Knee Injection
Knee injection. Click to enlarge

Viscosupplementation is a medical procedure during which lubricating fluid is injected into a joint. Also called hyaluronic acid injections or hyaluronan injections, viscosupplementation is most commonly used to treat symptoms of symptoms of knee osteoarthritis.

Hyaluronic acid is a key component of the joint fluid in healthy joints, but is found in lower concentrations in osteoarthritic joints

By adding hyaluronic acid to the existing joint fluid of an osteoarthritic knee, the goal is to:

  • Facilitate better knee movement
  • Reduce pain
  • Perhaps slow osteoarthritis progression
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Typical candidates for viscosupplementation are people with knee osteoarthritis who have failed to improve with other non-surgical treatments.

Following the injections, it is generally recommended that patients engage in a rehabilitation program that includes gentle, progressive knee exercise. The goals of rehabilitation are to improve range of motion and develop muscle strength to support the knee.

How Viscosupplementation Works

During viscosupplementation a small amount of hyaluronic acid, often just 2 mL, is injected directly into a joint capsule.

A healthy knee joint has up to 4 mL of joint fluid within the joint capsule.1,2 Hyaluronic acid is a key component of the joint fluid. It gives the joint fluid its viscous, slippery quality, which does the following:

  • Enables the bones' cartilage-covered surfaces to glide against each other, thereby reducing joint friction
  • Adds cushion to protect joints during impact (e.g. weight-bearing activity)

Joints affected by osteoarthritis typically have a lower concentration of hyaluronic acid in their joint fluid than healthy joints, and therefore less protection against joint friction and impact. Experts believe this further accelerates the joint degeneration process, setting in place a vicious cycle.

As its name implies, viscosupplementation artificially supplements the joint fluid's natural viscosity. By injecting a man-made hyaluronan into the knee, doctors hope to temporarily lubricate the knee joint, thereby decreasing pain improving function and perhaps even slowing the degeneration process.

Hyaluronic Acid Injections for the Hip and Other Joints

The United States FDA has approved viscosupplementation for treating knee arthritis only, but treating hip osteoarthritis or other joints with viscosupplementation is permitted. Some doctors have found some patients respond to viscosupplementation for the hip, shoulder and ankle, but there is relatively little published research regarding its efficacy.

Using viscosupplementation for a joint other than the knee is considered an "off label" use of the injectable fluid. Insurance companies may consider the procedure "experimental" and not cover the cost, so patients should check with their insurance companies if considering viscosupplementation for hips or other joints.

References

  1. Mundt L, Shanahan K MS MT(ASCP), Graf's Textbook of Routine Urinalysis and Body Fluids (p.255), Philadelphia, Pa: Lippincott Williams & Wilkins; 2011
  2. MUSC Health Synovial Fluid Analysis. Medical University of South Carolina. http://www.muschealth.com. Accessed July 11, 2012.
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Written by Vijay B. Vad, MD
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