> Table of Contents > Popliteal (Baker) Cyst
Popliteal (Baker) Cyst
Shane L. Larson, MD
image BASICS
DESCRIPTION
  • A fluid-filled synovial sac arising in the popliteal fossa as a distention of (typically) the gastrocnemial-semimembranous bursa. Not a true cyst
  • Can be unilateral or bilateral
  • Most frequent cystic mass around the knee (1)
  • Primary cysts are a distention of the bursa (arise independently without an intra-articular disorder).
  • Secondary cysts occur if there is a communication between the bursa and knee joint, allowing articular fluid to fill the cyst.
  • Associated with synovial inflammation
EPIDEMIOLOGY
Incidence
  • Bimodal distribution
    • Children ages 4 to 7 years
    • Adults increasing with age
  • Primary cysts usually seen in children <15 years
  • Secondary cysts seen in adults
Prevalence
  • Variable adult prevalence of 19-47% in symptomatic knees and 2-5% in asymptomatic knees.
  • In children: 6.3% in symptomatic knees; 2.4% in asymptomatic knees
ETIOLOGY AND PATHOPHYSIOLOGY
Associated intra-articular pathology includes
  • Meniscal tears, mostly of the posterior horn
  • Anterior cruciate ligament (ACL) insufficiency
  • Degenerative articular cartilage lesions
  • Rheumatoid arthritis (20%)
  • Osteoarthritis (50%)
  • Osteochondritis
  • Gout (14%)
  • Other potential factors
    • Infectious arthritis
    • Polyarthritis
    • Villonodular synovitis
    • Lymphoma
    • Sarcoidosis
    • Connective tissue diseases (2)
  • Extension or herniation of synovial membrane of the knee joint capsule or connection of normal bursa with the joint capsule
  • May result from increased intra-articular pressure
  • Commonly seen with knee effusions
  • Direct trauma to the bursa is likely the primary cause in children because of no communication between the bursa and the joint.
  • A valve-like mechanism allowing one-way passage of fluid from the joint to the bursal connection has been described.
RISK FACTORS
  • Osteoarthritis of knee (most common) (3)[B]
  • Rheumatoid arthritis
  • Meniscal degeneration or tear
  • Advancing age
  • Ligamentous insufficiency
COMMONLY ASSOCIATED CONDITIONS
Any condition causing knee joint effusion
image DIAGNOSIS
PHYSICAL EXAM
  • Examine in full extension and 90 degrees 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
  • Cyst is easiest to palpate when knee is slightly flexed and may occasionally be fluctuant or tender.
  • Transillumination helps distinguish cyst from solid mass.
  • Ruptured cysts are typically painful with associated swelling and bruising over the ipsilateral calf and ankle at the medial malleolus (Crescent sign).
  • Ruptured cysts also are associated with pseudothrombophlebitis, and rarely, compartment syndrome (5).
DIFFERENTIAL DIAGNOSIS
  • Infection/abscess
  • Lipoma, liposarcoma
  • Fibroma, fibrosarcoma
  • Hematoma
  • Deep venous thrombosis
  • Vascular tumor
  • Popliteal vein varices
  • Xanthoma
  • Aneurysm (rare)
  • Ganglion cyst
  • Thrombophlebitis
  • Muscular herniation (rare, related to trauma)
DIAGNOSTIC TESTS & INTERPRETATION
Initial Tests (lab, imaging)
  • CBC, ESR (if septic arthritis suspected)
  • Ensure not a popliteal aneurysm prior to aspiration. Send aspirate for cell count and culture to determine if fluid is infectious, inflammatory, or mechanical.
  • Ultrasound confirms presence and size; Doppler, can differentiate Baker cysts from popliteal vessel aneurysms, DVT, or soft tissue tumors (4).
  • MRI helps assess derangements of internal joint structures and to identify cyst leakage.
Follow-Up Tests & Special Considerations
  • Consider observation over invasive testing in children.
  • Radiographs may show soft tissue density posteriorly.
  • P.831

  • Arthrography may demonstrate communication with joint capsule or rupture.
  • CT arthrography is superior for visualizing cystic details and can help distinguish lipomas, aneurysms, and malignancies from cysts.
image TREATMENT
GENERAL MEASURES
  • No treatment if asymptomatic
  • Treat any associated underlying conditions.
  • Compressive wrap or sleeve for comfort.
MEDICATION
If etiology is identified from cellular fluid examination, treat the underlying condition.
