Article by Dr Manasa S, B.A.M.S
A Baker’s cyst, also known as a popliteal cyst or synovial cyst, is a small, fluid-filled bump that forms on the back of the knee. This condition arises when damage to the knee joint or surrounding tissues causes excess fluid to drain out of the knee. Since the fluid can only exit in one direction, it accumulates at the back of the joint, forming the sac that becomes a Baker’s cyst. While these cysts may cause discomfort or restrict movement, they are benign growths, meaning they are non-cancerous and do not indicate or lead to cancer.
Causes of Baker’s Cyst
Baker’s cysts, or popliteal cysts, form due to the accumulation of excess synovial fluid in the popliteal bursa, a fluid-filled sac located at the back of the knee. This condition arises from various underlying causes that lead to inflammation or overproduction of synovial fluid.
Mechanism of Fluid Accumulation
The knee joint comprises bones, tendons, and cartilage, all of which require lubrication provided by synovial fluid to facilitate smooth movement and reduce friction. Synovial fluid circulates through several bursae, which are small fluid-filled sacs within the knee. A valve-like system between the knee joint and the popliteal bursa regulates the flow of synovial fluid. When the knee produces an excessive amount of synovial fluid, it can accumulate in the popliteal bursa, leading to the formation of a Baker’s cyst.
Underlying Conditions
Several conditions can cause an overproduction of synovial fluid or inflammation in the knee joint, contributing to the development of a Baker’s cyst:
Osteoarthritis: This common form of arthritis involves the breakdown and eventual loss of cartilage in the joints, leading to inflammation and pain, which can increase synovial fluid production.
Rheumatoid Arthritis: An autoimmune disorder that causes chronic inflammation of the joints, resulting in pain, swelling, and increased synovial fluid.
Gout: A condition where high levels of uric acid in the blood cause urate crystals to accumulate in the joints, leading to severe inflammation and pain.
Lupus: An autoimmune disease where the body’s immune system attacks healthy tissue, causing widespread inflammation, including in the joints.
Haemophilia: A genetic disorder that impairs the blood’s ability to clot, leading to internal bleeding and joint damage, which can result in excess synovial fluid production.
Psoriatic Arthritis: Associated with psoriasis, this condition causes joint pain and inflammation.
Reactive Arthritis: A chronic type of arthritis triggered by an infection in another part of the body, leading to joint inflammation.
Septic Arthritis: Joint inflammation caused by a bacterial infection, leading to increased synovial fluid as the body attempts to fight the infection.
Knee Injuries: Trauma or injuries to the knee, such as cartilage tears, are common among athletes and can lead to the development of a Baker’s cyst due to increased fluid production as the body attempts to heal the injury.
Understanding these causes is essential for diagnosing and managing Baker’s cysts effectively, as treatment often involves addressing the underlying condition to prevent recurrence and alleviate symptoms.
Pathophysiology of Baker’s Cyst
The development and persistence of Baker’s cysts, also known as popliteal cysts, involve several intricate mechanisms:
Joint-Cyst Communication: There is a direct communication between the knee joint and the cyst. This allows synovial fluid to flow into the cyst from the joint space.
Valve-Like Effect: The gastrocnemius and semimembranosus muscles create a valve-like mechanism that affects the flow of synovial fluid. During knee movements, particularly flexion and extension, this effect can trap fluid in the popliteal fossa, contributing to cyst formation and maintenance.
Pressure Dynamics in the Knee:
Negative Intraarticular Pressure: When the knee is partially flexed, negative pressure within the joint can draw fluid towards the cyst.
Positive Pressure During Extension: Conversely, during knee extension, positive pressure within the joint directs fluid into the cyst. This dynamic helps maintain the cyst as fluid continuously flows towards it, particularly from the suprapatellar bursa during flexion.
Bursa Enlargement: The gastrocnemius-semimembranosus bursa can enlarge due to minor traumas from muscle contractions. Repeated small injuries to the bursa can lead to its expansion, contributing to cyst formation.
Joint Capsule Herniation: In some cases, part of the joint capsule may herniate into the popliteal fossa, forming a cystic structure that fills with synovial fluid.
These mechanisms, individually or collectively, result in the formation and persistence of Baker’s cysts.
Symptoms of Baker’s cyst
Common Symptoms
Swelling Behind the Knee: One of the most noticeable symptoms of a Baker’s cyst is swelling located at the back of the knee. The accumulation of excess synovial fluid in the popliteal bursa causes the characteristic swelling. This swelling can vary in size and is often visible as a bulge when the knee is in certain positions. This fluid build up is often due to underlying knee conditions, such as arthritis or a meniscal tear.
Swelling in the Leg: In addition to swelling behind the knee, some patients may experience swelling that extends down the leg. This can be due to the cyst putting pressure on surrounding tissues and veins, leading to fluid accumulation in the lower leg.
Knee Pain: Pain in the knee joint is a common symptom, which can range from a dull ache to sharp, severe pain. Pain arises due to the cyst exerting pressure on surrounding tissues, including nerves and muscles. The pain may worsen with physical activity or prolonged standing and can interfere with daily activities.
Stiffness and Limited Mobility: Baker’s cysts often cause stiffness in the knee, making it difficult to bend or fully extend the leg. This limited range of motion can hinder walking, climbing stairs, and other movements that require knee flexibility.
Risk factors
Anyone can develop Baker’s cyst, if someone has arthritis or has had injury then they are most likely to have Baker’s cyst.
Others who are at risk of developing Baker’s cyst are as under –
– People who are aged 35 to 75 years
– Athletes
– People with arthritis
– People who are used to put lot of pressure on their knees at work or during hobby
Complications
Rupturing of the Baker’s cyst is the most common complication.
