Introduction
Anatomy
Cause
Symptoms
Diagnosis
Non-surgical treatment
Surgical treatment
Rehabilitation
A Baker cyst (also known as popliteal cyst) is swelling caused by fluid from the knee joint protruding to the back of the knee. It is a benign condition without malignant tendency.
The lubricating fluid (synovial fluid) produced by the knee joint passes in and out of various tissue pouches (bursae) throughout the knee. For certain reason, if the knee produces too much fluid, some of it may seep out or push through the lining, forming a sac. Baker cyst is the sac that forms between two muscles called gastronemius and semimembranosus around the back of knee.
Any cause that irritates the knee joint to produce excessive synovial fluid may result in Baker’s cyst formation. These includes:
degenerative osteoarthritis
inflammatory arthritis, e.g. rheumatoid arthritis
trauma e.g. meniscal tear
gout, pseudogout
A swelling behind the knee (the commonest presentation, up to 78% in one study)
A sensation of pressure behind the knee which can go down into the calf muscle.
Difficulties in bending the joint.
Aching and tenderness after exercise.
If the cyst ruptures, it may cause severe pain around the leg, mimic a condition called deep vein thrombosis (a blood clot in the leg’s vein)
The diagnosis of Baker’s cyst can usually be done by doctor’s exam. One typical test is to turn all lights out and shine a torch through the lump, we should see a red glow around the lump indicating that it is filled with fluid. Ultrasound and MRI can further confirm the diagnosis.
If the cyst is not causing any problem, the doctor may prefer to observe. But if it is symptomatic, there are several options of treatment:
Physiotherapy
Ice, a compression wrap may help reduce pain and swelling. Gentle mobilization and strengthening exercises for the muscles around the knee may also help to reduce the symptoms and preserve knee function.
Fluid drainage
The fluid from the knee joint can be drained by using a needle. This is called needle aspiration and can be performed with or without the help of ultrasound
Steroid injection
Injecting steroid into the area of the cyst can help to reduce swelling and pain, and usually this is done in conjuncture with needle aspiration
Nonsurgical treatments are usually most effective when the underlying cause of the cyst is addressed. In other words, the effects of arthritis, gout, or injury to the knee need to be controlled.
If the nonsurgical treatment fails, patient may consider to have their cyst excised. This can be done either by open surgery or arthroscopic excision
Arthroscopic
The surgeon can put in the camera and the tools through very small wounds made over the knee, such that the communication between the cyst and the knee joint can be sutured or destroyed. However, the opening may sometimes difficult to be identified.
Open surgical excision
It is indicated if conservative measures or arthroscopic intervention fail. An incision in the skin over the cyst, at the back of the knee is made. The stalk leading from the cyst down to the joint can often be located and sutured over or cauterised, after which the cyst can be removed
Most common complication is recurrence. Since the cyst forms very near to major blood vessel and nerve, it is possible that these structures can be injured during surgery.
After surgery, daily activities and work can be resumed as soon as patient is able. We advise patient to elevate the knee for several days to avoid swelling. Vigorous exercise should be avoided for the first few weeks. Physical therapy can help to mobilize the knee joint and strengthen the muscles.
Dr. August FOK