Osteoarthritis (OA) is the most common form of arthritis. It affects more than 30 million people in the United States alone. OA is sometimes called degenerative joint disease, because it is caused by the wear-and-tear of a joint’s cartilage, the tissue that covers the ends of bones and provides cushion over many years of use. OA can also be caused by an injury to the joint, obesity, or genetics.

Healthy cartilage acts as a “shock absorber” and prevents your bones from taking the full impact of everyday walking, running, twists, and falls. A healthy knee also contains sufficient synovial fluid, a thick, gel-like liquid that reduces friction in the joint. A substance in the synovial fluid called hyaluronic acid acts as the joint’s “grease” and provides lubrication between bones and cartilage.

As cartilage begins to wear away and the amount of synovial fluid in the joint decreases, you may begin experiencing symptoms of OA. The most common signs of OA of the knee include:

  • pain at the joint
  • tenderness
  • stiffness
  • loss of flexibility

Over time and without treatment, the symptoms can become more severe, and the OA may cause loss of motion and bone spurs (bone growths around the affected joint). In the most severe cases, the cartilage can disappear entirely. This results in a very painful form of OA that typically can only be treated with total knee replacement.

While there is no cure for OA of the knee, several treatment options may ease the symptoms and possibly slow down the condition’s progression. Doctors may begin treatment with a very conservative approach, asking you to first try exercise, physical therapy, and even weight loss to reduce the pain and inflammation.

If these treatments prove ineffective or are no longer effective as your OA worsens, doctors may need to consider more aggressive treatments.

In the search for less invasive treatments that provide greater relief, researchers discovered the benefits of lubrication injections, or viscosupplementation. Viscosupplements are doses of hyaluronic acid that are injected into the knee and into the synovial fluid. This is a relatively new form of treatment for knee OA. Viscosupplementation has become more popular and more widely accepted, and is being used to treat symptoms of mild to moderate OA of the knee. However, its level of effectiveness in pain relief varies from person to person.

People with OA of the knee have lower levels of hyaluronic acid in their synovial fluid. What fluid does remain in the joint is often thinner and less effective than fluid in healthy joints. It is not able to protect the cartilage and bone from grinding and damage as well as it once could.

For each dose of a viscosupplement, a doctor injects hyaluronic acid (also called hyaluron or hyaluronate) into the knee joint’s synovial fluid.

The additional hyaluronic acid fills the joint area and increases lubrication in the joint, making movement much easier. Researchers also think that the injection of hyaluronic acid may stimulate the body to produce more of its own hyaluronic acid, which will further cushion the joint and make the effects of the injections last longer.

Most viscosupplements come from birds—chickens. Hyaluronic acid is often made using sterilized rooster combs, the fleshy crown on top of a rooster’s head. People who have a known or suspected allergy to chicken, poultry, and eggs should avoid receiving viscosupplements derived from avian sources in order to avoid a potential allergic reaction. However, newer forms have been produced that do not come from avian sources.

Viscosupplementation is ideal for people who have mild to moderate OA of the knee. It may be especially useful for people who have not responded to other OA treatments, such as physical therapy, weight loss, pain relievers, and corticosteroid injections.

People with severe OA, especially those who have bone-to-bone contact in their knee joint, will likely not benefit from viscosupplement injections and will instead need more aggressive treatment, such as surgery or joint replacement.

The benefits of viscosupplementation injections are not immediate. Because the injections are given over time, you may begin to feel some benefit after the first injection, but the greatest benefit may not be felt until several weeks or maybe even months after your first injection. The injections may be repeated every six months if you receive a benefit from the initial series of injections.