Baker's cyst: treatment, symptoms, causes and when to get help

The NHS says a Baker's cyst does not always need treatment. Sometimes, particularly in children, it will get better on its own. If it is caused by an underlying condition, your symptoms will usually get better when that condition is treated. Other treatments can include painkillers, a painkilling injection (hydrocortisone injection) in your knee, physiotherapy, draining fluid out of the cyst, and surgery to repair damage to your knee joint. The NHS says it is rare to have surgery to remove a Baker's cyst.

NICE Clinical Knowledge Summaries (CKS) says that in adults management involves identifying and optimising management of any underlying conditions such as osteoarthritis or rheumatoid arthritis, advising that no treatment is required if the cyst causes no symptoms, and considering simple pain relief (such as paracetamol or ibuprofen) and physiotherapy if symptoms are troublesome. It suggests referral to a rheumatologist or orthopaedic surgeon if the diagnosis is unclear, the cyst is troublesome despite conservative measures, or it is very large.

The NHS says the main symptom of a Baker's cyst is a soft lump at the back of the knee, and the fluid-filled lump may be more visible when standing up. The lump may be your only symptom, but you may also have knee or leg pain, tightness, stiffness or aching in your knee, difficulty bending your knee, and clicking in your knee. Your symptoms may be worse after walking.

NICE CKS lists complications of Baker's cysts as chronic pain, dissection or rupture, bleeding, compression of adjacent structures and infection.

• A soft lump at the back of the knee

• Knee or leg pain

• Tightness, stiffness or aching in the knee

• Difficulty bending the knee

• Clicking in the knee

• Symptoms that are worse after walking

The NHS says to ask for an urgent GP appointment or get help from NHS 111 if you have pain or swelling in your leg that suddenly gets worse, swelling, bruising and warm skin on your leg, red or darkened skin on your leg (which can be harder to see on brown or black skin), or swelling in your leg that gets harder or softer. It says these could be symptoms of a burst cyst (rupture) or a blood clot in the leg called deep vein thrombosis (DVT).

The NHS says to call 999 or go to A&E if you have symptoms like pain and swelling in your leg and also breathlessness or chest pain, as these could be symptoms of a blood clot that has travelled to the lungs (pulmonary embolism), which can be life-threatening and needs treating immediately. Do not drive yourself to A&E.

NICE CKS says that when a serious alternative diagnosis such as DVT is suspected, same-day assessment in secondary care should be arranged for adults, and urgent assessment for children. If a cyst has burst, the NHS says symptoms will be worse than normal until the swelling goes down, which can take a few weeks.

NICE CKS says Baker's cysts (also known as popliteal cysts) are not true cysts. They are a distension of the gastrocnemius-semimembranosus bursa behind the knee. It describes them as primary (not associated with underlying disease of the knee joint, found mainly in children) or secondary (associated with underlying disease of the knee joint, and tending to have a communication between the bursa and the rest of the knee joint). Almost all Baker's cysts in adults are secondary.

The NHS describes it as a fluid-filled lump at the back of the knee, which may get better on its own or by treating the condition causing it, and says you should get any lumps checked by a GP.

The NHS says sometimes there is no particular cause, especially in children. In adults they usually happen when another health condition causes damage to the knee joint, like a knee injury, osteoarthritis or rheumatoid arthritis, or gout. Anyone can get one, but they are more common in people aged 35 to 70.

NICE CKS says that in adults they are usually secondary to arthropathies such as osteoarthritis and rheumatoid arthritis, or soft tissue injury such as meniscal tears or anterior cruciate ligament damage. In children, development of primary cysts may be related to trauma or local irritation of the bursa, and secondary cysts may occur with conditions such as juvenile idiopathic arthritis and osteochondritis dissecans.

The NHS says the 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 any serious causes.

NICE CKS says assessment involves asking about swelling and knee joint symptoms, considering underlying causes and complications such as cyst rupture and serious alternative diagnoses such as DVT, and examining the knee. It says an ultrasound scan should be arranged to confirm the diagnosis and rule out serious alternative diagnoses in children, while history and examination may be sufficient to confirm the diagnosis in adults.

The NHS says there are things you can do to ease the pain, swelling and other symptoms while it gets better, which can also help if a cyst has burst. It suggests resting your knee gently, applying an ice pack (or a bag of frozen vegetables) wrapped in a tea towel to your knee for around 10 minutes at a time and repeating every few hours if needed, raising your leg on a pillow, and taking ibuprofen or paracetamol to help with pain and swelling.

The NHS says that sometimes, particularly in children, a Baker's cyst will get better on its own. NICE CKS says that for children, management involves reassuring the child and parents or carers that primary Baker's cysts usually resolve without treatment if no underlying disease is suspected and the diagnosis is confirmed on ultrasound.

NICE CKS says referral to a paediatric orthopaedic surgeon or paediatric rheumatologist is suggested if symptoms are troublesome, the cyst is very large, underlying joint disease is suspected or the diagnosis is unclear. It describes a peak in incidence between 4 and 7 years of age, with a larger peak between 35 and 70 years.

On the NHS, a GP is the first step; the GP can arrange an ultrasound or MRI scan or refer you to a specialist. NICE CKS suggests referral to a rheumatologist or orthopaedic surgeon if the diagnosis is unclear or the cyst is troublesome despite conservative measures.

If you see a private clinician, ask what is causing the cyst, whether a scan has excluded a blood clot in the leg, and who will treat the underlying knee problem, since the NHS says symptoms usually get better when the underlying condition is treated.