Baker’s cyst at a glance

What is a Baker’s cyst?

A Baker’s cyst, also called a popliteal cyst, is a collection of synovial fluid behind the knee. Synovial fluid normally helps the knee joint move smoothly.

When the joint becomes irritated, it may produce more fluid than usual. Some of this fluid can move through a valve-like opening and collect in a small sac behind the knee.

The cyst may feel soft or firm. Its size can also change over days or weeks, depending on activity and the amount of swelling inside the joint.

For a broader overview of knee symptoms and possible causes, see our guide to knee pain and injury.

Why does a Baker’s cyst form?

In adults, a Baker’s cyst usually reflects another problem inside the knee rather than being a separate condition.

Children can also develop Baker’s cysts. However, the causes and usual progression may differ from those seen in adults.

What are the symptoms of a Baker’s cyst?

Some Baker’s cysts cause no symptoms. Others become noticeable during activity or when the knee is fully bent or straightened.

• A visible or palpable lump behind the knee
• Tightness or pressure in the back of the knee
• Aching after walking, standing, stairs or sport
• Stiffness when bending or straightening the knee
• Reduced knee flexion, particularly during squats or kneeling
• General knee swelling related to the underlying joint problem

The size of the cyst does not always match the level of discomfort. A small cyst may feel irritating, while a larger cyst may cause few symptoms.

Could the lump be something else?

Not every lump behind the knee is a Baker’s cyst. Other causes of posterior knee swelling or discomfort may include muscle or tendon problems, vascular conditions, another type of cyst or a soft-tissue mass.

Arrange an assessment when a lump is new, enlarging, painful, firm, associated with unexplained symptoms or has not been examined previously.

A clinician may recommend ultrasound or MRI when the diagnosis remains unclear or when symptoms suggest another knee condition.

How is a Baker’s cyst assessed?

A physiotherapy assessment considers both the swelling behind the knee and the reason the knee may be producing extra fluid.

1. Discuss your symptoms

   Your physiotherapist will ask when the swelling began, what aggravates it and whether the knee locks, gives way or repeatedly swells.

2. Examine the knee

   The examination may include knee movement, swelling, joint tenderness and the location and behaviour of the lump.

3. Check strength and movement

   Your physiotherapist may assess walking, stairs, squatting and the strength of the thigh, hip and calf muscles.

4. Decide whether imaging or medical review is needed

   Ultrasound or MRI may help confirm the cyst, examine the knee joint or exclude another cause of swelling.

How is a Baker’s cyst treated?

Treatment depends on your symptoms and the condition affecting the knee. A cyst that causes no pain or restriction may not need direct treatment.

How may physiotherapy help?

Physiotherapy does not directly drain or remove a Baker’s cyst. Instead, treatment aims to improve knee function and address factors that may be contributing to joint irritation.

Restore comfortable movement

Gentle mobility exercises may reduce stiffness and improve bending and straightening. Exercise selection should match the irritability of the knee.

Build strength and capacity

Strengthening may target the quadriceps, hamstrings, calves and hip muscles. Better strength can improve control during walking, stairs, squats and sport.

Manage activity loads

Your physiotherapist can help adjust aggravating activities without unnecessarily stopping all movement. Loads can then increase as symptoms settle.

Plan a gradual return to activity

Rehabilitation should reflect your goals, whether they involve walking, work, gym exercise, running or sport. Our exercise programs and sports injury physiotherapy services may support this process.

Can a Baker’s cyst go away?

A Baker’s cyst may reduce when knee irritation settles and the joint produces less fluid. However, the swelling may return if arthritis, a meniscus problem or another source of inflammation remains active.

Progress varies between people. Some cysts remain present but cause little trouble. Others fluctuate with activity and knee swelling.

Surgery is not usually the first option. Medical or surgical review may be appropriate when symptoms remain severe, the diagnosis is uncertain or significant knee pathology requires further treatment.

What can you do during a flare-up?

• Reduce or modify activities that markedly increase pressure behind the knee.
• Keep the knee moving gently within a comfortable range.
• Avoid forcing deep knee bends when swelling blocks movement.
• Use compression only when it feels comfortable and is suitable for you.
• Return to normal activity gradually rather than testing the knee repeatedly.
• Arrange assessment if swelling persists, recurs or limits your usual activities.

Seek professional advice before starting a new exercise program when the knee is acutely swollen, the diagnosis is uncertain or you have significant medical conditions.

What should you do next?

Arrange an assessment if you have a new lump behind the knee, recurring swelling, restricted movement or symptoms that interfere with walking, work or sport.

A physiotherapist can assess the knee, identify likely contributors and guide a treatment plan that matches your symptoms and goals.

References

1. Healthdirect Australia. Baker’s cysts.
2. Abate M, Di Carlo L, Di Iorio A, Salini V. Baker’s cyst with knee osteoarthritis: clinical and therapeutic implications. Medical Principles and Practice. 2021;30(6):585–591.
3. Malinowski K, et al. Arthroscopic cystectomy and valve excision of popliteal cysts complemented with management of intra-articular pathologies: low recurrence and good functional outcomes. International Orthopaedics. 2023.
4. Irismetov ME, et al. Diagnostics and surgical treatment of ruptured Baker’s cysts. 2024.
5. Hasan M, Berkovich Y, et al. Comprehensive analysis of knee cysts: diagnosis and treatment. 2025.

Baker’s cyst FAQs