The idea behind viscosupplementation is the injection of a lubricant in the joint. It does not help cartilage growth and it does not reverse the disease.

This lubricant is a derivative of hyaluronic acid, a natural lubricant in joints. There can be organic (Synvisc) and synthetic (Orthovisc) variants of this. The organic variants are derived from chicken combs whereas the synthetic ones derive from a bacterial based manufacture process. The synthetic ones may therefore have theoretical advantage in reducing the risk of allergic reactions.

Most administrations involve single injections of about 6 ml of fluid into the knee. The procedure is a sterile process. Usually fluid is aspirated from the knee before injection. This abnormal fluid contains pain causing hormones within them and may itself reduce pain. The procedure is featured below.

In practice Synvisc may not actually be all that efficacious. In the carefully selected patient it may give benefit in about 60 to 70% of patients and the results may last between 6 to 9 months. Repeated injections after that result in progressively shorter periods of relief. Worse still the exposure of a patient to the agent can sensitize the patient such that the next injection can result in severe inflammation in the knee. This pseudo-infection can be distressing and lead to avoidable further treatment and even surgery. Chicken protein allergy in particular may be present in the patient and unrecognised and result in a severe allergic reaction. Many patients do develop warmth and swelling in the knee after the injection even without known allergies.

In my practice viscosupplementation is generally provided selectively to older patients who are not candidates for surgery and with significant arthritis. Cost should be borne in mind though. Three injections can cost the price of a knee replacement prosthesis.

Techniques of injection into the knee