Q. I heard there's this goop that you can get injected into your knee that can ease pain. True?

Yes. The goop is hyaluronan, a thick lubricant and shock absorber in joint fluid. Hyaluronan injections, also called viscosupplements, are given to people with osteoarthritis.

Viscosupplementation began in Japan and Italy in 1987, in Canada in 1992, in Europe in 1995 and in the United States in 1997.

Some anatomy. The knee, which is the largest joint in the body, is made up of the thighbone (femur), shin bone (tibia) and the kneecap (patella). Surfaces of this joint are covered with cartilage, a smooth substance that cushions the bones and enables them to move easily. The lateral meniscus and medial meniscus are pads of cartilage that further cushion the joint, acting as shock absorbers between the bones.

In addition, surfaces of the knee are covered by a thin, smooth tissue liner called the synovial membrane. This membrane releases fluid that lubricates the knee and reduces friction.

Osteoarthritis is a degenerative joint disease which primarily affects cartilage. The cartilage erodes and the synovial fluid loses its ability to lubricate the joint. This breakdown causes pain, stiffness and limited range of motion.

Hyaluronan is injected into the knee to improve lubrication and reduce the symptoms of osteoarthritis. There are several versions of hyaluronan injections for osteoarthritis in knees. These include: Euflexxa, Hyalgan, Orthovisc, Supartz, Synvisc and Nuflexxa.

Hyaluronan injections are recommended when conservative treatments medications, physical therapy, heat/cold aren't working. The injections produce their best results if the patient is in the early stages of osteoarthritis. Possible side effects of these injections include joint swelling and pain.

The course of treatment depends upon the drugs used. The injections are usually given weekly. Synvisc-One is a single injection viscosupplement.

In an analysis of eight hyaluronan trials involving 971 patients, outcomes in patients treated with hyaluronan were superior to outcomes in patients treated with placebo. The most significant pain relief occurred 8 to 12 weeks after the first injection for most patients.

Studies showed that Synvisc and Hyalgan provide pain relief from knee osteoarthritis for up to six months. Supartz was shown in studies to provide pain relief for up to 4 1/2 months after the fifth injection. Patients may be able to repeat the course of treatment with hyaluronan injections.

However, a recent study out of Switzerland indicates that the injections don't work. According to the researchers, the effect on pain was minimal, and the injections had no effect on functioning.

In addition, the research in Switzerland suggested the injections could cause gastrointestinal and cardiovascular problems and other harmful side effects.

The researchers reviewed 89 studies that compared injections with either a placebo treatment or no treatment. In all, the studies involved more than 12,000 adults aged 50 to 72.

The authors pointed out several study limitations. They said the methodology of some of the studies was flawed, the overall quality was generally low, and many provided no information on safety.

Medicare and most insurance companies now cover viscosupplementation with restrictions.

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