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Updated: May 28 2021

Meniscal Cysts

  • summary
    • Meniscal cysts are a condition characterized by a local collection of synovial fluid within or adjacent to the meniscus most commonly as result of a meniscal tear.
    • Diagnosis is confirmed with MRI studies of the knee.
    • Treatment is generally nonoperative with physical therapy and NSAIDs. Surgical decompression with partial meniscectomy versus meniscus repair may be indicated for persistently symptomatic patients who fail conservative management. 
  • 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
    • Anatomic 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
  • Etiology
    • 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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