or postoperative tears

CT Appearance

Non-Contrast CT:

  • Meniscus poorly visualized due to similar attenuation to cartilage and ligaments

  • Only indirect assessment possible (joint space narrowing, calcification)

Post-Contrast CT Arthrogram:

  • Meniscus appears as low-attenuation crescentic structure

  • Tears are identified when contrast material enters or outlines abnormal clefts or defects within the meniscus

  • Useful alternative when MRI is contraindicated

MRI image

lateral meniscus axial cross sectional anatomy 3T MRI AI enhanced radiology anatomy image-img-00000-00000

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lateral meniscus coronal cross sectional anatomy 3T MRI AI enhanced radiology anatomy image-img-00000-00000

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lateral meniscus sagittal cross sectional anatomy 3T MRI AI enhanced radiology anatomy image-img-00000-00000

CT image

lateral meniscus ct sag image

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lateral meniscus ct axial image

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lateral meniscus ct coronal image