The soft lump behind your knee might be a fluid-filled cyst
In short: A Baker's cyst is one of the most common knee disorders, often appearing as a soft lump in the popliteal fossa. While it can cause stiffness and aching, it is rarely a standalone issue; it is usually a secondary signal that your knee joint is struggling with underlying wear and tear.
A Baker's cyst, also known as a popliteal cyst, develops at the back of the knee due to the enlargement of the gastrocnemius-semimembranosus bursa. This bursa is a small fluid-filled sac located between the gastrocnemius and semimembranosus muscles. When the knee joint experiences issues like osteoarthritis or a meniscal tear, the joint produces excess fluid, which then accumulates in this bursa, causing the cyst to swell. Symptoms vary significantly. For many, the cyst is asymptomatic, but it can manifest as a soft lump that becomes more visible when standing. Other common sensations include knee or leg tightness, aching, stiffness, or a clicking sound in the joint. The cyst is a common disorder found in adults. It specifically forms in the popliteal fossa. The fluid-filled lump is often more noticeable when a person stands up. These issues can impact a person's overall mobility.
These symptoms often intensify after walking. If a cyst ruptures, the resulting pain and swelling can persist for several weeks as the body reacts to the fluid release. Diagnosis and treatment focus on the root cause rather than just the cyst itself. Because the cyst is a symptom of joint degeneration, treating the underlying arthritis or cartilage tear typically provides the most effective relief. While some cysts, particularly in children, may resolve on their own, others may require interventions such as painkillers, hydrocortisone injections, physiotherapy, or fluid drainage. Surgery to remove the cyst is rare and usually reserved for repairing significant damage to the knee joint.
Note: Recovery from a cyst might span from several months up to several years.
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Sources
- Summary by Intellect · source: Baker's Cyst Knee - posterior knee swelling and pain
- Also: Baker's cyst
- Also: Baker cyst - Symptoms and causes
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