Baker's Cyst


Article Author:
Ari Leib
Afghania Roshan
Lisa Foris


Article Editor:
Matthew Varacallo


Editors In Chief:
Sisira Reddy
Joseph Nahas
Chokkalingam Siva


Managing Editors:
Avais Raja
Orawan Chaigasame
Khalid Alsayouri
Kyle Blair
Radia Jamil
Erin Hughes
Patrick Le
Anoosh Zafar Gondal
Saad Nazir
William Gossman
Hassam Zulfiqar
Navid Mahabadi
Hussain Sajjad
Steve Bhimji
Muhammad Hashmi
John Shell
Matthew Varacallo
Heba Mahdy
Ahmad Malik
Sarosh Vaqar
Mark Pellegrini
James Hughes
Beenish Sohail
Hajira Basit
Phillip Hynes
Sandeep Sekhon


Updated:
11/7/2019 2:25:11 PM

Introduction

A Baker Cyst, also known as a popliteal or parameniscal cyst, is a fluid-filled sac that forms in the posterior aspect of the knee, typically located between the semimembranosus and medial head of the gastrocnemius. [1][2][3]

In adults, Baker's Cysts tend to form in association with degenerative conditions of the knee.  One of the most common associations is seen secondary degenerative meniscal tears.  Inflammatory conditions and arthritides are also known causes of popliteal cyst formation.  When the cyst forms in association with a meniscal tear, the meniscus serves as a one-way valve and the extruded synovial fluid localizes and consolidates to form a viscous, gel-like material.

In children, popliteal cysts more commonly arise as a primary condition.  Unliked adults, popliteal cysts in children arise from a herniated posterior knee joint synovium/capsule.

Etiology

Baker's cysts are encountered most frequently in adults with a history of trauma (e.g., cartilage or meniscus tears, injury to the knee), in association with degenerative/co-existing knee joint disease (e.g., osteoarthritis, rheumatoid arthritis, infectious arthritis, pigmented villonodular synovitis, meniscal tears), or .asymptomatically as an incidental finding.[4]

Baker's cysts form and can expand as a result of the accumulation and extrusion of synovial fluid that localizes between the semimembranosus and medial head of the gastrocnemius.  In some instances, normal anatomic variants entail physiologic capsular openings or defects in the posterior knee joint capsule that is essentially contiguous with the gastrocnemius-semimembranosus bursa.  Popliteal cysts are located on the medial side of the popliteal fossa just below the crease found at the posterior knee.

Epidemiology

Baker's cysts tend to occur most commonly in adults aged 35 to 70 and most often are associated with inflammatory joint diseases such as rheumatoid arthritis, osteoarthritis, or as a result of overuse or injury to the knee. As they are asymptomatic, Baker's cysts are most often detected incidentally on physical examination or imaging studies (e.g., MRI in an adult with suspected osteoarthritis or internal abnormalities of the knee). Prevalence typically increases with age, most likely due to the increase in knee-bursal communication with age.[5]

In children, Baker's Cysts tend to occur most frequently in those aged 4 to 7 years.

Pathophysiology

The formation and maintenance of a Baker's cysts can occur through a number of mechanisms, including

  1. joint-cyst communication,
  2. sequestration of synovial fluid in the popliteal fossa due to a valve-like effect between the joint space and cyst (controlled by the gastrocnemius-semimembranosus muscle with flexion and extension at the knee),
  3. negative intraarticular knee pressure during partial flexion combined with a positive pressure during extension (as a result directing fluid flow towards the cyst from the suprapatellar bursa during flexion);
  4. gastrocnemius-semimembranosus bursa enlargement resulting from small traumas to the bursa with muscle contractions; and
  5. herniation of the joint capsule into the popliteal fossa.

Histopathology

Histologically, the cyst walls resemble synovial tissue with varying degrees of fibrotic tissue present.  In addition, there may be chronic, nonspecific inflammatory cells present. 

