In this interactive video experience, you will learn how osteoarthritis of the knee develops, the role of synovial fluid in the knee joint, and how advancements in injectable therapies can help reduce the symptoms of OA of the knee. Use the blue arrow keys to advance through the three levels of the experience, and click the play button to start each video.
Osteoarthritis of the Knee and the Role of Synovial Fluid
Osteoarthritis (OA) is the most common form of arthritis. It’s a frequent cause of pain and dysfunction in the knee, estimated to affect about one-quarter of American adults. Women are more prone to knee OA than men. Nevertheless, OA is the most common cause of knee pain among people over the age of 50. Both aging and obesity are risk factors for knee OA. OA is believed to result from natural aging processes rather than trauma or disease.
OA of the knee begins with changes in the synovial fluid surrounding the knee joint. This fluid provides cushioning and lubrication for the joint, while supplying 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. Flaking may occur, and inflammation develops, further eroding the integrity of the joint cartilage. White blood cells infiltrate the synovial sac, releasing inflammation-promoting proteins called cytokines. As inflammation escalates, joint cartilage deteriorates further, in a vicious cycle of protein degradation, pain, swelling, and inflammation.
Treating Osteoarthritis with Viscosupplements
Treatment with common anti-inflammatory drugs, such as aspirin, is standard therapy for mild osteoarthritis. 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. The physician may employ imaging technology, such as ultrasound, to guide precise placement of the needle. A small amount of compromised synovial fluid is first removed.
Using a second needle, the physician then injects an equivalent volume 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.
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, although not all patients experience symptomatic relief. Evidence suggests that hyaluronic acid injections may stimulate the body to produce more of its own hyaluronic acid. Although corticosteroid injections may provide fairly rapid inflammation relief, it may require several weeks before hyaluronic acid injections take effect.
Treating OA of the Knee
Injection of hyaluronic acid is a new option for patients with symptomatic knee osteoarthritis. This is a new technology that does not help all patients, but some patients do seem to have reduced pain. This is an appropriate treatment to try if lifestyle changes and traditional medical therapies have not relieved the pain of osteoarthritis in the knee.