First Line
Analgesics and NSAIDs for symptomatic relief
ADDITIONAL THERAPIES
  • Physical therapy improves knee ROM and strength, particularly with coexisting pathology.
  • Temporary relief with needle aspiration; recurrence common
  • Improvement in joint ROM, knee pain, swelling, accompanied reduction in bursa size after aspiration, and intra-articular/intracystic corticosteroid injection (6)[B]
  • A combination of physical therapy and corticosteroid injection leads to best improvements in pain, function, and reduction in cyst size (7)[A].
  • Sclerotherapy injections of ethanol or dextrose/sodium morrhuate shown to have good results in small studies (8)[B].
SURGERY/OTHER PROCEDURES
  • Consider excision when symptoms persist despite treatment or no etiology is found.
  • Surgery usually not required in children
  • Recurrence after standard surgery is common and is highest if chondral lesions are present.
  • Arthroscopic surgery is highly successful if a valvular mechanism is identified and intra-articular pathology is treated (9,10)[B].
  • A modified surgical technique in children has proved effective without recurrence (11)[B].
  • Excision via arthroscopy or open procedure often requires concomitant treatment of underlying pathology (12)[B].
image ONGOING CARE
PROGNOSIS
  • Variable; many cysts remain asymptomatic.
  • Some cysts resolve with treatment of underlying etiology (e.g., gout, rheumatoid arthritis).
  • In children, most cysts resolve without treatment.
REFERENCES
1. Marra MD, Crema MD, Chung M, et al. MRI features of cystic lesions around the knee. Knee. 2008;15(6):423-438.
2. Liao ST, Chiou CS, Chang CC. Pathology associated to the Baker's cysts: a musculoskeletal ultrasound study. Clin Rheumatol. 2010;29(9):1043-1047.
3. 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;29(2):141-146.
4. Roberts JR. Distinguishing Baker's cyst from DVT. Emer Med News. 2003:25(11):14-16.
5. Sanchez JE, Conkling N, Labropoulos N. Compression syndromes of the popliteal neurovascular bundle due to Baker cyst. J Vasc Surg. 2011;54(6):1821-1829.
6. Acebes JC, Sánchez-Pernaute O, Díaz-Oca A, et al. Ultrasonographic assessment of Baker's cysts after intra-articular corticosteroid injection in knee osteoarthritis. J Clin Ultrasound. 2006;34(3):113-117.
7. Di Sante L, Paoloni M, Dimaggio M, et al. Ultrasound-guided aspiration and corticosteroid injection compared to horizontal therapy for treatment of knee osteoarthritis complicated with Baker's cyst: a randomized, controlled trial. Eur J Phys Rehabil Med. 2012;48(4):561-567.
8. Centeno CJ, Schultz J, Freeman M. Sclerotherapy of Baker's cyst with imaging confirmation of resolution. Pain Physician. 2008;11(2):257-261.
9. Rupp S, Seil R, Jochum P, et al. Popliteal cysts in adults. Prevalence, associated intraarticular lesions, and results after arthroscopic treatment. Am J Sports Med. 2002;30(1):112-115.
10. Lie CW, Ng TP. Arthroscopic treatment of popliteal cyst. Hong Kong Med J. 2011;17(3):180-183.
11. Chen JC, Lu CC, Lu YM, et al. A modified surgical method for treating Baker's cyst in children. Knee. 2008;15(1):9-14.
12. Handy JR. Popliteal cysts in adults: a review. Semin Arthritis Rheum. 2001;31(2):108-118.
Additional Reading
&NA;
  • Akagi R, Saisu T, Segawa Y, et al. Natural history of popliteal cysts in the pediatric population. J Pediatr Orthop. 2013;33(3):262-268.
  • Akgul O, Guldeste Z, Ozgocmen S. The reliability of the clinical examination for detecting Baker's cyst in asymptomatic fossa. Int J Rheum Dis. 2014;17(2):204-209.
See Also
&NA;
Algorithm: Knee Pain
Codes
&NA;
ICD10
  • M71.20 Synovial cyst of popliteal space [Baker], unspecified knee
  • M71.21 Synovial cyst of popliteal space [Baker], right knee
  • M71.22 Synovial cyst of popliteal space [Baker], left knee
Clinical Pearls
&NA;
  • Conservative treatment of Baker cysts is preferred in children, as most will spontaneously resolve.
  • In adults, treatment of underlying cause may resolve Baker cysts.
  • Pain, bruising, and swelling over the medial malleolus (crescent sign) suggests cyst rupture.