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Meniscus

Topic updated on 07/21/14 10:06pm
Function
  •  Force transmission
    • the meniscus functions to optimize force transmission across the knee. It does this by
      • increasing congruency
        • increases contact area leads to decreased point loading
      • shock-absorption
        • the meniscus is more elastic than articular cartilage, and therefore absorbs shock
      • transmits 50% weight-bearing load in extension, 85% in flexion
  • Stability
    • the meniscus deepens tibial surface and acts as secondary stabilizer
      • medial meniscus
        • posterior horn of medial meniscus is the main secondary stabilizer to anterior translation
      • lateral meniscus
        • is less stabilizing and has 2X the excursion of the medial meniscus
    • the menisci become primary stabilizers in the ACL-deficient knee
Composition
  • Made of fibroelastic cartilage
    • interlacing network of collagen, proteoglycan, glycoproteins, and cellular elements
    • composed of 65-75% water
  • Collagen
    • 90 % Type I collagen
  • Fibers
    • composed of two types of fibers which allow the meniscus to expand under compressive forces and increase contact area of the joint
      • radial
      • longitudinal (circumferential)
        • help dissipate hoop stresses
        • vertical mattress captures
Anatomy
  • Gross Shape
    • medial meniscus
      • C-shaped with triangular cross section
      • avarage width of 9 to 10mm
      • average thickness of 3 to 5mm
    • lateral meniscus
      • is more circular (the horns are closer together and approximate the ACL)
      • covers a larger portion of the articular surface
      • average width is 10 to 12mm
      • average thickness is 4 to 5mm
  • Attachment
    • transverse (intermeniscal) ligament
      • connects the medial and lateral meniscus anteriorly
    • coronary ligaments
      • connects the meniscus peripherally
      • medial meniscus has less mobility with more rigid peripheral fixation than the lateral meniscus 
    • meniscofemoral ligament 
      • connects the meniscus into the substance of the PCL
      • originate from the posterior horn of the lateral meniscus and has two components
        • Humphrey ligament (anterior) Humphrey Ligament
        • Ligament of Wrisberg (posterior)
  • Blood supply
    • medial inferior genicular artery
      • supplies peripheral 20-30% of medial meniscus
    • lateral inferior genicular artery
      • supplies peripheral 10-25% of lateral meniscus
      • central 75% receive nutrition through diffusion
  • Innervation
    • peripheral two-thirds innervated by Type I and II nerve endings
    • posterior horns have highest concentration of mechanoreceptors
Injury & Healing potential
  • See topic Meniscal Pathology 
  • Tears in peripheral 25% red zone
    •  can heal via fibrocartilage scar formation
      • fibrochondrocyte is cell responsible for healing
      • peripheral tears < 4 mm have best healing potential
  • Tears of central 75% 
    • have limited or no intrinsic healing ability

 

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(SBQ07.34) Which of the following is true when comparing the medial mensicus to the lateral meniscus? Topic Review Topic

1. More anterior translation with extension and less posterior movement with flexion
2. Less anterior translation with extension and posterior movement with flexion
3. More posterior translation with extension
4. More anterior translation with flexion
5. Less capsular attachments to the meniscus periphery

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