Q. My husband is 44 years old and weighs 65kg. He is 1.63m tall. He has had arthritis of the knee for about four years. Every time the pain comes, he needs to go to the doctor for a suplasyn (2ml) injection on his knee. The injection, which costs about $200, usually lasts for six months.

Is this injection safe, and are there long-term side-effects or better treatment? Is knee replacement recommended?

A You are referring to one form of joint injection known as hyaluronic acid injection. Different forms are derived from different sources, but they all have similar effects.

In this case, it provides an effect known as visco-supplementation, which supplements the normal synovial fluid found inside knee joints, particularly when the body's natural synovial fluid is lacking or of poor quality such as in osteoarthritis.

The injection improves lubrication in the knee joint and reduces friction. This type of injection is not a steroid, and is generally safe with few side-effects. However, no procedure is completely risk-free. All injections into the knee joint carry a very low risk of infection of the joint.

It is possible that the knee may react to the injection, leading to more pain and swelling. This is usually temporary and will subside, but if someone receiving the injection turns out to be allergic to hyaluronic acid, the adverse effect may be more severe.

It is also possible that repeated courses of hyaluronic acid injection will increase the risk of a reaction.

Whether there are better forms of treatment depends on what condition your husband is suffering from in the knee joint. At the age of 44, he seems a bit young to develop osteoarthritis of the knee, unless previous injury or inborn deformity predisposed him to it.

Although hyaluronic injections can be helpful to some people with early osteoarthritis, with more advanced arthritis, the benefit lessens.

Your husband is generally considered very young to have a knee replacement. Most specialists would be very cautious about doing one unless his condition really requires it.

This article was first published in Mind Your Body, The Straits Times on August 6, 2008.