A painful lump that forms behind the knee is called a Baker cyst or a popliteal cyst. The fluid-filled lumps cause pain and discomfort, and stiffness, making walking challenging. The pain can get more acute when moving around or when the knee is fully straight or bent. Women are more likely than men to develop this condition due to rheumatic arthritis and osteoarthritis. While some cysts may go away in time, some may need expert attention.

Causes of Baker cyst
The ligaments, tendons, and bones make up the knee. The synovial fluid lubricates the tendons and cartilage, enabling the legs to work freely and minimize friction. In each knee, numerous pouches named bursae allow joint fluid to move around. In addition, a valve-like mechanism controls the movement of synovial fluid between the popliteal bursa (a pouch at the rear of the knee and the knee joint).
The popliteal bursa can get full of synovial fluid if the knee makes an excess of it. This can be triggered by swelling of the knee joint, which is usually caused by a deeper problem like:

• Gout
  Gout happens when the amount of uric acid in the blood rises as long as it’s too high (hyperuricemia), which causes the urate crystals to form all around the joints. This leads to swelling and a lot of pain.
• Hemophilia
  Hemophilia is a health disease that is passed down from parent to child in which the blood doesn’t clot properly, causing damage to the joints and internal bleeding.
• Lupus
  A condition known as lupus causes the immune system of the body to target healthy, typical tissue.
• Osteoarthritis
  Osteoarthritis is arthritis when joint cartilage gets inflamed, breaks down, and erodes over time.
• Psoriasis
  Psoriasis can cause joint discomfort and irritation in some people.
• Reactive, rheumatoid, and septic arthritis
  Reactive arthritis is a type of arthritis that lasts for a long time and causes swollen eyes, joints, and the genital, bladder, or digestive systems.
• Injury
  A knee injury or traumatic event, like a torn cartilage, can cause a Baker’s cyst.

Symptoms of Baker cyst
Baker’s cysts are uncommon, but they can cause various symptoms when they occur.

• A lump or growth behind the knee that is full of fluid. It may appear to be a water-filled balloon.
• The knee feels stiff
• Inability to fully extend the leg and restricted mobility
• Pain in the knee
• Pain in the legs
• Knee joint that clicks, locks, or buckles
• Rupture of the cyst

Diagnosis for Baker cyst
Most of the time, this cyst can be found during a physical check. To find out more, your doctor might require tests for imaging, such as:

• Ultrasound
  An ultrasound is a simple, easy test using sound waves to determine if the lump is solid or liquid.

• X-ray
  Although it may not detect the Baker cyst, this procedure can identify knee arthritis. One of the things that can cause this cyst is arthritis.

• Magnetic resonance imaging (MRI)
  An MRI uses magnetic waves to show detailed pictures of what’s happening inside the body. It can help the doctor to understand the condition better.

Treatment for a Baker cyst
Exercises that are easy on the knee but still increase the range of motion and build the muscles around it may help the knee feel better and keep it functioning normally if other treatments fail. Surgery is only used when other treatments fail to alleviate the pain and the person is still unable to walk or do other things.

• Prescription treatments for a Baker cyst
  NSAIDs (nonsteroidal anti-inflammatory prescription treatments) can treat Baker’s cysts. These are painkillers and fever reducers that don’t contain steroids.
• Physical therapy
  A trained physical therapist may suggest that you do some gentle exercises to improve your knee muscles and increase their range of motion. These workouts can help lessen discomfort and keep the knee working well.
• Arthroscopy
  If there is a lot of damage to the knee joint, which could be caused by a physical accident or an underlying illness, the cyst may need to be removed and the joint fixed. A thin, bendable fiber-optic tube called an arthroscope is put into a joint through a small cut so the surgeon can look for problems and fix them.

If you experience any pain and stiffness behind your knee, it is advised to consult a licensed specialist at the earliest. It is essential to diagnose the condition and prevent any progression of any other underlying condition. A lump behind the knee could indicate something more serious, like a tumor or aneurysm.