What is a Baker's cyst?
A Baker's cyst, also known as a popliteal cyst in adults, is a fluid-filled sac that forms at the back of your knee. It can vary in size as the fluid content varies.
What causes a Baker cyst?
A Baker's cyst is normally the result of a knee injury or joint disorder that causes inflammation inside the knee, such as osteoarthritis, rheumatoid arthritis or meniscus tear.
In response to the inflammation, the knee produces an excess of synovial fluid which is able to pass into the popliteal bursa at the back of the knee. When fluid accumulates in the bursa causing it to bulge it is called a Baker's cyst.
What are the symptoms of a Baker's cyst?
Many people that have a Baker's cyst are unaware of it because the majority of cases do not have any symptoms. The first time you may become aware of it is if you feel a bulge at the back of the knee or you experience a restriction in your range of motion when bending to kneel or to do a squat. Sometimes the bulge is so large that you may struggle to fully bend or straighten the knee.
A Baker's cyst can cause pain at the back of the knee and calf region. Symptoms can change depending on the position of the knee.
What are the potential complications of a Baker's cyst?
Ruptured cyst - On rare occasions, a Baker's cyst can rupture causing pain, warmth and redness in the region of the calf muscles. The appearance and symptoms are similar to a deep vein thrombosis (DVT)/blood clot, or infection (cellulitis) both of which are conditions that require urgent medical attention.
Not every swelling at the back of the knee is a Baker's cyst. There is always the possibility of a soft tissue tumour which your doctor will look to rule out.
If you develop a pain in your calves, with or without warmth, redness and swelling you should make an appointment to see a doctor urgently.
How is a Baker cyst diagnosed?
Diagnosing a Baker's cyst involves getting your medical history and performing a physical examination to look for conditions that can contribute to the formation of the cyst.
A diagnostic ultrasound scan can be carried out on the same day of your appointment to confirm the diagnosis. X-rays of the knee joint or other blood tests may be requested if an underlying condition is suspected.
Magnetic resonance imaging (MRI) are not routinely requested, but more often painless Baker's cysts are incidentally found when MRI scans are done for other reasons, such as when investigating the cause of joint pain.
What are the treatment options?
Most Baker's cysts are not problematic, so if you don't get any symptoms from it you don't need treatment.
Aspiration (fluid-drainage) and injection of a corticosteroid and local anaesthetic can be done if a Baker's cyst is symptomatic. This is ideally done using ultrasound guidance to provide real-time visualisation of the needle placement and avoid injury to nearby blood vessels.
Chances of re-accumulation of synovial fluid following drainage of a Baker's cyst is high, but this may be reduced by addressing the underlying cause of the cyst in the first place. For example, if your cyst is a result of having osteoarthritis of the knee joint this will also need addressing.
Before undergoing drainage of a symptomatic Baker's cyst make sure any underlying cause has been explored and addressed, otherwise you risk having rapid re-accumulation.
What is a bursa?
Bursae (plural) are thin, closed, fluid-filled sacs that provide a gliding surface to reduce friction between bone and the surrounding soft tissue structures hence, they are commonly found around joints. They are lined with synovial membrane and normally filled with a sliver of fluid.
Bursitis is inflammation of a bursa characterised by thickening of the synovial lining and accumulation of excess fluid.
What is prepatellar bursitis?
Prepatellar bursitis is inflammation of the prepatellar bursa, the thin fluid-filled sac positioned in front of the kneecap (patella).
Causes of prepatellar bursitis
- Pressure from frequent kneeling is a common cause so occupations that require this position (plumbers, roofers, carpet layers, and gardeners) are at greater risk of developing the condition. The alternative name of housemaid's knee reflects the predominant group that developed the condition when it was first described.
- An acute trauma from a blow to the front of the knee or a fall.
- Overuse - Repetitive bending of the knee with activities like cycling or squatting can trigger the condition.
- Recurrence - If you have had bursitis before it can reoccur sometimes without a clear trigger.
- Infection - When kneeling it is possible for a small sharp object to break the skin and introduce infection causing a septic bursitis.
- People with a low grade systemic inflammatory condition like gout, rheumatoid arthritis or tuberculosis, or patients with diabetes mellitus, are more susceptible to developing prepatellar bursitis.
What are the symptoms of prepatellar bursitis?
Symptoms of acute bursitis include tenderness at the site of the bursa, redness, warmth, swelling, and loss of range of motion. Worsening pain, spreading redness, feeling fatigued and generally unwell should raise suspicion of a septic bursitis.
Chronic bursitis can be a painless swelling of the bursa. Even after the swelling settles you may feel nodules or crepitus over the front of the knee.
If you think you might have septic bursitis you should arrange to see your physician urgently.
How do you diagnose prepatellar bursitis?
Making a diagnosis from the medical history and physical examination is fairly straight forward. An in-clinic ultrasound scan can be used to confirm the fluid is in the bursa in front of the knee and not in the knee joint itself.
X-rays may be ordered if there is suspicion of a fracture or a foreign body in the soft tissue. In addition, blood tests may be performed to rule out infection or a medical condition.
If there is concern over the possibility of infection aspiration (drainage) of the bursal fluid may can be carried out and the content sent to the laboratory for analysis.
Prepatellar bursitis affects all age groups, but is more likely to be septic when it occurs in children.
How do you treat prepatellar bursitis?
Treatment depends on how severe the problem is, whether it is an acute or chronic case and whether it is an aseptic (not infected) or septic (infected) bursitis.
Acute cases will respond well to rest and nonsteroidal anti-inflammatory drugs. Fluid removal (aspiration) and corticosteroid injection, administered under ultrasound guidance, is routinely used for cases that do not settle with the initial conservative measures.
Chronic cases may need surgery to remove any loose bodies or fragments within the bursa.
Infected cases need urgent medical attention for antibiotic treatment and rarely drainage.
The treatment plan also includes advice about avoiding further aggravating factors like excessive weight bearing, repetitive movements, and poor posture.
