Meniscal Cyst
What is a meniscal cyst?
  • A meniscal cyst is a localised collection of synovial fluid within or adjacent to the meniscus most commonly as a result of a meniscal tear

What types of meniscal cysts are there?
  • There are two types of meniscal cysts: 
    • Perimeniscal cysts: 
      • located within the meniscus
    • Parameniscal cysts: 
      • Located beyond the margins of the meniscus
      • Baker’s cyst is an example of one 
Aetiology
  • Perimeniscal cysts (which are considered here) are often associated with a meniscal tear typically a degenerative tear
  • The meniscal tear is thought to create a one-way valve mechanism:
    • Synovial fluid from the knee joint goes through the meniscal tear and into the cyst but cannot go back into the joint
  • However not all meniscal cysts are associated with a meniscal tear

What are the risk factors for meniscal cysts?
  • Risk factors are:
    • Twisting knee injury causing a meniscal tear
    • Previous knee injury such as ligament injury
    • Age, as this increases the chance of a degenerate meniscal tear

What are the most common locations for meniscal cysts?
  • 90% of meniscal cysts are located in the lateral meniscus:
    • Lateral meniscal cysts are usually anterior (front)
  • 10% of meniscal cysts are located in the medial meniscus:
    • Medial meniscal cysts are usually posterior (back)

How frequent are meniscal cysts?
  • Meniscal cysts are thought to occur in around 5% of the general population 
  • They are found in ~2% of MRI scans
Symptoms
  • Pain on the side of the knee joint line:
    • Especially when standing on the affected leg
  • Clicking
  • 40-60% of cysts are palpable
  • Knee swelling
  • Can be completely asymptomatic
Investigations
  • MRI scan is the gold standard:
    • Helps to identify size and location of cyst as well as any associated meniscal tear
  • Ultrasound scans can also be helpful 
Conservative treatment options for meniscal cyst
  • Anti-inflammatories:
    • They help to reduce inflammation and swelling in the knee
  • Rest:
    • This helps to reduce strain on the knee and subsequent swelling
  • Ice:
    • Frequent icing of the knee helps to reduce inflammation and swelling inside the knee
  • Compression with an elastic bandage:
    • Wrapping the knee up with an elastic bandage will help reduce knee swelling
  • Elevation:
    • Elevating the leg will help reduce knee swelling with the help of gravity
  • Ultrasound guided needle aspiration of cyst and injection of steroid:
    • Avoids risks of surgery
    • High risk of recurrence

Surgical treatment options for meniscal cyst
  • Knee arthroscopy and debridement of meniscal tear:
    • Aim is to disrupt one-way mechanism and allow free passage of synovial fluid in both directions
    • 90% of patients report good to excellent results
  • If the cyst is large or not communicating with meniscal tear, can be surgically removed from the outside
  • Meniscal tear where possible can be repaired with meniscal sutures to seal off the valve