Baker’s Cyst

• Johannes Steiner, M.D.
• Richard Regnante, M.D.

 Basic Information

Definition

Baker’s cyst is a fluid-filled popliteal bursa located along the medial border of the popliteal fossa. It is an extension of the semimembranosus bursa posteriorly (see Fig. E1).

Synonyms

1. Popliteal synovial cyst

ICD-10CM CODES
M71.2	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

Epidemiology & Demographics

1. Most are asymptomatic and incidentally found on imaging exams.

2. Occurs at all ages, most commonly between age 35 to 70 yr, increasing with age.

3. The prevalence of popliteal cysts varies based on the imaging technique used and the age of the patient population.

4. Between 2% and 6% of all patients believed to have clinical deep venous thrombosis (DVT) have symptomatic Baker’s cysts.

5. Approximately 5% to 40% of MRIs performed for osteoarthritis or internal derangement reveal popliteal cysts.

Physical Findings & Clinical Presentation

1. Symptoms associated with associated joint pathology (knee swelling or stiffness)

2. Pain in the popliteal space

3. Leg edema

4. Prominence of the popliteal fossa

5. Decreased range of motion of the knee

6. Locking of the knee

7. Foucher’s sign: the cyst becomes hard with knee extension and soft with knee flexion.

8. Neuropathic lancinating pains radiating from the knee down the back of the leg

9. Pain or discomfort with prolonged standing and hyperflexion of the knee

10. Presence of associated DVT

Etiology

1. Believed to be fluid distention of bursal sac separating semimembranous tendon from medial head of gastrocnemius.

2. May represent a true cyst but more often a degenerative or inflammatory joint disease or injury; they usually communicate with adjacent knee joint space. Thus, a Baker’s cyst usually denotes increased intraarticular pressure from underlying joint disease. Sequestration of synovial fluid in the popliteal fossa can result from a valve-like effect between joint space and cyst controlled by gastrocnemius-semimembranosus muscle changes with knee flexion and extension.

3. In children, popliteal cysts are usually a primary process arising from the gastrocnemius-semimembranosus bursa without direct communication with the joint space.

4. In adults, Baker’s cysts are usually associated with pathologic changes of the knee joint, such as the following:

   1. Rheumatoid arthritis (RA)

   2. Osteoarthritis of the knee

   3. Meniscal tears

   4. Patellofemoral chondromalacia

   5. Fracture

   6. Gout

   7. Pseudogout

   8. Infection (tuberculosis)

Diagnosis

Baker’s cyst frequently mimics DVT and is sometimes referred to as pseudothrombophlebitis syndrome.

Differential Diagnosis

1. DVT

2. Popliteal artery aneurysm

3. Abscess

4. Tumor (sarcomas/lymphomas)

5. Lymphadenopathy

6. Varicosity

7. Synovial or ganglion cysts

Workup

The diagnosis can be made by physical examination alone. However, anyone suspected of having a popliteal cyst should undergo imaging studies to exclude other causes.

Laboratory Tests

Blood tests are not specific.

Imaging Studies

1. Plain radiographs (AP and lateral views) may show calcification in a solid tumor or in the posterior meniscal area.

2. Ultrasound (Fig. E2) is safe, portable, and cost effective and excludes other clinically important causes of popliteal fossa pathology, including DVT.

   

3. MRI if internal derangement is suspected, surgery being considered, or diagnosis unclear after ultrasound.

Treatment

Asymptomatic cysts found incidentally do not require treatment.

Nonpharmacologic Therapy

1. Rest

2. Strenuous activity avoidance

3. Knee immobilization sometimes necessary

Acute General Rx

1. NSAIDs can be used to treat underlying joint pathology (RA, gout, and pseudogout).

2. Arthrocentesis with intraarticular injection or injection of the cyst with corticosteroids (triamcinolone acetonide 40 mg).

Chronic Rx

1. The majority of Baker’s cysts are successfully treated conservatively.

2. If refractory symptoms, surgical procedures addressing the underlying cause include:

   1. Arthroscopic surgery to remove loose cartilaginous fragment

   2. Partial or total meniscectomy

   3. Open excision of the cyst

Disposition

1. Baker’s cyst may spontaneously resolve without treatment.

2. Complications of Baker’s cysts include:

   1. Rupture

   2. DVT

   3. Nerve impingement resulting in posterior tibial nerve entrapment, anterior compartment syndrome, or posterior compartment syndrome

   4. Popliteal artery occlusion

Referral

Orthopedic surgeon if surgery is contemplated

Related Content

Baker’s Cyst (Patient Information)