Baker’s Cyst: Symptoms, Treatment and Warning Signs

01Popliteal cyst

What a popliteal cyst is

Mayo Clinic explains that the knee contains a lubricating fluid called synovial fluid, which reduces friction between its moving parts. Some knee conditions make the joint produce too much of this fluid. The excess can build up and move into a bursa, a small fluid-filled sac behind the knee, which swells and forms a cyst.

The NHS describes a Baker’s cyst as a fluid-filled lump at the back of the knee that may get better on its own or by treating the condition causing it. Anyone can get one, but the NHS notes they are more common in people aged 35 to 70.

02Symptoms

Symptoms and variation

Sometimes a Baker’s cyst causes no symptoms at all. When it does, Mayo Clinic and the NHS describe:

• a soft lump or swelling behind the knee, which may be more visible when standing
• knee or leg pain
• tightness, stiffness or aching in the knee, with difficulty fully bending it
• pain when fully straightening or bending the knee
• clicking in the knee

Symptoms may be worse after walking, being active or standing for a long time. Pain behind the knee can also come from muscles or other structures; our guide on a pulled muscle behind the knee covers that.

03Causes

Knee conditions that can increase joint fluid

In adults, a Baker’s cyst usually develops when another condition affects the knee joint. The two sources list:

• inflammation of the knee from arthritis, such as osteoarthritis or rheumatoid arthritis
• gout
• a knee injury, such as a cartilage tear

The NHS notes that sometimes there is no particular cause, especially in children. Our guides on a meniscus tear and knee cartilage damage explain two of the knee problems that can lie behind a cyst.

04New lumps

Why a new lump needs assessment

Although Baker’s cysts are usually harmless, the NHS advises that you should get any lump checked by a GP, and see a GP if you have a lump anywhere on your body and do not know what it is. A lump behind the knee should not be assumed to be a Baker’s cyst until it has been examined.

Do not try to burst, drain or massage the cyst yourself. When draining the fluid is appropriate, the NHS lists it as a treatment carried out by health professionals, and the sources link improvement to treating the knee problem that causes the cyst.

06Assessment

Clinical examination and selected imaging

The NHS explains that a GP will examine your leg and check for other health conditions that could be causing a Baker’s cyst. They may send you for an ultrasound or MRI scan, or refer you to a specialist for more tests or to rule out serious causes.

Imaging can confirm that the lump is a fluid-filled cyst, show its size and look at the knee problem behind it. When a clot is suspected, urgent tests are needed to rule it out. Not everyone needs a scan if the diagnosis is clear on examination.

07Underlying cause

Treating the underlying knee problem

Mayo Clinic explains that treating the root cause, such as managing arthritis or repairing cartilage damage, typically leads to improvement. The NHS agrees that if the cyst is caused by an underlying condition, symptoms usually get better when that condition is treated.

The NHS adds that a Baker’s cyst does not always need treatment and that, sometimes, particularly in children, it gets better on its own. Treatment options it lists include painkillers, a steroid injection in the knee and physiotherapy. Our guide on ice or heat for knee pain covers simple symptom relief.

08Self-care

Comfort and adapted activity

The NHS suggests these measures to ease pain and swelling while the cyst gets better, and after a rupture once a clot has been ruled out:

• rest the knee
• apply an ice pack wrapped in a tea towel for about 10 minutes at a time, repeating every few hours if needed
• raise the leg, for example on a pillow
• use simple painkillers if suitable for you

Walking is not always good or bad: activity can make symptoms worse, so it is usually adjusted to what the knee tolerates while the underlying problem is treated. A physiotherapist can help plan this. In our physiotherapy practice in Bilbao we offer individual rehabilitation for adults after medical assessment (consultations are in Spanish).

09Sources

Where the sources differ

Mayo Clinic and the NHS agree on the main causes and on treating the underlying knee problem, but differ in some details:

• Urgency. Mayo Clinic advises seeking care right away for pain and swelling behind the knee because, rarely, it can be a blood clot. The NHS divides signs into urgent (sudden worsening, warm or discolored skin) and emergency (breathlessness or chest pain).
• Drainage and surgery. Only the NHS lists draining fluid from the cyst and surgery to repair damage to the knee joint, adding that surgery to remove a Baker’s cyst itself is rare.
• Time course. The NHS says a Baker’s cyst can take a few months to a few years to get better, and that after a rupture symptoms are worse until the swelling goes down, which can take a few weeks. Mayo Clinic does not give timescales.
• Medicines. The NHS names specific painkillers; we mention only the groups. Anti-inflammatory painkillers are not suitable for everyone.

10Summary

In summary

A Baker’s cyst is a fluid-filled lump behind the knee, usually caused by arthritis, gout or a knee injury that makes the joint produce too much fluid. It may cause no symptoms, or pain, tightness and stiffness, often worse after activity. Many improve on their own or when the knee problem is treated, although this can take months or longer.

Have any new lump checked, and get urgent help if the leg suddenly becomes more painful, swollen, warm or discolored, or emergency help with breathlessness or chest pain. A simple record of which activities you tolerate, how far you can walk, how bending the knee feels and how the swelling changes helps you and your clinician review progress.