Updated: 10/6/2016

Meniscal Cysts

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Overview
  • A condition characterized by a local collection of synovial fluid within or adjacent to the meniscus
  • Epidemiology
    • incidence
      • no studies of the general population
      • found in 1-4% of MRI studies of the knee
    • demographics
      • most commonly associated with a meniscal tear
      • no trend to increased age
    • location 
      • perimeniscal cysts 
        • small lesions of fluid within the meniscus
        • medial cysts are slightly more common than lateral, 2:1 ratio (although literature data are conflicting)
          • medial cysts = posterior horn
          • lateral cysts = anterior horn or mid-portion
      • parameniscal cysts (e.g., baker cysts)
        • extruded fluid outside the meniscus (most common)
        • usually located between semimembranosus and medial head of gastrocnemius 
  • Pathophysiology
    • mechanism of injury
      • meniscal tear functions as a one-way valve
      • synovial fluid extrudes and then concentrates to form gel-like material
    • pathoanatomy
      • horizontal and complex tears, usually = parameniscal cysts
      • radial or vertical tears, usually = perimeniscal cysts
  • Associated conditions
    • articular cartilage injury
    • anterior cruciate ligament tear
Anatomy
  • Meniscus
    • composition
      • fibroelastic cartilage
        • interlacing network of collagen, proteoglycan, glycoproteins, and cellular elements
        • composed of 65-75% water
      • Collagen
        • 90 % Type I collagen
    • shape
      • medial meniscus
        • stretched-out, C-shape with triangular cross section
      • lateral meniscus
        • more circular in shape
        • covers larger area of articular surface
    • Blood supply
      • medial inferior genicular artery
        • supplies peripheral 20-30% of medial meniscus
      • lateral inferior genicular artery
        • supplies peripheral 10-25% of lateral meniscus
      • synovial fluid
        • central 75% of meniscus' receive nutrition through diffusion
Presentation
  • History
    • may have recent trauma
  • Symptoms
    • asymptomatic
    • pain
      • localized to medial/lateral joint line or back of knee
    • mechanical symptoms
      • locking and clicking
    • delayed or intermittent knee swelling
    • weakness or claudication (neaurovascular impingement)
  • Examination
    • inspection
      • popliteal mass
      • best visualized with the knee in extension
    • palpation
      • joint line tenderness
      • palpable mass
    • motion
      • crepitus
 Imaging
  • Radiographs
    • should be normal in young patients with an acute meniscal injury or cyst
  • MRI    
    • indications
      • MRI is most sensitive diagnostic test for meniscal cyst and meniscal tear
    • findings
      • cyst with bright T2 signal
      • necrotic tissue, nerve sheath tissue, and pus can all resemble cysts on T2-weighted MRIs
      • IV contrast enhancement may be needed
Treatment
  • Non-operative
    • rest, NSAIDS, rehabilitation
      • indications
        • indicated as first line of treatment for small perimeniscal cysts and parameniscal cysts
      • outcomes
        • trial of medical therapy to observe patients pain response
        • may be effective in population with degenerative tears
    • aspiration and steroid injection
      • indication
        • isolated baker's cysts in young patient
      • technique
        • cyst drainage
        • ultrasound guided injection into the cyst
      • outcomes
        • poor outcomes in older degenerative mensical tears with associated cysts
  • Operative
    • arthroscopic debridement, cyst decompression and meniscal resection
      • indications
        • perimeniscal cysts with an associated tear that is not amenable to repair (e.g., complex, degenerative, radial tear patterns)
      • technique
        • decompress cyst completely
        • perform partial meniscectomy
      • outcomes
        • incomplete meniscal resection may lead to recurrence
    • cyst excision using open posterior approach
      • indications
        • symptomatic parameniscal cysts
      • outcomes
        • incomplete resection may lead to recurrence
Technique
  • Cyst excision using open posterior approach
    • patient prone
    • curved incision over popliteal fossa
    • interval between medial head of gastrocnemius and semimembranosus
    • sharp dissection of cyst margins to joint capsule

 

 

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