What Is Popliteal Cyst?
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Popliteal Cyst - Causes, Diagnosis, and Treatment

Published on Feb 28, 2023   -  5 min read


Popliteal cysts, or Baker's cysts, are one of the most commonly occurring disorders in the knee causing pain or discomfort.


Popliteal synovial cysts are frequently found with intra-articular knee disorders such as osteoarthritis (wear and tear arthritis due to loss of cartilage between bones) and meniscus tears (tear in the rubbery cartilage between your thigh and knee bones that acts as a shock absorber). These fluid-filled cysts form a lump at the back of the knee, causing discomfort and stiffness.

Baker's cyst is an eponym named after the British surgeon William Morant Baker, who described eight popliteal cysts he had encountered. He wrote a description of these cases and the treatment he performed. His treatment modalities were above-knee amputation, aspiration, etc., contrasting with the modern-day treatment of this condition.

What Does the Knee Joint Look Like?

Your knee joint is the body's biggest and strongest joint. It comprises the lower end of your thigh bone, the upper end of your shinbone, and the kneecap. The ends of these bones are lined with a smooth layer of articular cartilage preventing direct bone-to-bone contact. The synovial fluid is a clear fluid that fills the joint space, acting as a lubricant to reduce friction. The bursa comprises small fluid-filled sacs that cushion the knee and also contribute to reducing the friction between muscles and surrounding structures.

Who Is Most Prone to Develop Popliteal Cysts?

The most frequent cases of Baker's cysts in adults are those with a history of trauma (such as cartilage or meniscus tears, injury to the knee), in individuals with degenerative/co-existing knee joint disease (such as osteoarthritis, rheumatoid arthritis, infectious arthritis, pigmented villonodular synovitis, meniscal tears).

In children, popliteal cysts arise from a herniated posterior knee joint synovium/capsule and present as a primary condition, unlike in adults.

What Causes This Cyst to Form?

One of the most often observed relationships is cyst formation secondary to degenerative meniscal tears. Popliteal cyst development is also known to be triggered by inflammatory diseases and arthritides. The meniscus acts as a one-way valve. The extruded synovial fluid localizes and consolidates to create a viscous, gel-like substance when the cyst develops in the presence of a meniscal tear.

Baker's cysts can form and persist through a variety of mechanisms, including:

  • Joint-Cyst Communication

  • A valve-like effect between the joint space and cyst causes the sequestration of synovial fluid in the popliteal fossa (controlled by the gastrocnemius-semimembranosus muscle with flexion and extension at the knee)

  • The joint capsule pushes through into the popliteal fossa.

What Are the Symptoms?

A popliteal cyst could range from no symptoms to discomfort, pain, or feeling of fullness at the back of the knee. In addition, you may experience stiffness in your knee joint, sometimes limiting movement. A swelling in your knee joint and leg can also occur. Baker's cyst is an incidental finding on routine examination or scans for an unrelated condition in asymptomatic cases.

How Is the Condition Diagnosed?

You need to provide a complete medical history, a history of injury to the knee, and a description of your symptoms to your doctor. The doctor's physical examination may reveal swelling, joint instability, limited range of motion due to stiffness, a clicking sound when you bend your knee, etc. Imaging tests for Baker's cyst include:

  • X-rays: Though a cyst is not visible on an X-ray, it is prescribed to assess loss of joint space and other signs of arthritis.

  • An ultrasound scan helps visualize the cyst and tells the doctor if it is solid or fluid filled.

  • Magnetic resonance imaging (MRI) scan provides a clear picture of soft tissues and is used to identify fluid-filled space and meniscus tears. It helps distinguish a Baker's cyst from other conditions.

The cyst walls are histologically similar to synovial tissue, with varying degrees of fibrotic tissue present. Furthermore, chronic, nonspecific inflammatory cells may be present.

What Are the Complications?

  • Increased activity frequently worsens the pain and can prevent the knee from fully extending or flexing.

  • A Baker's cyst may compress nearby blood vessels, causing venous blockage and lower extremity edema. Similar to what one might anticipate in a patient presenting with thrombophlebitis of deep vein thrombosis, if the cyst starts to dissect into the calf muscle, this can also cause swelling, erythema, distal edema, and a positive Homan's sign (deep vein thrombosis).

  • If there is an excessive buildup of fluid and pressure inside the sac, Baker's Cyst may burst. When the fluid is expelled, it may cause inflammation in the tissues nearby, which could cause symptoms resembling thrombophlebitis in the calf. Sharp pain in the knee and calf, edema or erythema, and a feeling of water trickling down the calf are possible symptoms.

How Is It Treated?

Baker's cysts typically do not require treatment unless the patient exhibits symptoms. Observation and assurance are sufficient for incidental findings in an asymptomatic patient.

  • Non-surgical (conservative) treatment: In the case of smaller degenerative meniscal tears and patients with few symptoms, physiotherapy/rehab programs are frequently beneficial.

  • Modification of physical activities: Your doctor will advise you to avoid strenuous activities that have a high impact on the knee, such as aerobics, jogging, etc.

  • Non-Steroidal Anti-inflammatory drugs (NSAIDs) may be prescribed to manage pain and swelling.

  • Steroid injection into the joint to reduce inflammation.

  • Aspiration is guided by ultrasound to drain excess fluid from the joint.

  • Surgical treatment: Less intrusive than the open technique, arthroscopic debridement, cyst decompression, and partial meniscectomy frequently result in cyst recurrence, especially in older patients with moderate-advanced knee degenerative diseases.

  • Open cyst removal: The knee is approached from behind. It is not advised because of the possibility of a cyst recurrence in the presence of underlying degenerative knee problems. In all individuals with symptomatic Baker's cysts, the underlying joint problem, if present, must be treated. This will lessen the buildup of synovial fluid and the cyst's expansion.

  • Recent Advancements

    • In particular, the cyst's opening and the cyst, which possesses a valvular mechanism, can now be efficiently treated using recent arthroscopy techniques. Resecting the cyst's inner wall and septa while rectifying the valvular mechanism had outstanding results. Without any intra- or postoperative problems, an arthroscopic technique without cystectomy likewise yielded good clinical results.

    • Primary care physicians, internists, and nurse practitioners frequently treat patients with Baker cysts. To be sure there are no other pathologies, it is crucial to undergo an ultrasound. If the patient exhibits symptoms, an orthopedic surgeon should be consulted. Most patients don't need to be treated. Many treatments are available for symptomatic people, but recurrence is always a risk. Since the illness is benign, the majority of patients have positive results.

What Steps Are Followed for Post-surgical Recovery?

It is critical to follow your recovery instructions to avoid a recurrence of a Baker's cyst.

  • Early Motion: If your cyst was aspirated or you had arthroscopic surgery, you should be able to walk immediately after the procedure. However, you should avoid strenuous activity during your recovery.

  • Bracing: Your doctor may advise you to wear a knee brace for several weeks following surgery to immobilize your knee.

  • Therapy for the Body: Specific exercises can help you improve your range of motion and strengthen the muscles around your knee.

The amount of time it takes to recover from surgery varies depending on whether the underlying condition in the joint was treated during the procedure.


Baker’s cyst is a common condition presenting as a lump or swelling behind the knee. It is formed due to an underlying problem or can be idiopathic. Most cases do not require treatment.

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28 Feb 2023  -  5 min read




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