Joint Effusion Examination and Treatment

Abnormal Accumulation of Fluid in or Around a Joint

Joint effusion of elbow
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Joint effusion (not to be confused with joint fusion) is an abnormal accumulation of fluid in or around a joint. You may have heard of "water on the knee" or "fluid on the knee"—layman's terms for joint effusion of the knee. Aseptic joint effusion means that the cause is not a bacterial infection. Possible causes include viral infection, physical trauma, or arthritis (especially inflammatory types of arthritis).

A small amount of fluid exists in normal joints. When a joint is affected by inflammatory arthritis (e.g., rheumatoid arthritis), abnormal fluid build-up is not uncommon. When this occurs, the joint appears swollen. There may also be joint pain, redness, warmth, and decreased range of motion occurring along with joint effusion. 

Physical Examination

Your doctor will need to examine the joint and determine if there is soft tissue swelling secondary to joint effusion or if there is swelling of periarticular tissues (i.e., the tissues around a joint). Your doctor will look for visible evidence of swelling by searching for deviation from the normal shape of the joint and by comparing it to the same joint on the opposite side of the body.  

The doctor then will palpate (examine by touch) the affected joint. A normal synovial membrane is too thin to palpate, but a thickened synovial membrane which is associated with many types of inflammatory arthritis may have a boggy feel upon palpation.

With palpation, the doctor will try to differentiate between synovial proliferation (thickening) and effusion. Ultrasonography is also sometimes used to make the distinction. Recognition of joint effusion is useful when formulating a diagnosis.

Features of Joint Effusion on X-ray

Joint effusion is not easily recognized on plain x-rays.

But, there are certain characteristics which, if seen on x-ray, are associated with joint effusion. With knee joint effusion, the effusion appears as a rounded homogeneous soft tissue density within the suprapatellar recess. The effusion separates the periarticular fat pads and blocks the quadricep tendon on x-ray. Elbow joint effusion is associated with a characteristic sail sign. On x-ray, the elbow joint effusion displaces the fat pads around the distal humerus. The resulting triangular appearance resembles a sail. Ankle joint effusion is associated with a teardrop-shaped soft tissue density, which displaces the anterior fat pad. Hip joint effusions are very difficult to identify on plain x-ray. Ultrasound, CT scan, and MRI are more effective imaging modalities for finding hip joint effusion.

Draining Joint Fluid for Analysis

Your doctor will likely drain fluid from the affected joint (i.e., joint aspiration) to help relieve pressure in the joint while reducing pain and other symptoms. If an infection is not suspected, your doctor may decide to inject a small amount of cortisone in the affected joint to reduce inflammation and prevent the fluid from building up again.

Studying the aspirated joint fluid can help with diagnosis.

For example, in someone with a warm and/or red knee, there is a chance that the joint is infected. Sending the fluid to the laboratory for culture can help confirm or rule out an infection. In addition, a blood cell count on the fluid can be obtained. If there are many white blood cells in the specimen, the fluid may be cloudy. Cloudy fluid may develop in patients with infection, rheumatoid arthritis, or gout. Joint fluid associated with gout may have a golden color. In people with osteoarthritis, the fluid is often clear. In those who have injured their knee, the fluid may be clear or bloody.

From synovial fluid test results, joint effusion can be categorized as inflammatory, non-inflammatory, septic, or hemorrhagic.

  • Noninflammatory: Synovial fluid with a cell count of less than 2,000 white blood cells/mm3 is noninflammatory.
  • Inflammatory: Synovial fluid with a cell count of 2,000 white blood cells/mm3 or greater is categorized as inflammatory.
  • Septic: Septic effusions (due to bacteria, mycobacteria, or fungus) have an inflammatory white cell count, equal or greater than 20,000 white blood cells/mm3.
  • Hemorrhagic: The presence of a significant number of red blood cells in synovial fluid is suggestive of a hemorrhagic condition.

Treatment of Joint Effusion

Once the joint fluid has been drained, nonsteroidal anti-inflammatory drugs (NSAIDs), acetaminophen, and immobilization of the affected joint are typically part of a treatment regimen for aseptic joint effusion. The goal is to prevent a recurrence of the abnormal accumulation of joint fluid and to manage the underlying condition.


Brief Overview of Aseptic Joint Effusion (Fluid in a Joint).

Dixon, Andrew MD et al. Joint Effusion.

Kelley's Textbook of Rheumatology. Ninth edition. Elsevier. Chapter 40. History and Physical Examination of the Musculoskeletal System. Swelling.

Sholter, Dalton E. MD, et al. Synovial Fluid Analysis. Categories of Joint Effusion. UpToDate. January 18, 2017.