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 ‚
DIAGNOSIS
HISTORY
- Painless mass arising in the popliteal fossa
- Most cysts are asymptomatic.
- Dull ache if cyst is large enough to impede joint motion " ”typically a restriction of flexion
- Painful if cyst ruptures
- Large cysts may cause entrapment neuropathy of the tibial nerve.
- Vascular compression, most commonly of the popliteal vein, may produce claudication or thrombophlebitis.
- Activity alters the cyst size.
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.
- 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.
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].
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.
COMPLICATIONS
- Compartment syndrome in ruptured cyst
- Thrombophlebitis from compression of the popliteal vein
- Infection of popliteal cyst
- Hemorrhage into cyst if on anticoagulants
REFERENCES
11 Marra ‚ MD, Crema ‚ MD, Chung ‚ M, et al. MRI features of cystic lesions around the knee. Knee. 2008;15(6):423 " “438.22 Liao ‚ ST, Chiou ‚ CS, Chang ‚ CC. Pathology associated to the Baker 's cysts: a musculoskeletal ultrasound study. Clin Rheumatol. 2010;29(9):1043 " “1047.33 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 " “146.44 Roberts ‚ JR. Distinguishing Baker 's cyst from DVT. Emer Med News. 2003:25(11):14 " “16.55 Sanchez ‚ JE, Conkling ‚ N, Labropoulos ‚ N. Compression syndromes of the popliteal neurovascular bundle due to Baker cyst. J Vasc Surg. 2011;54(6):1821 " “1829.66 Acebes ‚ JC, S ƒ ¡nchez-Pernaute ‚ O, D ƒ az-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 " “117.77 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 " “567.88 Centeno ‚ CJ, Schultz ‚ J, Freeman ‚ M. Sclerotherapy of Baker 's cyst with imaging confirmation of resolution. Pain Physician. 2008;11(2):257 " “261.99 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 " “115.1010 Lie ‚ CW, Ng ‚ TP. Arthroscopic treatment of popliteal cyst. Hong Kong Med J. 2011;17(3):180 " “183.1111 Chen ‚ JC, Lu ‚ CC, Lu ‚ YM, et al. A modified surgical method for treating Baker 's cyst in children. Knee. 2008;15(1):9 " “14.1212 Handy ‚ JR. Popliteal cysts in adults: a review. Semin Arthritis Rheum. 2001;31(2):108 " “118.
ADDITIONAL READING
- 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
Algorithm: Knee Pain ‚
CODES
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
ICD9
- 727.51 Synovial cyst of popliteal space
SNOMED
- 82675004 Synovial cyst of popliteal space (disorder)
- 270887007 Rupture of popliteal space synovial cyst (disorder)
- 322221000119102 Synovial cyst of left popliteal space (disorder)
- 322231000119104 Synovial cyst of right popliteal space (disorder)
CLINICAL PEARLS
- 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.