Baker’s cyst (Popliteal cyst)

BASIC INFORMATION
In approximately 5% of patients with a knee effusion, a swollen, painful popliteal cyst develops. This is usually due to a bursa (usually the semimembranosus bursa), which in some individuals has a valve-like connection to the knee. This allows the effusion to flow into the bursa but not back. Occasionally there is a synovial herniation through the posterior joint capsule. The cyst is best seen and felt in the popliteal fossa with the patient standing.

Ruptured popliteal cyst.

A popliteal cyst may rupture if the patient is mobile, particularly on standing up quickly or climbing stairs. Fluid escapes into the soft tissue of the popliteal fossa and upper calf, causing sudden and severe pain, swelling and tenderness of the upper calf. Dependent oedema of the ankle develops and the knee effusion reduces dramatically in size and may be undetectable.
A history of previous knee problems and the sudden onset of pain and tenderness high in the calf suggest a ruptured cyst rather than a deep vein thrombosis (DVT). However, the diagnosis is often missed and treated inappropriately with anticoagulants. A diagnostic ultrasound examination distinguishes a ruptured cyst from a DVT. Analgesics or NSAIDs, rest with the leg elevated, and aspiration and injection with corticosteroids into the knee joint are required.

Baker popliteal cyst knee aspiration

Baker's Cyst

EPIDEMIOLOGY & DEMOGRAPHICS
* Popliteal cysts occur at all ages.
* Incidence of Baker’s cysts is unknown.
* Between 3% to 7% of all patients thought to have clinical deep vein thrombosis turn out to have symptomatic Baker’s cysts.
* Approximately 6-8% of MRIs of the knees reveal popliteal cysts.
PHYSICAL FINDINGS & CLINICAL PRESENTATION
* Pain in the popliteal space;
* Knee swelling;
* Leg edema;
* Prominence of the popliteal fossa;
* Decreased range of motion of the knee;
* Locking of the knee;
* Foucher’s sign: The cyst becomes hard with knee extension and soft with knee flexion;
* Neuropathic lancinating pains radiating from the knee down the back of the leg;
* Deep vein thrombosis (DVT).
ETIOLOGY
* Baker’s cysts are believed to represent fluid distention of the bursal sac separating the semimembranous tendon from the medial head of the gastrocnemius.
* In children, Baker’s cysts are thought to be secondary to trauma and irritation of the knee.
* In adults, Baker’s cysts are usually associated with pathologic changes of the knee joint:
a). Rheumatoid arthritis;
b). Osteoarthritis of the knee;
c). Meniscal tears;
d). Patellofemoral chondromalacia;
e). Fracture;
f). Gout;
g). Pseudogout;
h). Infection (tuberculosis).
DIAGNOSIS
Baker’s cysts, like deep vein thrombosis, are very difficult to diagnose on clinical grounds alone. In fact, Baker’s cyst frequently mimics a deep vein thrombosis and is sometimes called pseudothrombophlebitis syndrome.
DIFFERENTIAL DIAGNOSIS
* Deep vein thrombosis;
* Popliteal aneurysms;
* Abscess;
* Tumors;
* Lymphadenopathy;
* Varicosities;
* Ganglion;

WORKUP
Anyone suspected of having a popliteal cyst should undergo imaging studies to exclude other causes.
LABORATORY TESTS
Blood tests are not very specific in the diagnosis of Baker’s cysts.
IMAGING STUDIES
* Plain x-ray (AP and lateral views) may show calcification in a solid tumor or in the posterior meniscal area.
* Ultrasound is easy, cost effective, and excludes other causes of popliteal fossa pathology.
* MRI of the knee identifies coexisting joint pathology (for example, osteoarthritis, torn meniscus).
* Noninvasive venous studies to rule out deep vein thrombosis.
TREATMENT
Treatment is directed at the underlying pathology leading to the formation of the popliteal cyst.
NONPHARMACOLOGIC THERAPY
* Rest
* Strenuous activity avoidance
* Knee immobilization possibly necessary in some cases
ACUTE GENERAL Rx
* NSAIDs, ibuprofen 400 to 800 mg PO tid, or naproxen 250 to 500 mg. PO bid can be used to treat Baker’s cyst caused by RA, gout, and pseudogout.
* Intraarticular injection or injection of the cyst with corticosteroids, triamcinolone acetonide 40 mg. is sometimes tried.
CHRONIC Rx
* Surgical procedures addressing the underlying cause or aimed at the cyst include:
a). Arthroscopic surgery to remove loose cartilaginous fragment
b). Partial or total meniscectomy
c). Open excision of the cyst
DISPOSITION
* Baker’s cyst may spontaneously resolve without treatment.
* Complications of Popliteal cyst are:
a). Rupture
b). Deep vein thrombosis
c). Nerve impingement