The inner lining of the knee joint is called synovial lining. The watery fluid secreted by this lining is called synovial fluid which acts as a lubricant during knee movement.
Fluid on the knee occurs when there is an accumulation of synovial fluid, blood or pus. In medical terms this condition is called knee effusion.
There are multiple causes of fluid on the knee. The type of knee effusion depends on the various causes outlined below.
- Trauma – Any injury to the structures which constitute the knee joint may result in fluid on the knee. Usually there is a collection of blood in the knee. Ligamentous injury involving anterior or posterior cruciate ligaments, medial or lateral collateral ligament.
- Fracture of the bony surface of the knee – These are lower end of femur fractures or upper end of tibia fractures.
- Patellar fracture – Knee dislocation or knee fracture.
- Meniscus injury – Meniscus is a C shaped cartilage. Two such cartilages are present in each knee and their injuries are especially likely to occur during contact sports.
- Polyarthritis – Inflammation of a joint is called arthritis. When this condition involves multiple joints, it is called polyarthritis. The inflammation of the synovial lining results in excessive production of synovial fluid which accumulates inside the knee (also see: bursitis). Some of the diseases which cause polyarthritis include:
- Reiter’s Syndrome
- Rheumatoid Arthritis
- Infection – Infection is caused by bacteria. This is more common in people with diabetes, poor nutritional status and in patients with poor immunity. Types of infections that can cause fluid on the knee include:
- Lyme disease
- Gout – Uric acid levels in the blood are increased leading to the formation of urate crystals in knee, also known as gout.
- Pseudogout – Deposition of calcium pyrophosphate crystals in knee result in fluid collection.
- Tumors – Tumors can be benign or malignant (cancerous). Benign tumors include aneurysmal bone cyst, fibrous dysplasia, osteochondroma, osteoid osteoma. Malignant tumors include chondroblastoma, eosinophilic granuloma, giant cell tumor, Ewing’s sarcoma, osteosarcoma and synovial sarcoma.
A patient with fluid on the knee may be completely asymptomatic or may have symptoms described below. When the accumulation of fluid on the knee is sudden, it is associated with symptoms. Whereas if the fluid collects slowly over weeks, the patient may be completely asymptomatic.
The symptoms of fluid on knee include:
- Swelling of the knee – The knee appears swollen. This swelling appears immediately after injury as in a fall, vehicular accident or sports injury. In other conditions, the fluid collects slowly over many days.
- Pain – This is a primary symptom in patients with an injury, infection and Gout. In sudden collection of fluid, stretching of the joint capsule also adds to the pain. Pain may radiate downwards due to irritation of the nerves. It is aggravated on movement or on bearing weight. Keeping the knee still may provide partial knee pain relief.
- Redness of surrounding skin – This indicates inflammation or infection.
- Increased temperature – The skin over the knee feels warm.
The diagnosis of fluid on the knee and its causes requires an assessment by a physician. A complete history of the condition is taken followed by a thorough physical examination. This is followed by knee related exams depending on the suspected cause. These knee exams include:
- Blood test – A blood test is used to detect other causes such as Gout or Pseudogout.
- Aspiration of joint fluid – Joint fluid is sent for bacterial, chemical and cytological examination.
- Imaging – X-ray or Magnetic resonance imaging (MRI) of the knee is used to look for certain types of injuries or tumors.
The treatment of fluid on the knee depends on its cause and severity of symptoms.
- RICE therapy – Rest, Ice application, Compression with bandaging, Elevation to reduce swelling. This method is specially used in sports injuries. To read more about RICE please click here.
- Aspiration – In chronic conditions and where the cause is not found, the fluid is aspirated with a syringe on multiple locations. There is always a risk of introducing infection into the knee, so all aseptic and antiseptic precautions should be taken.
- NSAID’s – Non Steroidal Anti-Inflammatory Drugs provide symptomatic knee pain relief.
- Antibiotics – Antibiotics used in patients with evidence of knee infection might be recommended by your doctor.
- Corticosteroids – Corticosteroids have chemicals that assist in reducing inflammation.
- Arthroscopy – A fine telescope of 4 to 6 mm diameter is used for diagnosis and treatment of internal injuries of the knee. In presence of infection, this is used for irrigation or washing of the knee with saline.
- Joint replacement – In patients who have a badly damaged joint surface, a prosthesis is recommended.
Prevention of fluid on the knee is not always possible especially when injuries occur. However, it is important to check yourself regularly as knee joints play a major role in knee movement. The following might help prevent fluid on the knee:
- Undue exertion or overuse should be avoided.
- Regular medication to keep diseases like Gout and Pseudogout under control.
- Regular exercise to keep the muscles around the knee strong and healthy.
- Maintain a healthy lifestyle.
- Workout with good form and technique.
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