Osteoarthritis (OA) of the knee causes pain and joint dysfunction. It’s one of the most common forms of arthritis and affects about one-quarter of American adults. Most people with OA are over the age of 50. OA is believed to result from natural aging processes rather than trauma or disease.
Part 1 of 4: Causes
OA of the Knee and the Role of Synovial Fluid
OA of the knee begins with changes in the synovial fluid surrounding the knee joint. This fluid provides cushioning and lubrication for the joint. It also supplies nutrients to the articular cartilage at the ends of the bones of the leg. Joint cartilage has no blood supply of its own, so it relies on the synovial fluid to nourish and sustain it.
As the watertight synovial membrane shrinks and fluid content declines, pits and fissures develop in the protein structure of the cartilage. This can cause flaking of the bone or cartilage. White blood cells enter the synovial sac and release cytokines, or inflammation-promoting proteins.
As inflammation progresses, the joint cartilage deteriorates. This increased inflammation leads to pain, swelling, and reduced joint use, as seen in the following video.
Part 2 of 4: Causes
Treating Osteoarthritis with Viscosupplements
This next video shows how viscosupplement injections are made into the synovial sac.
Treatment with common anti-inflammatory drugs, like aspirin, is standard therapy for mild OA. But more advanced cases may warrant newer therapies such as viscosupplement injection. This modern approach involves inserting a small needle through the tissue of the knee into the synovial sac surrounding the joint.
Using a needle, your physician will first remove a small amount of existing synovial fluid. A second needle is then used to inject the same amount of sterile replacement fluid into the synovial sac. This fluid contains hyaluronic acid, a natural substance that helps lubricate the joint and nourish the proteins making up the cartilage of the joint. This replacement hyaluronic acid improves the viscosity, and thus the shock-absorbing capacity, of the synovial fluid. Injections may be given repeatedly, over the course of several weeks.
Part 3 of 4: Causes
Understanding Injectable Treatments for OA of the Knee
In the past, when anti-inflammatory drug therapy failed to provide adequate relief from the pain, swelling, and stiffness of knee OA, physicians often recommended corticosteroid injections. Performed in an outpatient setting, these injections are made directly into the knee joint, and can dramatically relieve inflammation for up to three weeks. They may not be effective for long-term use, however, as they do not prevent further deterioration of joint cartilage.
Newer viscosupplements feature injectable hyaluronic acid. This therapy helps reduce friction and improves the viscosity of the joint’s synovial fluid. It may provide pain relief for up to six months at a time, but this timeframe may not be the same for everyone. While corticosteroid injections may provide fairly rapid inflammation relief, it may require several weeks before hyaluronic acid injections take effect.
This video shows how viscosupplements work in comparison to corticosteroid injections.
Treating OA of the Knee
As a newer option for patients with OA of the knee, viscosupplements may be beneficial for those who have yet to find relief through traditional medical therapies, including corticosteroid injections, or lifestyle changes. The injection of hyaluronic acid may stimulate the body to produce more of its own hyaluronic acid, which can potentially lead to more long-term relief.