The ruptured cyst causes additional symptoms like
– Swelling in the calf and lower leg
– Nerve damage
– A sharp, stabbing type of pain
– A feeling of water running down the leg
– Painful extra pressure in the muscles
Diagnosis and tests
– Physical examination forms the first line in the diagnosis of the cyst
– X-rays
– Ultrasound
– Magnetic resonance imaging [MRI]
Can you prevent a Baker’s cyst?
The best way to prevent a Baker’s cyst is to avoid knee injuries. Here are some tips to help you stay safe during sports and physical activities:
– Wear the right protective equipment: Ensure you have the appropriate gear for the sport or activity you are participating in.
– Listen to your body: Don’t “play through the pain” if your knee hurts during or after physical activity.
– Rest and recovery: Allow your body time to rest and recover after intense activity to prevent overuse injuries.
– Warm up and stretch: Before engaging in sports or workouts, take time to stretch and warm up your muscles.
– Cool down and stretch: After physical activity, cool down and stretch to maintain flexibility and reduce muscle soreness.
Additionally, follow these general safety tips to reduce the risk of injuries:
– Keep areas clutter-free: Ensure your home and workspace are free from clutter that could cause tripping hazards.
– Use proper equipment: Always use the correct tools or equipment to reach high places. Avoid standing on chairs, tables, or countertops.
– Use mobility aids if needed: If you have difficulty walking or are at increased risk of falls, use a cane or walker for added stability.
Treatment and Management of Baker’s Cyst
Non-Operative Management
RICE Method: Most minor injuries can be treated effectively with the RICE method:
– Rest: Stop the activity that caused the injury to prevent further damage.
– Ice: Apply an ice pack or cold compress for 10 to 15 minutes every hour on the first day after the injury. After the first day, apply ice every three to four hours. Always wrap the ice pack in a towel or washcloth to avoid direct contact with the skin.
– Compression: Use a compression bandage or wrap around your knee to reduce blood flow and swelling. Compression pants can also help keep pressure on your knee.
– Elevation: Elevate your knee and lower leg above the level of your heart, if possible. Use pillows, blankets, or cushions for support.
Non-Steroidal Anti-Inflammatory Drugs (NSAIDs): These medications can help reduce inflammation and pain associated with the cyst.
Corticosteroid injection: This helps to reduce inflammation and relieves pain, but there is no guarantee about the risk of recurrence.
Physical Therapy and Rehabilitation: Structured physical therapy regimens can be effective, particularly in patients with minimal symptoms or those with smaller degenerative meniscal tears. Exercises aim to improve knee strength and flexibility, which may help in reducing symptoms.
Aspiration and Steroid Injection:
– Aspiration: Removing the fluid from the cyst with a needle can provide relief.
– Steroid Injection: Injecting corticosteroids into the knee joint can reduce inflammation and help differentiate the cyst’s contribution to the patient’s symptoms, especially in moderate to advanced tricompartmental knee arthritis.
Ultrasound-Guided Procedures: Aspiration and injection performed under ultrasound guidance by an experienced interventional radiologist can be more precise.
Recurrence Rates: These procedures are generally more successful in younger patients, with lower recurrence rates compared to older individuals or those with degenerative meniscal tears.
Operative Management
Arthroscopic Procedures:
– Debridement and Cyst Decompression: Arthroscopy can be less invasive than open surgery and involves cleaning out the joint and decompressing the cyst.
– Meniscal Repair or Partial Meniscectomy: If a meniscal tear is present, it can be repaired or partially removed.
Recurrence: Despite being less invasive, there is a higher chance of cyst recurrence, especially in older patients with advanced knee degeneration.
Open Cyst Excision:
Surgical Approach: This involves a posterior approach to the knee to remove the cyst.
Indications: Open excision is not typically recommended for patients with underlying knee degenerative conditions due to the high risk of recurrence.
Treating the Underlying Condition
For all patients with symptomatic Baker’s cysts, it is crucial to address any underlying joint disorders. Treating conditions such as arthritis or meniscal tears can help reduce the production of synovial fluid, which in turn may prevent the cyst from enlarging and causing further symptoms.
Study – One study showed that an increase in chondral lesion severity increases the amount of effusion and cyst volume.
Study – Another study showed that ultrasound shows excellent diagnostic accuracy for the assessment of Baker’s Cyst and provides similar diagnostic information compared to MRI.
Ayurveda Understanding of Baker’s Cyst
Baker’s Cyst can be correlated with –
Granthi – which means cyst. A granthi, that too Kaphaja type ofo granthi formed at the back of the knee joint can be said to be a Baker’s cyst. When there is more fluid accumulation it can be a kaphaja type. The discharges mentioned in case of kaphaja granthi reflects the explanation of an infected cyst. If the fluid is inflammatory in origin and is caused due to inflammation, it can be a pittaja type. When caused due to injury to the knee joint or structures and tissues around it, it is a vataja type to start with. The other dosha or doshas can get involved in a granthi caused by one dosha in the later stages of pathogenesis.
Shotha – which means swelling. It includes all types of swellings, general or localized (as in Baker’s cyst), inflammatory or non-inflammatory. From the doshic perspective, it follows the same explanation as given in the case of granthi.
The granthi or shotha can also be secondary to other conditions and diseases like amavata, sandhigata vata and vatarakta.
A condition explained in the context of Vata Vyadhi i.e. Kroshtuka Shirsha – wherein a large painful swelling occurs at the centre of the knee joint can also be considered as Baker’s Cyst caused due to vata and rakta.
The treatment principles include dealing with the main dosha or doshas involved in the pathogenesis or treating the condition on the lines of treating granthi or shotha or the primary conditions like amavata etc causing them, as mentioned above.
Related Reading – ‘Baker’s Cyst – Ayurveda Understanding’
