Baker’s cyst – Causes, Symptoms, Diagnosis, Treatment and Ongoing care
- A fluid-filled synovial sac arising in the popliteal fossa
- Distention of the gastrocnemial-semimembranous bursa
- Can be unilateral or bilateral
- Primary cysts are a distention of the bursa arising independently without an intra-articular disorder
- Secondary cysts occur if a communication exists between the bursa and knee joint, allowing articular fluid to fill the cyst. Pathologic joint processes can also be transmitted in this manner.
- Associated with synovial inflammation
- Synonym: Popliteal cyst
- Bimodal distribution: Children ages 4–7, and adults increasing with age
- Primary cysts usually seen in children under 15 years of age
- Secondary cysts seen in the adult population
- Varies by study
- Studies report a prevalence of 19–47% in symptomatic knees, 2–5% in asymptomatic knees
- In children, 6.3% in symptomatic knees, 2.4% in asymptomatic knees
- Osteoarthritis of knee (most common) (1)[B]
- Rheumatoid arthritis
- Meniscal degeneration or tear
- Advancing age
- Ligamentous insufficiency
- Extension or herniation of synovial membrane of the knee joint capsule or connection of normal bursa with the joint capsule
- May be the result of increased intra-articular pressure
- Commonly seen with knee effusions
- Direct trauma to the bursa likely the primary cause in children since there is no communication between the bursa and the joint in children
- A valve-like mechanism allowing one-way passage of fluid from the joint to the bursal connection has been described.
Associated intra-articular pathological findings include:
- Meniscal tears, posterior horn
- ACL insufficiency
- Degenerative articular cartilage lesions
- Rheumatoid arthritis
- Other potential factors: Infectious arthritis, polyarthritis, villonodular synovitis, and connective tissue diseases
Commonly Associated Conditions
Any condition causing knee joint effusion
- Painless mass arising in the popliteal fossa
- Most cysts are asymptomatic
- Painful if cyst ruptures
- May report restricted range of motion or tightness with knee flexion
- Large cysts may cause entrapment neuropathy of the tibial nerve.
- Vascular compression, most commonly of the popliteal vein, may produce claudication or thrombophlebitis.
- Activity will alter the cyst size.
- Examine in full extension and 90° of flexion
- Foucher sign: Mass increases with extension and disappears with flexion.
- Most commonly found in medial aspect of popliteal fossa lateral to the head of the gastrocnemius and medial to the neurovascular bundle.
- Mass may be fluctuant or tender.
- Transillumination can distinguish cyst from solid mass.
- Ruptured cyst typically painful with associated swelling over calf and medial malleolus, pseudothrombophlebitis
Diagnostic Tests & Interpretation
Initial lab tests
- CBC, sedimentation rate if suspicious of septic arthritis
- Send aspirate for cell count to determine nature of effusion: Infectious, inflammatory, or mechanical.
Follow-Up & Special Considerations
In children, consider observation before invasive testing.
- Ultrasound confirms presence and size; with Doppler can differentiate Baker cysts from popliteal vessel aneurysms or soft tissue tumors (2)[B].
- MRI is useful to assess for causal derangements of internal joint structures.
- Radiographs may show soft tissue density posteriorly.
- Arthrography may demonstrate communication with joint capsule, or rupture.
- CT–arthrography together is superior in visualizing cystic details and can help separate lipomas, aneurysms, and malignancies from cysts.
- Deep venous thrombosis
- Vascular tumor
- Popliteal vein varices
- Aneurysm (rare)
- Ganglion cyst
- Any condition causing synovitis
- Muscular herniation (rare, related to trauma)
- Once etiology is identified from cellular fluid examination, treat the underlying condition
- Analgesics, NSAIDS for symptomatic relief
- No treatment if cyst is asymptomatic
- Compressive wrap or sleeve may be used for comfort
- Physical therapy improves knee range of motion and strength, particularly with coexisting pathology
- Temporary relief with needle aspiration, recurrence common
- Improvement in joint range of motion, knee pain, swelling, accompanied reduction in bursa size has been shown after intra-articular or intracystic corticosteroid injection (2)[B]
- Sclerotherapy injections of ethanol or dextrose/sodium morrhuate shown to have good results in studies with small sample sizes (3)[B]
- Consider excision when symptoms persist despite treatment or no etiology is found.
- Recurrence after standard surgery is common and is highest when chondral lesions are present (4)[B].
- A modified surgical technique in children has been proven effective without recurrence (5)[B].
- Excision via arthroscopy or open procedure often requires concomitant treatment of underlying pathology (6)[B].
- Many cysts remain asymptomatic.
- Some will regress or resolve with treatment of underlying etiology
- In children, most resolve without treatment.
- Compartment syndrome in ruptured cyst
- Thrombophlebitis from compression of the popliteal vein
- Infection of popliteal cyst
- Hemorrhage into cyst if on anticoagulants
1. Chatzopoulos D, Moralidis E, Markou P, et al. Baker’s cysts in knees with chronic osteoarthritic pain: a clinical, ultrasonographic, radiographic and scintigraphic evaluation. Rheumatol Int. 2008 Jun 27.
2. Acebes JC, Sanchez-Pernaute O, Diaz-Oca A, et al. Ultrasonographic Assessment of Baker’s Cysts after Intra-articular Corticosteroid Injection in Knee Osteoarthritis. J Clin Ultrasound. 2006;34:113–7.
3. Centeno CJ, Schultz J, Freeman M, et al. Sclerotherapy of Baker’s Cyst with Imaging Confirmation of Resolution. Pain Physician. 2008;11:257–61.
4. Rupp S, Seil R, et al. Popliteal cysts in adults: Prevalence, associated intraarticular lesions, and results after arthroscopic treatment. Am Sport Med. 2002;30(1):112–5.
5. Chen J-C, Cheng-Chang L, Lu Y-M, et al. A modified surgical method for treating Baker’s cyst in children. The Knee. 2008;15:9–14.
6. Handy JR. Popliteal cysts in adults: A review. Semin Arthritis Rheu. 2001;31(2):108–18.
Fritschy D, Fasel J, Imbert J, et al. The popliteal cyst. Knee Surg Sports Traumatol Arthosc. 2006;14:623–8.
Marra MD, Crema MD, Chung M, et al. MRI features of cystic lesions around the knee. The Knee. 2008 Jun 16.
Seil R, Rupp S, et al. Prevalence of popliteal cysts in children: A sonographic study and review of the literature. Arch Ortho Traum Su. 1999;119:73–5.
Van Rhijn L, Jansen E, Pruijs H. Long term follow up of conservatively treated popliteal cysts in children. Journal of Pediatric Orthopedics Part B. 2000;9:62–64.
See Also (Topic, Algorithm, Electronic Media Element)
Algorithm: Knee Pain
727.51 Synovial cyst of popliteal space
82675004 Synovial cyst of popliteal space (disorder)
- In children, it is acceptable to wait and observe.
- Treat underlying cause.
- Pain and swelling over the medial malleolus is classic for cyst rupture, also known as pseudothrombophlebitis.