Morrant Baker’s Cyst

• “A type of cyst which results from egress of fluid through a normal communication of a bursa (semimembranosus or medial gastrocnemius bursa) or caused by herniation of the synovial membrane through the joint capsule”

• Named after Baker (described it in 1877), though Adams had described it earlier in 1840.

• Symptoms develop in the bursa beneath the medial head of the gastrocnemius or in the semimembranosus bursa

• It develops due to chronic irritation, that increases the production of synovial fluid and distends one of the six bursae, commonly the medial gastrocnemius-semi membranous bursa

• Chronic irritation is commonly due to osteoarthritis or rheumatoid arthritis

• More common in adults than in children

• The aetiology for Popliteal cysts differ in children and adults

• An underlying intraarticular pathology is rare in children whereas in an adult an intraarticular pathology is usually evident (e.g., patellofemoral Chondromalacia or a degenerative tear of the posterior horn of the medial meniscus)

• Hence in adults the intraarticular pathology should be concurrently treated or it may recur.

Clinical Features:

• The popliteal cyst always transilluminates, often lying on the medial side of the popliteal fossa

• Foucher’s sign: with the patient prone, and the knee extended the swelling will appear prominent, but with knee flexion the swelling becomes soft and less prominent

Investigations:

• Aspiration confirms the diagnosis. Always rule out a vascular malformation from the popliteal artery prior to aspiration by auscultation for a bruit.

• Ultrasound helps to differentiate a cyst from other causes of swelling in the popliteal space (e.g., lipoma, xanthoma, vascular tumor, Fibrosarcoma)

• MRI and Arthrography also helps in establishing a diagnosis

Treatment:
• In children the cyst spontaneously resolves.

• In adults the cyst may be excised and the underlying pathology may be treated to
decrease the incidence of recurrence

• Arthroscopy should be performed prior to excision of popliteal cyst (patellofemoral chondromalacia or a degenerative tear of the posterior horn of the medial meniscus may be treated prior to excision of cyst)

• Hughston, Baker, and Mello’s posteromedial approach: made through a medial hockey-stick incision for excision of the cyst