History and Physical

The presence of a Baker’s Cyst may be associated with a sensation of tightness, discomfort, or pain behind the knee. Swelling may be more evident when the patient is standing with full extension at the knee.  Swelling tends to be reduced or disappear as the knee is flexed to 45 degrees (Foucher's sign occurs due to the relief of tension on the cyst).  Pain often worsens with increased activity and may inhibit full flexion or extension at the knee. 

As a Baker's Cyst enlarges, it may compress surrounding vessels, resulting in lower extremity edema as a result of venous obstruction. If the cyst begins to enlarge into the calf muscle (i.e., dissecting cyst), this too can result in swelling, erythema, distal edema, and a positive Homan's sign - similar to what one might expect to see in a patient presenting with thrombophlebitis or a deep vein thrombosis (DVT).

A Baker’s Cyst may rupture if, due to rapid accumulation of fluid, pressure within the sac becomes too high. When the fluid is released into the surrounding tissues, it may result in inflammation that may then elicit symptoms similar to those that would be experienced with thrombophlebitis in the calf. Symptoms may include sharp pain in the knee and calf, swelling or erythema of the calf, and a sensation that feels like water running down the calf. In addition, thrombophlebitis rarely can result as a complication of a bulging or ruptured Baker’s Cyst.

Cyst rupture also may lead to additional complications and associated symptoms. These can include (1) entrapment of the posterior tibial nerve (eg., posterior plantar numbness and calf pain), (2) occlusion of the popliteal artery (e.g., lower extremity edema), and (3) anterior (e.g. foot drop and edema of the anterolateral leg) or posterior (e.g. plantar dysesthesia, weakness of toes, swelling of the calf, and pain worse with passive toe extension) compartment syndrome. 

Evaluation

A Baker's Cyst typically is diagnosed by having the patient stand and extend the knee full; this is when the mass should be most prominent. When the knee is flexed to 45 degrees, the mass often either softens or fully disappears (e.g., Foucher's sign) due to the relief of tension within the cyst. The patient also should be examined in a supine position, where the knee is passively moved from full extension to at least 90 degrees flexion, to ensure adequate examination of the knee joint. 

If a Baker's Cyst is located more laterally or no changes are elicited in the cyst when the knee is examined in a full range of motion, it may be difficult to conclude a diagnosis of Baker's Cyst through physical examination alone, especially in a setting of no prior history of knee pathology.[6][7][8]

If this is the case, and a diagnosis of Baker's Cyst remains uncertain, imaging should be performed. This includes plain radiography and ultrasonography, followed by MRI, especially if considering surgery.

Treatment / Management

Treatment is not usually necessary for a Baker's Cyst unless the patient is symptomatic.[8][9][10]  Incidental findings in the asymptomatic patient are managed with observation and reassurance alone.

Non-operative management:

  • Rest/activity modification
  • NSAIDs
  • PT/rehab regimens are often effective in patients with minimal symptoms, and in the setting of smaller degenerative meniscal tears
  • Aspiration and steroid injection
    • The knee joint itself can be treated with a cortisone injection in the setting of moderate to advanced tricompartmental degenerative knee arthritic conditions.  This can help manage patients' symptoms and clinically differentiate the contribution of the popliteal cyst itself on the patients daily symptoms
    • Ultrasound-guided aspiration and injection can be performed by an experienced interventional radiologist
      • Recurrence rates are much lower in younger patient populations
      • Recurrence rates are higher in older patient populations and degenerative meniscal tears with associated cysts

Operative management

  • Arthroscopic debridement, cyst decompression, meniscal repair vs partial meniscectomy
    • less invasive than the open approach
    • often results in cyst recurrence, especially in older patients with moderate-advanced knee degenerative conditions
  • Open cyst excision
    • Posterior approach to the knee is utilized
    • Not indicated in the setting of underlying knee degenerative conditions secondary to the risk of cyst recurrence

It is important to treat the underlying joint disorder, if one exists, in all patients with symptomatic Baker's cysts. This will help reduce the accumulation of synovial fluid and enlargement of the cyst.

