Morrant Baker’s Cyst

MORRANT BAKER’S CYST (BAKER’S CYST)

Aetiopathogenesis:

• “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”- Mayerding and Van Denmark
• 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
• Cysts are connected to the knee joint through valvular opening.
• 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.
• A dissecting popliteal cyst can be the presenting feature of a malfunctioning total knee arthroplasty
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
• The cyst can extend into the thigh or legs and can have multiple satellite cysts all along the leg, which may or may not be connected
• A dissecting popliteal cyst may mimic acute thrombophlebitis (or deep vein thrombosis), where the calf is painful and swollen, and the Homan sign is positive-“pseudothrombophlebitis syndrome”
• Rarely, a dissecting popliteal cyst may coexist with popliteal vein thrombosis
• Rarely can cause compartment syndrome, peripheral neuropathy, calf, foot and ankle ecchymoses, septic arthritis of the knee if it gets infected.

Investigations:
• X-rays should be taken to rule out other causes of swelling in the popliteal fossa. For e.g., soft tissue calcifications may indicate the presence of a synovial sarcoma or a hemangioma
• 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

Ref:
1. Dirschl DR, Lachiewicz PF: Dissecting popliteal cyst as the presenting symptom of a malfunctioning total knee arthroplasty: a report of four cases. J Arthroplasty 1992; 7:37
2. Ko SH, Ahn JH: Popliteal cystoscopic excisional debridement and removal of capsular fold of valvular mechanism of large recurrent popliteal cyst. Arthroscopy 2004; 20:37.
3. Meyerding HW, Van Demark RE: Posterior hernia of the knee (Baker’s cyst, popliteal cyst, semimembranosus bursitis, medial gastrocnemius bursitis and popliteal bursitis). JAMA 1943; 122:858
4. Takahashi M, Nagano A: Arthroscopic treatment of popliteal cyst and visualization of its cavity through the posterior portal of the knee. Arthroscopy 2005; 21:638.
5. Curl WW: Popliteal cysts: historical background and current knowledge. J Am Acad Orthop Surg 1996; 4:129.