Posterior Root of Medial Meniscus: Anatomy, Attachments, Relations, Function, Clinical Significance, MRI, CT & Arthrogram Imaging

Topic

Posterior root of medial meniscus

The posterior root of the medial meniscus is a short, thickened attachment anchoring the medial meniscus to the tibial plateau. It is critical for converting axial loads into hoop stresses, maintaining knee joint stability, and protecting articular cartilage. Injuries to this structure, particularly root tears, significantly alter knee biomechanics, causing meniscal extrusion, accelerated cartilage degeneration, and early osteoarthritis.

Synonyms

Medial meniscus posterior root
Posterior tibial attachment of medial meniscus
MM posterior horn root

Attachment and Relations

Attachment: Inserts into the posterior intercondylar area of the tibia, just anterior to the posterior cruciate ligament (PCL) tibial attachment
Relations:
- Anteriorly: Posterior cruciate ligament (PCL) tibial footprint
- Posteriorly: Tibial plateau margin and posterior capsule
- Medially: Medial tibial plateau and capsule of knee joint
- Laterally: Intercondylar notch and anterior cruciate ligament (ACL) tibial attachment (anterior to it)
- Superiorly: Femoral condyles during flexion/extension
- Inferiorly: Tibial plateau articular cartilage

Function

Anchors medial meniscus to tibial plateau
Converts compressive loads into circumferential hoop stresses
Provides stability to medial meniscus during weight-bearing and motion
Prevents extrusion of medial meniscus
Protects tibiofemoral articular cartilage

Clinical Significance

Root tears: Cause loss of meniscal function, leading to extrusion and rapid cartilage degeneration
Arthritis link: Posterior root tears are strongly associated with early medial compartment osteoarthritis
Surgical importance: Often require root repair or meniscal transplant to restore knee biomechanics
Imaging relevance: Root tears are frequently missed without dedicated MRI protocols

MRI Appearance

T1-weighted images:

Posterior root appears as a low-signal intensity band attaching medial meniscus to tibia
Surrounded by bright fat for contrast
Root tears appear as discontinuity, truncation, or ghost meniscus sign

T2-weighted images:

Normal root is dark (low-signal intensity)
Root tears: bright fluid signal intensity within attachment site, loss of normal dark band
Associated findings: meniscal extrusion, subchondral bone marrow edema

STIR (Short Tau Inversion Recovery):

Root normally low-signal
Root tears and adjacent edema: bright hyperintensity
Sensitive for inflammatory or post-traumatic changes

Proton Density Fat-Saturated (PD FS):

Normal root: low-signal intensity
Root tear: bright hyperintensity, well-demarcated against fat-suppressed background
Best sequence for subtle root pathology

T1 Fat-Sat Post-Contrast:

Normal root shows no significant enhancement
Post-surgical changes or inflammatory synovitis may show enhancement around the root attachment

MRI Arthrogram Appearance

Normal root: intact, low-signal attachment without contrast leakage
Root tear: intra-articular contrast extends into tibial attachment site, highlighting discontinuity or detachment
Better delineates subtle or partial tears compared to conventional MRI

CT Appearance

Non-Contrast CT:

Root itself not well visualized
Secondary findings may include joint space narrowing, osteophytes, or bony sclerosis in chronic pathology
Occasionally calcification at root insertion

Post-Contrast CT:

Direct visualization of root is limited
Useful for detecting associated osseous pathology or surgical anchors

CT Arthrogram Appearance

Normal root: intact low-density band, no contrast entering root insertion
Root tear: contrast penetrates root attachment site or extravasates beneath tibial plateau
Clearly demonstrates partial or complete root avulsions

MRI image

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