Pearls and Other Issues

It is important to rule out other possible disorders that may mimic many of the key clinical features of a Baker's cyst. These include deep vein thrombosis (DVT), cystic masses (e.g., synovial or ganglion cysts), solid masses, (e.g. sarcomas and lymphoma), and popliteal artery aneurysms. Given the potential complication of pseudothrombophlebitis (e.g., swelling, warmth, tenderness, and a positive Homan's sign) caused by a Baker's cyst when markedly enlarged, dissected, or ruptured), it is especially important to distinguish this finding from a true DVT that may present with similar symptoms.

Enhancing Healthcare Team Outcomes

Baker cyst is often seen by the primary care provider, internist and nurse practitioner. It is important to get an ultrasound to ensure that there is no other pathology. If the patient is symptomatic, he or she should be referred to an orthopedic surgeon. The majority of patients require no treatment. Various treatments do exist for symptomatic patients but with all of them, recurrence is a possibility. The outcomes are good in most patients as the disorder is benign.[11][12] (Level V)


  • Image 9765 Not availableImage 9765 Not available
    Image courtesy S Bhimji MD
Attributed To: Image courtesy S Bhimji MD

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Baker's Cyst - Questions

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With a Baker cyst in the popliteal fossa, you would expect what condition?



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What is the most common mass found in the popliteal fossa?



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When excising a Baker cyst, what nerve is most likely to be injured?



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Where is a Baker cyst found?



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A patient presents with pain and difficulty with knee extension and a fluctuating mass behind the knee. What is the most likely diagnosis?



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Baker cysts are associated with:



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A painful swelling in the popliteal fossa in a patient with rheumatoid arthritis is most likely:



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Baker's Cyst - References

References

Hyland S,Varacallo M, Anatomy, Bony Pelvis and Lower Limb, Popliteal Region 2019 Jan;     [PubMed]
Tofte JN,Holte AJ,Noiseux N, Popliteal (Baker's) Cysts in the Setting of Primary Knee Arthroplasty. The Iowa orthopaedic journal. 2017;     [PubMed]
Jacobson JA,Ruangchaijatuporn T,Khoury V,Magerkurth O, Ultrasound of the Knee: Common Pathology Excluding Extensor Mechanism. Seminars in musculoskeletal radiology. 2017 Apr;     [PubMed]
Shah A,James SL,Davies AM,Botchu R, A diagnostic approach to popliteal fossa masses. Clinical radiology. 2017 Apr;     [PubMed]
Picerno V,Filippou G,Bertoldi I,Adinolfi A,Di Sabatino V,Galeazzi M,Frediani B, Prevalence of Baker's cyst in patients with knee pain: an ultrasonographic study. Reumatismo. 2014 Mar 14;     [PubMed]
Leow KS,Chew KM,Chawla A,Lim TC, Sonographic assessment of musculoskeletal causes of calf pain and swelling. Emergency radiology. 2019 Feb 13;     [PubMed]
Tejero S,T Fenero-Delgado B,López-Lobato R,Carranza-Bencano A, Ruptured Baker's cyst: complications due to misdiagnosis. Emergencias : revista de la Sociedad Espanola de Medicina de Emergencias. 2018 Dic;     [PubMed]
Fels Elliott DR,Ljung BM,Patel R,Iezza G, Primary diagnosis of ruptured biceps tendon     [PubMed]
Lueders DR,Smith J,Sellon JL, Ultrasound-Guided Knee Procedures. Physical medicine and rehabilitation clinics of North America. 2016 Aug;     [PubMed]
Martel Villagrán J,Bueno Horcajadas Á,Agrela Rojas E, Musculoskeletal interventional radiology: ultrasound and CT. Radiologia. 2016 May;     [PubMed]
Xinxian X,Yuezheng H,Jian L,Huachen Y, Clinical outcome of arthroscopic management of popliteal cysts with or without additional posterior open cystectomy. Der Orthopade. 2018 Jun;     [PubMed]
Yang B,Wang F,Lou Y,Li J,Sun L,Gao L,Liu F, A comparison of clinical efficacy between different surgical approaches for popliteal cyst. Journal of orthopaedic surgery and research. 2017 Oct 25;     [PubMed]

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