Fluid-Filled Lump Behind the Knee – Causes, Diagnosis and Treatment

Fluid-Filled Lump Behind the Knee – Causes, Diagnosis and Treatment at Emirates Hospitals Group 

Overview

A fluid-filled lump behind the knee, commonly known as a Baker’s cyst (or popliteal cyst), is a swelling that occurs when fluid accumulates in the popliteal bursa, a small sac of fluid located behind the knee joint. While it is typically harmless and may not cause symptoms, a large cyst can cause discomfort, pain, and limited movement.

Causes

1. Knee Joint Conditions – The most common cause of a Baker’s cyst is underlying knee joint problems, such as arthritis, osteoarthritis, or rheumatoid arthritis. These conditions increase fluid production in the knee, which can then accumulate in the bursa.
2. Knee Injury – Injuries such as meniscus tears or ligament injuries can lead to inflammation or fluid buildup in the knee joint, contributing to cyst formation.
3. Overuse – Repetitive motion or overuse of the knee joint can irritate the tissues and result in fluid retention.
4. Infection – In rare cases, an infection in the knee joint can cause fluid to accumulate in the bursa, forming a cyst.
5. Tumors – While less common, tumors or growths in the area may also lead to the development of a fluid-filled lump.

Diagnosis

1. Physical Exam – A doctor will check for swelling and tenderness in the back of the knee, as well as assess knee movement and range of motion.
2. Imaging – An ultrasound or MRI scan can confirm the presence of a cyst, measure its size, and check for underlying causes such as joint problems or tears.
3. Aspiration – In some cases, a doctor may use a needle to withdraw fluid from the cyst and analyze it for signs of infection or other conditions.

Treatment Options

• Conservative Care – Many small Baker’s cysts resolve on their own with rest, ice, and over-the-counter pain relievers.
• Drainage – If the cyst is large or painful, the fluid may be drained using a needle, though the cyst may return.
• Corticosteroid Injections – Injecting steroids into the knee joint may help reduce inflammation and prevent further fluid buildup.
• Surgery – If the cyst persists or is associated with significant knee joint damage, surgical removal may be necessary.

If you notice a fluid-filled lump behind the knee, it is advisable to consult a healthcare provider for proper diagnosis and management.

Related Treatments

• Baker’s Cyst