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Posterior horn of medial meniscus

The posterior horn of the medial meniscus is the thickened posterior portion of the C-shaped medial meniscus in the knee joint. It is broader and more firmly attached than the anterior horn, making it more vulnerable to injury, especially in twisting and weight-bearing activities. It provides essential load distribution, joint stability, and shock absorption within the knee.

Because of its strong attachments and limited mobility compared to the lateral meniscus, the posterior horn of the medial meniscus is the most common site of meniscal tears, particularly in degenerative knee disease and sports injuries.

Synonyms

  • Posterior medial meniscal horn

  • Posterior segment of the medial meniscus

  • Posterior medial meniscus

Relations

  • Superiorly: Femoral condyle (medial femoral condyle articular cartilage)

  • Inferiorly: Tibial plateau (posterior aspect of medial tibial plateau)

  • Anteriorly: Body of the medial meniscus

  • Posteriorly: Posterior capsule of knee joint and posterior cruciate ligament (PCL)

  • Medially: Medial joint capsule and medial collateral ligament (MCL)

  • Laterally: Intercondylar notch structures including posterior cruciate ligament

Function

  • Distributes load across the medial tibiofemoral compartment

  • Provides joint congruency and shock absorption

  • Stabilizes the knee, especially against anterior translation in synergy with the ACL and PCL

  • Enhances lubrication and nutrition of articular cartilage

  • Acts as a secondary stabilizer in rotation and flexion

Clinical Significance

  • The most common site of meniscal tears, particularly posterior horn root tears and degenerative flap tears

  • Tears can cause pain, swelling, locking, or giving way of the knee

  • MRI is the gold standard for detection; arthroscopy remains the reference standard

  • Posterior horn meniscal tears are often associated with ACL injuries and early osteoarthritis

  • Repair is crucial as untreated root tears may accelerate medial compartment degeneration

MRI Appearance

T1-weighted images:

  • Posterior horn normally shows low signal intensity (dark)

  • Tears appear as linear or complex high-signal intensity extending to the articular surface

  • Meniscal cysts may appear adjacent with intermediate to bright signal

T2-weighted images:

  • Normal meniscus remains dark (low signal)

  • Tears appear as linear bright signal extending to articular surface

  • Fluid-sensitive T2 highlights meniscal degeneration or edema

STIR (Short Tau Inversion Recovery):

  • Meniscus remains dark

  • Edema, parameniscal cysts, or joint effusion appear bright hyperintense

Proton Density Fat-Saturated (PD FS):

  • Normal posterior horn: dark, homogeneous signal

  • Tears: linear or irregular bright signal, often extending to tibial or femoral surface

  • Excellent for subtle tears and root detachments

T1 Fat-Sat Post-Contrast:

  • Normal meniscus enhances minimally

  • Postoperative scar or synovitis shows contrast enhancement

  • Distinguishes recurrent tears (non-enhancing) from scar tissue (enhancing)

3D T2 SPACE / CISS:

  • Posterior horn appears as uniform dark structure with sharp margins

  • Fluid and cartilage appear bright, highlighting meniscal tears and root pathology

MRI Arthrogram Appearance

  • Direct MR arthrography: Contrast outlines meniscal tears with bright signal intensity entering the tear cleft

  • Helps differentiate true tears from intrasubstance degeneration

  • Root avulsions and small flap tears are better detected with intra-articular contrast

CT Appearance

Non-Contrast CT:

  • Meniscus not directly visualized (soft tissue density similar to cartilage)

  • Indirect signs of injury: joint space narrowing, subchondral sclerosis, osteophytes

Post-Contrast CT (standard):

  • Meniscus remains poorly defined without intra-articular contrast

  • Soft tissue changes may be inferred but not directly evaluated

CT Arthrogram Appearance

  • Meniscal tears appear as contrast-filled linear clefts within the posterior horn

  • Extravasation of contrast indicates complex or displaced tears

  • Particularly useful for patients who cannot undergo MRI

  • Superior to conventional CT for cartilage and meniscal evaluation

MRI image

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

MRI image

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

MRI image

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