Baker’s cysts are a common cause of knee pain seen in the clinics of surgeons, doctors and physiotherapists. They are named after Mr Baker, and are not particularly prevalent amongst bakers, unlike ‘housemaid’s knee’ (properly called pre-patellar bursitis) which was definitely an issue for housemaids, but which is now more common in bricklayers and people who spend a lot of time kneeling. There are not too many housemaids around these days!

Any collection of joint fluid out the back of the knee is likely to be labelled a Baker’s cyst. In most cases a Baker’s Cyst simply reflects the fact that the knee is producing more fluid than normal. All joints constantly produce and recycle the synovial fluid which lubricates and nourishes the joint. Increased fluid usually means that the knee has a problem, and the Baker’s cyst is one of the symptoms, not the cause of the problem. The underlying cause of the problem can be varied but commonly relates to either an injury to the meniscus (fibrocartilage), or simple age-appropriate degeneration in the knee – good old “wear and tear”. Most Baker’s cysts tend to “come and go” – that is, they vary in size depending on how much fluid is in it, sometimes because of the variations in activity levels of the person with the cyst.

The above description is true for most patients who seek treatment for a Baker’s cyst, but occasionally a cyst may cause problems in and of itself. If a Baker’s cyst ruptures and the fluid leaks out into the surrounding soft tissues it can be very painful. Or, a cyst may become so large that it takes up space and puts pressure on other structures in the back of the knee. In these situations, it may be appropriate to have surgery in which the cyst will be removed and the joint lining (capsule) repaired.

There has been a measurable increase in the prevalence of Baker's cysts in recent decades, which mirrors the wider increase in knee pathology in general – for example, knee replacements are rising at a much higher rate than hip replacements and seem likely to continue to do so. It probably also reflects the ease with which high quality ultrasounds and MRI scans are obtained in clinical practice - we are finding more problems because we are doing more scans and the quality of scans keeps improving.

In summary, Baker’s cysts are rarely the primary cause of knee symptoms. They tend to indicate that something is going on with the knee, and it is the knee itself that the symptoms are coming from. Treatment should therefore be aimed at addressing the underlying cause (most commonly knee osteoarthritis), as well as treating the cyst itself. There are not many good quality research studies for the treatment of Baker’s cysts, however several studies have reported some evidence for the use of; ice packs, massage, compression, non-steroidal anti-inflammatories, aspiration and corticosteroid injections in managing symptoms¹. Horizontal therapy (a type of electrical current passed through the body) has been suggested as a helpful treatment for Baker’s cysts, however the research evidence is not strong, and a comparison of horizontal therapy with placebo treatment has not been performed for Baker’s cysts¹. A general exercise program focusing on mobility and strength has also been shown to decrease symptoms and will treat the underlying arthritis.