A Baker’s cyst (or popliteal cyst) is a fluid-filled cyst that develops behind the knee and is usually a sign of another condition.
Anatomy & Pathology
Baker’s cysts develop posterior to the knee joint and are usually found directly behind the medial femoral condyle between the medial head of the gastrocnemius muscle and the semimembranosus tendon. The cyst forms from an existing bursa in this area; specifically the gastrocnemius-semimembranosus bursa, also called the popliteal bursa. This bursa is connected to the knee’s joint capsule. This connection between the popliteal bursa and joint capsule allows the cyst to develop.
The cyst develops because there is not a free exchange of fluid between the popliteal bursa and the internal knee structures. The connection between the bursa and joint capsule creates a one-way valve that only lets fluid pass from the internal knee joint back to the bursa. As a result, fluid cannot move back into the capsule, which consequently collects in the bursa, causing it to enlarge.
Because the cyst’s lining is intimately connected with the joint capsule of the knee, irritation of the capsular tissues may have something to do with the excess inflammatory reaction.
Baker’s cysts are the most common cysts found around the knee and are usually associated with degenerative or trauma-induced knee pathologies, such as osteoarthritis, rheumatoid arthritis, meniscal tears, ligament tears, or osteochondritis dissecans
Symptoms & Testing
Clients with Baker’s cyst may be asymptomatic until the inflammation restricts pain-free movement. Common symptoms include a sense of tightness behind the knee, pain or discomfort, and can prevent full knee flexion and full extension. Notably, symptoms can be increased during both flexion and extension movements. Flexion movements compress the cyst, while extension movements can pull on the inflamed cyst, causing more pain. Cysts are visible when the client stands and are also palpable.
Doing a proper assessment, particularly palpation, in cases of knee injury or degenerative conditions could reveal a Baker’s cyst. In these cases, a massage therapist can help catch this problem and refer the client to an orthopedist.
As fluid develops within the cyst, it can press on other structures, particularly blood vessels, impeding blood flow and causing swelling. If the cyst continues to grow into the calf, the symptoms can mimic thrombophlebitis or deep vein thrombosis (DVT).
Extreme complications associated with cyst rupture include nerve entrapment or vascular compression. These problems may produce calf swelling, muscle weakness, loss of sensation, and pain.
Because Baker’s cysts result from other pathologies, it is essential to address those other problems. If the original problem can be resolved, the Baker’s cyst will resolve on its own. Treatment requires stopping activities that cause pain or exacerbate the swelling. Clients should avoid activities requiring a lot of knee bending, such as squats, lunges, cycling, climbing, or kneeling. Avoiding cyst rupture is particularly important.
Baker’s cysts are aspirated usually with guided ultrasound, and corticoid steroid injections may be used. There may be cases in which the thickness of the cyst fluid prevents aspiration. Surgical removal is a last resort.
The back of the knee is an endangerment site, so practitioners should be cautious about pressure in this region as it can damage neurovascular tissues. Because Baker’s cysts are fluid-filled masses with a one-way valve, mechanical pressure on the cyst will not aid fluid movement and could worsen the problem. Putting further pressure on a Baker’s cyst could occur when attempting to treat one of these deeper knee muscles. In general, massage is avoided.