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Posterior root of lateral meniscus

The posterior root of the lateral meniscus is the attachment site of the posterior horn of the lateral meniscus to the tibial plateau. It anchors in the posterior intercondylar region of the tibia, located just anterior to the insertion of the posterior cruciate ligament (PCL). This root is essential for stabilizing the lateral meniscus, maintaining hoop stresses, and protecting the articular cartilage.

Compared with the medial meniscus, the lateral posterior root is less frequently torn, but when injured, it can result in meniscal extrusion, altered biomechanics, and rapid progression of lateral compartment osteoarthritis. Posterior root tears of the lateral meniscus are commonly associated with ACL injuries and trauma.

Synonyms

  • Posterior horn root of the lateral meniscus

  • Tibial root of the posterior lateral meniscus

  • Posterior lateral meniscal attachment

Relations

  • Superiorly: Lateral femoral condyle articular cartilage

  • Inferiorly: Posterior intercondylar region of tibia

  • Anteriorly: Anterior cruciate ligament (ACL) and meniscofemoral ligaments (Humphrey and Wrisberg)

  • Posteriorly: Posterior cruciate ligament (PCL)

  • Laterally: Body of the lateral meniscus

  • Medially: Intercondylar notch structures

Function

  • Anchoring: Provides firm tibial fixation for the posterior horn of the lateral meniscus

  • Load transmission: Converts axial loads into circumferential hoop stresses

  • Joint stability: Works with ACL and PCL to stabilize tibiofemoral articulation

  • Shock absorption: Protects cartilage during weight-bearing and pivoting motions

  • Kinematics: Facilitates meniscal motion during flexion, extension, and rotation

Clinical Significance

  • Root tears: Can cause extrusion of the lateral meniscus and rapid progression of osteoarthritis

  • Association: Frequently linked with ACL injuries, PCL injuries, or high-energy trauma

  • Consequence: Loss of root attachment eliminates meniscal function, leading to instability and cartilage degeneration

  • Symptoms: Lateral joint pain, popping, swelling, mechanical catching or giving way

  • Surgical importance: Repair is essential; untreated tears accelerate lateral compartment osteoarthritis

  • Imaging role: MRI is gold standard; CT arthrography valuable when MRI is contraindicated

MRI Appearance

  • T1-weighted images:

    • Normal root: low signal (dark), triangular attachment to tibia

    • Tears/avulsions: intermediate signal clefts or discontinuity at tibial insertion

    • Bone marrow edema adjacent to tibial attachment may appear as intermediate signal

  • T2-weighted images:

    • Normal root: uniformly dark

    • Tears: bright linear or irregular hyperintense defects disrupting root continuity

    • Root avulsions: high-signal gap at insertion, often with meniscal extrusion

  • STIR:

    • Normal: dark

    • Pathology: bright hyperintense signal consistent with edema or avulsion

  • Proton Density Fat-Saturated (PD FS):

    • Normal: compact, dark, well-defined root

    • Tears: bright signal clefts or defects extending to tibial surface

    • Excellent for subtle root detachments and partial tears

  • T1 Fat-Sat Post-Contrast:

    • Normal: minimal to no enhancement

    • Post-repair: scar tissue enhances

    • Persistent non-enhancing gap indicates recurrent tear

MRI Arthrogram Appearance

  • Contrast fills clefts or avulsed root defects

  • Highlights communication between joint fluid and root tear

  • Differentiates true tear (contrast entry) from degeneration (no entry)

  • Particularly helpful in ACL-associated posterior root tears

CT Appearance

Non-Contrast CT:

  • Root not well visualized directly (soft-tissue density)

  • Indirect indicators: joint space narrowing, subchondral sclerosis, osteophytes

  • Chronic avulsion may show bony fragment at insertion

Post-Contrast CT (standard):

  • Root remains indistinct without intra-articular contrast

  • Only perimeniscal/post-surgical changes inferred

CT Arthrogram Appearance

  • Contrast outlines the posterior root attachment

  • Linear contrast-filled clefts or contrast pooling at tibial insertion indicate root tears or avulsion

  • Extravasation of contrast suggests complex or displaced tears

  • Especially useful in patients unable to undergo MRI

  • Superior to conventional CT for meniscal root pathology and cartilage assessment

MRI images

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

MRI images

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

MRI images

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