What is a Baker’s cyst

A Baker’s cyst or popliteal cyst, is a fluid filled lump or swelling behind the knee. It is usually caused by excess fluid that comes from the knee joint. The popliteal fossa is a diamond-shaped space on the posterior aspect of the knee bordered laterally by the tendons of the biceps femoris muscle and medially by the tendons of the semitendinosus and semimembranosus muscles.

Your knee is a large and complex joint where three bones meet—your thigh bone (femur), shin bone (tibia) and kneecap (patella). Surrounding the joint is a tough capsule filled with a lubricating fluid called synovial fluid. This fluid allows your knee to move freely. Small fluid-filled sacs, known as bursa, cushion the joint and help reduce the friction between tissues caused by movement. When your knee produces too much synovial fluid, the excess fluid causes the bursa behind the knee to expand and bulge. This is a Baker’s cyst. It may also be called a popliteal cyst. Baker’s cysts can vary in size.

People with a Baker’s cyst might also have arthritis or an injury such as a torn cartilage in their knee.

Baker’s cyst is caused when the tissue behind the knee joint becomes swollen and inflamed. The swelling and inflammation can cause:

• pain in the knee and calf
• a build-up of fluid around the knee
• occasional locking or clicking in the knee joint

However, sometimes a Baker’s cyst may not cause any symptoms other than the fluid-filled swelling at the back of the knee.

In rare cases, a Baker’s cyst can burst (rupture), resulting in fluid leaking down into your calf. This can cause sharp pain, swelling and redness in your calf.

Figure 1. Popliteal fossa (location of Baker’s cyst)

Figure 2. Baker’s cyst (popliteal cyst)

Baker’s cyst complications

The symptoms of a Baker’s cyst are usually mild, however sometimes complications can develop, such as:

• the popliteal cyst continues to grow, causing your symptoms to worsen
• the popliteal cyst may extend down into your calf muscles (dissection)
• thepopliteal cyst may burst (rupture) and cause bruising on the ankle of the affected leg, due to leaked fluid.

Occasionally Baker’s cysts become infected, grow bigger or can bleed. If you experience any swelling or warmth in your calf, you should seek medical advice quickly.

Sometimes a Baker’s cyst ruptures or bursts, causing pain and swelling in your calf. Your doctor may want to rule out a serious problem such as a blood clot (deep vein thrombosis).

It can be difficult to tell the difference between the complications of Baker’s cyst and more serious but less common problems such as a blood clot in the vein or inflammation of veins.

It is also important to seek medical advice, as more serious but less common problems can present in a similar way. These may include a tumor, deep vein thrombosis (DVT) or popliteal artery aneurysm. So it’s better to be safe and get it checked out.

Baker’s cyst cause

Knee damage caused by a sports-related injury or a blow to the knee can lead to a Baker’s cyst developing.

A lubricating fluid called synovial fluid helps your leg swing smoothly and reduces friction between the moving parts of your knee.

But sometimes the knee produces too much synovial fluid, resulting in buildup of fluid in an area on the back of your knee (popliteal bursa), causing a Baker’s cyst.

Some of the common causes of Baker’s cyst include:

• injury – trauma or injury to the knee can cause a build-up of excess fluid
• torn cartilage – cartilage is a thin cushion on the ends of your bones
• arthritis – particularly rheumatoid arthritis and osteoarthritis
• infection – can cause fluid to build up around the knee joint
• unknown causes – Baker’s cysts can sometimes develop for no apparent reason.

A Baker’s cyst can also sometimes occur if you have a health condition such as:

• osteoarthritis – usually caused by age-related “wear and tear” of joints; it particularly affects the knees, hips, hands and big toe
• inflammatory arthritis – including rheumatoid arthritis which is a less common type of arthritis and is caused by the immune system attacking the joints
• gout – a type of arthritis that usually affects the big toe and is caused by a build-up of the waste product uric acid in the blood

Baker’s cysts are more common in women than men, probably because women are more likely to develop osteoarthritis and rheumatoid arthritis. They usually develop in people aged over 40, although can affect people of any age, including children.

Baker’s cyst prevention

Knee joints are susceptible to injury during sporting activities. Preventing knee injuries from occurring can reduce the risk of a Baker’s cyst developing in the first place or coming back. Things you can do to prevent knee injuries:

• warm up and cool down before and after exercising or playing sports
• wear supportive footwear
• try to turn on the balls of your feet, rather than through your knees to help avoid knee injuries
• if you injure your knee, stop your activity immediately, apply ice packs to treat the swelling and seek medical advice.

Baker’s cyst symptoms

If the Baker’s cyst is small, often there are no symptoms and you may not even know you have a cyst.

