Baker's Cyst (Popliteal Cyst)

Classification by underlying cause:

Associated intra-articular pathology (independent MRI associations; Miller 1996, PMID 8816552):

• Joint effusion
• Meniscal tear
• Degenerative arthropathy (osteoarthritis)
• Inflammatory arthropathy and chronic synovitis (e.g. rheumatoid arthritis), PVNS and chondral injury are also recognised secondary causes

The probability of a cyst rises with the number of these co-existing features. The aetiology classification guides treatment - primary can be observed, secondary requires knee assessment.

Classification by clinical status:

Complicated cysts may require more aggressive intervention beyond treating the knee alone.

Classification by size:

Classification by extent:

• Localized: Confined to popliteal fossa
• Proximal extension: Along semimembranosus or gastrocnemius
• Distal extension: Dissecting into posterior calf compartments
• Multiloculated: Multiple compartments or septations

Size and extent influence risk of complications and treatment approach.

Ultrasound is the first-line imaging modality.

Ultrasound is excellent for confirming the diagnosis and excluding vascular pathology.

MRI is the gold standard for comprehensive assessment.

Plain X-rays have limited role.

Plain radiographs are useful to assess for arthritis but not diagnostic for Baker's cyst.

The choice of imaging depends on clinical presentation and need to assess underlying knee pathology.

Conservative management is first-line for most Baker's cysts.

Aspiration with or without corticosteroid injection.

Aspiration is palliative, not curative. It buys time but does not address the underlying problem.

Surgical excision is reserved for specific indications.

Outcomes of surgery:

• Isolated cyst excision: 40-60% recurrence
• Combined with treatment of knee pathology: Less than 10% recurrence
• Most patients have good symptom relief
• Return to activity in 4-6 weeks

The combined approach has the best outcomes with lowest recurrence risk.

Management of ruptured Baker's cyst (pseudothrombophlebitis).

The key is distinguishing from DVT - always do Doppler ultrasound.

Isolated cyst excision without treating knee pathology is not recommended due to high recurrence.

Safe exposure requires careful identification of neurovascular structures before proceeding.

Surgical steps for cyst excision:

Step 1: Identify neurovascular structures

• Tibial nerve runs lateral to the cyst (most at risk)
• Popliteal vessels run deep and lateral
• Common peroneal nerve is lateral (around fibular head)
• Protect these structures throughout

Step 2: Identify the cyst

• Usually posteromedial between gastrocnemius and semimembranosus
• May be multiloculated
• Carefully dissect investing fascia

Step 3: Mobilize the cyst

• Blunt dissection to separate cyst from surrounding structures
• Identify neck or stalk connecting to joint
• Trace proximally to capsular communication

Step 4: Ligate communication

• Critical step to prevent recurrence
• Identify stalk entering posteromedial joint capsule
• Ligate with heavy non-absorbable suture (e.g., 0 silk)
• Can use clips or suture ligature
• Tie securely to close communication

Step 5: Excise cyst

• Divide cyst distally to ligation
• Remove cyst completely
• Send for histopathology (confirm diagnosis, exclude malignancy)

Step 6: Hemostasis and closure

• Careful hemostasis (small vessels in area)
• Irrigate wound
• Close deep fascia (absorbable suture)
• Subcutaneous closure (absorbable)
• Skin closure (subcuticular or staples)

Arthroscopy plus open excision:

This is the preferred approach for most cases as it addresses both the cyst and underlying pathology.

Stage 1: Arthroscopy

• Standard diagnostic arthroscopy
• Identify and treat intra-articular pathology:
  • Meniscal tear (repair or partial meniscectomy)
  • Loose bodies (remove)
  • Chondral defects (debridement or microfracture)
  • Synovitis (synovectomy)
• Some surgeons identify and cauterize/close communication with cyst (controversial)

Stage 2: Reposition to prone

• Turn patient prone
• Re-prep and drape posterior knee

Stage 3: Open cyst excision

• As described above
• Ligate communication
• Excise cyst

This combined approach has the best outcomes with lowest recurrence.

Most patients recover fully within 6-8 weeks with low recurrence if knee pathology addressed.