Meniscus injury and tear

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Mechanism of meniscus tear and misdiagnosed structural manifestations, including different types of tears and MRI appearances. Meniscus root tears are also important diagnostic content. The McMurray test and compression grinding test are also part of the diagnosis.

Mechanism of Meniscus Tear

• The medial meniscus is narrow anteriorly and wide posteriorly, thin in front and thick in back, designed to limit excessive anterior tibial translation and rotation. Meniscus tears often occur in the posterior horn; isolated anterior meniscus tears are rare.
• Anterior cruciate ligament injuries are often accompanied by medial meniscus posterior horn injuries (tearing the posterior horn when the femur moves backward).

Normal Structures or Manifestations Misdiagnosed as Meniscus Tear

• Meniscus grade 2 injury (degeneration): abnormal signal reaching the joint capsule margin, not reaching the articular surface margin

  

• Capillary sign or ligament insertion within the meniscus

  

• Parameniscal cyst-like meniscus: rare, can be a normal variant; such manifestations may also appear in meniscus tears

  

• Transverse meniscal ligament: originates from the anterior horn or anterior margin of the medial meniscus, runs transversely outward and ends at the anterior convex margin of the lateral meniscus. Thick at both ends and thin in the middle. It is easily misdiagnosed as anterior horn meniscus tear. Continuous observation shows the ligament running between the two meniscus anterior horns.

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• Meniscofemoral ligaments,

  • A small ligament from the posterior horn of the lateral meniscus fixed to the lateral surface of the medial femoral condyle. This ligament passes either anterior or posterior to the PCL. Located anteriorly is called the Humphry ligament (incidence 13.00%), located posteriorly is called the Wrisberg ligament (incidence 94.67%). Must not be mistaken for lateral meniscus posterior horn tear.
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• Popliteus tendon

  • Runs posterolaterally behind the posterior horn, should not be mistaken for a tear.
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Classification of Meniscus Tears

• Flap tear (oblique tear, horizontal tear)

  • Oblique (most common): tear line neither parallel nor perpendicular to the tibial plateau joint surface
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  • Horizontal: tear line is parallel to the tibial articular surface, mostly in the posterior horn or body of the meniscus (possibly due to horizontal posterior movement of the femur?), may be accompanied by a meniscal cyst
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    • Meniscal cyst (after meniscus tear, joint fluid enters the meniscus—the tear line communicates with the cyst)
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    • Flap tear (after oblique or horizontal tear, fragments run into the corner, meniscus becomes flap-shaped

• Longitudinal tear

  • Tear line is perpendicular to the tibial plateau joint surface, common in young athletes; horizontal displacement may form bucket-handle tears and fragment flipping tears
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  • Bucket-handle tear (a special type of longitudinal tear)
    • More common in the medial meniscus, incidence three times that of the lateral meniscus
    • The torn medial part displaces into the intercondylar notch; displaced meniscus appears as a bucket handle, nondisplaced meniscus represents the bucket
    • Fragment displacement sign, double posterior cruciate ligament sign; clinically more severe symptoms, easily causes joint locking
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  • Fragment flipping tear (after bucket-handle tear, the bucket handle rotates a circle)
    • Double anterior horn sign + posterior horn truncation sign or double posterior horn sign + anterior horn truncation sign
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• Radial tear

  • Tear line is perpendicular to the long axis of the meniscus, MR images are perpendicular to the tibial plateau joint surface, needs differentiation from longitudinal tear
  • Ranges from small lesions along the free edge of the meniscus to large tears penetrating the entire meniscus
  • Often involves the lateral meniscus
  • MRI manifestations: triangular truncation sign, cleft sign, directional change cleft sign, meniscus ghost sign
  • Triangular truncation sign: tear along anterior-posterior direction, entire meniscus is torn, the middle piece is cleft on all sequences
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  • Cleft sign (milder than triangular truncation sign, cleft only visible in sequences near intercondylar notch)
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  • Directional change cleft sign (neither anterior-posterior nor left-right tear, obliquely torn, so the cleft runs continuously across several sequences)
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  • Ghost sign (left-right tear; on sagittal view, intact meniscus appears black, torn area filled with fluid appears white)
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    • Comparison with fragment flipping tear
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• Meniscus root tear

  • The meniscus root is a special fibrous structure that fixes the anterior and posterior horns of the meniscus to the center of the tibial plateau, playing an important role in maintaining the normal position and function of the meniscus. Divided into anterior root and posterior root according to location.
  • Root injury refers to avulsion of the meniscus root tibial attachment point and radial tears within 1 cm of the bony attachment of the meniscus root.
  • Medial meniscus root injuries are more common than lateral meniscus root injuries.
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• [[Discoid Meniscus]]

Diagnosis

[[McMurray Test]]
[[Compression Grinding Test]]