Otherwise, you may have aching, a swelling or lump behind your knee, or feel pressure when you straighten your leg.

If symptoms do occur, they can include:

• swelling behind the knee
• pain
• stiffness or tightness of the knee.

Your doctor can often diagnose a Baker’s cyst by examining your knee and shining a torch through the lump.

You might also have an ultrasound or MRI scan.

Baker’s cyst diagnosis

A Baker’s cyst may diagnosed using a number of different methods, including:

• physical examination of your knee
• taking your medical history to see if you have any conditions that may cause a Baker’s cyst (e.g. rheumatoid arthritis)
• x-ray – this won’t show the cyst, but may show arthritis in the knee that may be causing the problem
• shining a light through the cyst (transillumination) – to see if the mass is filled with fluid
• ultrasound or magnetic imaging resonance (MRI).

Baker’s cyst treatment

Treatment won’t usually be necessary if you have a Baker’s cyst that isn’t causing any symptoms as they can get better and disappear on their own.

If you have an underlying condition that’s causing your cyst, it’s important that the condition is properly managed. The cyst may disappear when the condition causing it has been treated.

If the Baker’s cyst is associated with arthritis or a knee injury, then treating these conditions can help.

Baker’s cyst natural treatment

• If a child has a painless Baker’s cyst, it can usually be left alone. In children, most Baker’s cysts disappear eventually without treatment.

• For adults you can ease any pain from a Baker’s cyst with cold packs, or by taking over-the-counter painkillers like paracetamol or non-steroidal anti-inflammatory drugs (NSAIDs), such as ibuprofen, to reduce swelling and pain in the affected knee. A bag of frozen peas wrapped in a tea towel works well as an ice pack. Hold an ice pack to your knee for 10-20 minutes to reduce any swelling – never put ice directly on your skin.
• Use compression bandages to support your knee joint – you can buy these from a pharmacy.
• The pain may also ease with physical activities such as walking, swimming or Tai Chi. If you are overweight, losing weight may help.
• Temporarily avoiding activities that aggravate your knee joint, use crutches to take the weight off your knee
• Physiotherapy, which may include heat or ice treatment and exercises and stretches to maintain the mobility and strength of your knee

Taking supplements or wearing a brace is unlikely to help with your symptoms.

If you have a troublesome Baker’s cyst, your doctor may drain it using an ultrasound and inject it with corticosteroids, which has been shown to result in significant improvements and a low chance of the cyst coming back.

For some people, surgery may be required in some cases to remove the cyst if all other treatments haven’t worked. For example, repairing a torn cartilage might help. Removing the cyst alone isn’t helpful, as it usually recurs unless the underlying cause is addressed.

Your doctor can advise you on the treatment options that are best for you.

Surgery to repair knee damage

In some cases, it may be possible to drain (aspirate) a Baker’s cyst. However, it may not be possible to aspirate long-term (chronic cysts) because they’re made of jelly.

Surgically removing a Baker’s cyst isn’t easy because unlike other types of cyst, they don’t have a lining.

Surgery may be needed to repair your knee joint if it’s significantly damaged as a result of an injury or a condition such as osteoarthritis.

A type of keyhole surgery called arthroscopy is usually used. The surgeon will use an instrument called an arthroscope to look inside your knee joint. Small surgical instruments can be used alongside the arthroscope to repair any damage.

Treating a ruptured Baker’s cyst

A Baker’s cyst can often rupture (burst), resulting in fluid leaking down into your calf. This causes a sharp pain in your calf which becomes red, swollen and tight.

The fluid will gradually be reabsorbed into the body within a few weeks. The recommended treatment for a ruptured cyst is rest and elevation (keeping the affected calf raised).

Prescription painkillers – usually a combination of paracetamol and codeine – can also be used to control any pain. See your doctor for a prescription.

Lifestyle and home remedies

If your doctor determines that arthritis is causing the cyst, he or she may advise you to take some or all of the following steps:

• Follow the R.I.C.E. principles. These letters stand for rest, ice, compression and elevation. Rest your leg. Ice your knee. Compress your knee with a wrap, sleeve or brace. And elevate your leg when possible, especially at night.
• Try over-the-counter pain-relieving medications. Drugs such as ibuprofen (Advil, Motrin IB, others), naproxen sodium (Aleve, others), acetaminophen (Tylenol, others) and aspirin can help relieve pain. Follow the dosing instructions on the package. Don’t take more than the recommend dosage.
• Reduce your physical activity. Doing so will reduce irritation of your knee joint. Your doctor can offer you guidance on how long you need to reduce your activity levels, and he or she may be able to suggest alternative forms of exercise you can do in the meantime.