Viscosupplementation is a procedure in which a hyaluronic acid-based product is injected into an arthritic joint. Hyaluronic acid is a naturally occurring component of synovial fluid and articular cartilage. It is thought to play a role in joint lubrication and cartilage resilience, protecting the cartilage on a cellular level. Treatment typically consists of between three and five weekly injections into the affected joint. The effect of the treatment is quite variable. When it is successful, symptomatic improvement can last for up to a six months. Viscosupplementation is only recommended for patients for whom traditional non-operative treatment has been unsuccessful, and as an alternative to surgery. Our understanding of hyaluronic acid injections, including its exact mechanisms of action, are currently evolving.

What is hyaluronic acid?

Hyaluronic acid, also called hyaluronan or hyaluronate, is a non-sulfated glycosaminoglycan. It is one of the chief components of the extracellular matrix (the non-cellular component of cartilage that makes up the vast majority of articular cartilage). It has been estimated that the average 70kg (154 lbs) person has roughly 15 grams of hyaluronic acid in their body, one-third of which is turned over (degraded and synthesized) every day.Hyaluronic acid serves a variety of important functions throughout the body, including playing a multifaceted role in the mediation of several cellular and matrix events in the process of skin tissue repair, and maintaining joint function. Hyaluronic acid is a major component and one of two natural lubricants found to increase the viscosity of synovial fluid.  Synovial fluid is the thick gel-like substance responsible for cushioning joints and providing lubrication to reduce joint friction. Hyaluronic acid is also present in a membrane around each cell (chondrocyte) of articular cartilage, which covers the ends of bones in a joint, contributing to its resilience. Additionally, the molecular weight and concentration of the naturally occurring hyaluronic acid decreases with age and at an accelerated rate for patients with osteoarthritis, decreasing the lubrication and protection of the joint tissues.
Hyluronic acid has been used to treat osteoarthritis through a series of hyaluronic acid-based injections into the joint cavity. These injections are thought to supplement the viscosity of the joint fluid (viscosupplementation), lubricating and cushioning the joint and producing an analgesic effect. It has also been suggested that hyaluronic acid has some direct positive biochemical effect on the cartilage cells.

When are hyaluronic acid injections indicated?

Injection of hyaluronic acid may improve the symptoms associated with osteoarthritis, including pain, swelling, stiffness, and loss of motion. These symptoms are caused directly or indirectly by the breakdown and wear of the surface layer of cartilage and the loss of synovial fluid viscosity. Hyaluronic acid injection may be considered for patients with osteoarthritis (ex. ankle arthritis) for whom traditional nonsurgical management has proven ineffective. It may be offered either as an alternative to surgery, or for those patients who may not be candidates for surgery. The exact indications for viscosupplementation are still evolving.Unlike corticosteroids, which produce a non-specific dampening of the inflammatory response, hyaluronic acid injections act specifically on the joint. Viscosupplementaion was first developed as treatment for knee arthritis.  However, it has since been applied to both the ankle and shoulder - and could theoretically be applied to any other joint affected by osteoarthritis.  However, it is important to note that the FDA has only approved hyluronic acid injections as a treatment for osteoarthritis of the knee. Use of hyluronic acid injections in other joints is therefore considered "off label" use, although this practice appears to be widespread. The exact mechanism of action of hyluronic acid is unclear, although restoring and increasing the viscosity of the synovial fluid and directly strengthening the cartilage seems to be the most logical explanations.Like corticosteroids, hyaluronic acid injections do not work in the long term. The injected hyaluronic acid product stays within the joint space for anywhere from hours to days. Patients may see results for two months or four months or maybe even six months, but treatment does not change the underlying pathology. Although the procedure is in no way a cure, some patients may note long-term benefit because it may break the cycle of the arthritic pain. Patients with arthritis tend to limit their own joint movement because it is painful, but in doing so cause the muscles in the surrounding area to atrophy. This may have the effect of increasing their pain and further restricting their range of motion, thus continuing a pattern of decreased movement and increased pain. Although it does not address the underlying issue of the arthritis, for many patients viscosuplementaion may be a reasonable option.While many patients with osteoarthritis in the knee and ankle have noted positive results from hyaluronic acid injections, clinical studies of two hyaluronic acid products, hyaluronan and hylan G-F 20, have been equivocal and inconclusive. Because some placebo-controlled studies have cast doubt on its efficacy, it does not look to have been the cure-all panacea the medical community had hoped it would be.

How is the injection performed?

The injection is carried out in the doctor's office. The skin is sterilized prior to the injection (usually with betadine or alcohol) and the needle is injected into the involved joint. Oftentimes, due to the significant cost of the product, the procedure is performed under fluoroscopy to ensure that the needle is accurately positioned within the joint. Fluoroscopy is an imaging technique commonly used by physicians to obtain real-time moving images of the internal structures of a patient, through the use of an x-ray source and a fluorescent screen. If effusion is present, aspiration of the joint is recommended before the injection to prevent dilution of the injected hyaluronic acid. Often, a local topical anesthetic or a small injection of lidocaine may be applied first to provide short term numbing of the area. The anesthetic typically wears off within a few hours. Injections are relatively easy to administer, take effect more rapidly than traditional anti-inflammatory medications, and avoid side effects that often accompany them, such stomach irritation.Three hyaluronic acid products are currently available in the United States: naturally occurring hyaluronan (Hyalgan), sodium hyaluronate (Supartz), and synthetic hylan G-F 20 (Synvisc). The recommended injection schedule is one injection per week for five weeks for Hyalgan and Supartz, and one injection per week for three weeks for Synvisc. Repeat courses of viscosupplementation can be performed after six months, if the patients experience positive results.Because hyaluronic acid has contradictory duo-functions in the inflammatory process, playing a significant role in both its stimulation and moderation, it is common for patients to experience worsening symptoms over the next few days before noticing improvement. Patients should avoid any strenuous activities or prolonged (more than 1 hour) weight-bearing activities (such as jogging or tennis) for 48 hours following the injection.Oral use of hyaluronan has recently been suggested, and its effectiveness is currently being tested in preliminary clinical studies.

Potential Risks of Hyaluronic Acid Injections

Potential complications include risk of infection at the injection site, which could be very serious if it goes directly into the ankle joint. Besides the inherent danger, history of infection is a contraindication for certain procedures like ankle replacement. Other reasons patients think twice about the procedure are the expense, and the short term nature of the effects. Results vary from person to person and typically last from two to six months, but in no case is the injection a longterm cure. Some people have inflammatory reactions to the injection, due to hyaluronic acids complex role in the inflammatory process, and find that in the short term, they feel even worse off than before.The cost of hyaluronic acid is significant. According to the 1999 issue of the Red Book, a pharmacological reference guide of pricing and product information, the average wholesale price for five vials of Hyalgan is $661.00, and a package of three prefilled syringes of Synvisc is $620.00. Today, the cost of Supartz is between $300 and $400. The United States Food and Drug Administration classifies viscosupplements as a device, not a drug. Medicare and private insurance typically reimburse the cost of devices and procedures that are medically necessary to treat your condition, and are used according to the labeled uses approved by the FDA. However, the FDA has currently only approved injections for the knee, although they are being studied for use in joints of the shoulder, hip, and ankle.

Edited October 10th, 2015

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