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Think about intra-articular therapy for osteoarthritis

EC Huskisson
MD FRCP
Consultant Rheumatologist
London

Easy things to do for osteoarthritic knees include NSAIDs and analgesics, quadriceps exercises, diet and supplements like glucosamine and chondroitin sulphate, which are of proven efficacy. In advanced disease, replacements will be the answer. The big challenge is the patient who hasn't done particularly well with these simple things but doesn't need replacements. It is for this patient that intra-articular therapy is worth considering.
It is not difficult to inject a knee, although studies have shown that up to 50% of injections by so-called experts do not reach the joint cavity. Professors of rheumatology are said to be the worst! The procedure requires a no-touch technique. A sterile needle is used to draw up the injection material and another to inject the joint. Nothing and no-one touches the needle. The skin must be cleaned and the environment must also be clean, but it is not necessary or desirable to use an operating theatre.
 
Studies suggest that steroids injected into an osteoarthritic knee have only a transient benefit. They are very useful in small joints like the first carpo-metacarpal joint at the base of the thumb and the metatarsophalangeal joint of the big toe, where the benefits are often prolonged. They are also the treatment of choice for pseudogout, which often complicates osteoarthritis, and for inflammatory episodes of osteoarthritis, which may be caused by crystal deposition. It is not unreasonable to try a steroid injection using a long-acting preparation like triamcinolone, especially for acute exacerbations.

Hyaluronic acid
Three to five intra-articular injections of hyaluronic acid given at weekly intervals into an osteoarthritic knee will give relief of symptoms lasting for six months or more. Studies show that intra-articular placebo given in this way is very effective but hyaluronic acid is more effective.

Why it works
Synovial fluid is viscous because it contains hyaluronic acid, the same material that makes the aqueous humour of the eye viscous and also the material that moisturises the skin of expensive ladies. Hyaluronic acid in synovial fluid has a viscosity of 5-6 million Daltons. In osteoarthritis, the fluid is less viscous with hyaluronic acid of between 0.5-3 million Daltons. It is even less viscous in rheumatoid arthritis. Injection of hyaluronic acid improves synovial fluid viscosity, although this may not explain the relief of symptoms. Hyaluronic acid injections stay in the joint for only days (up to one week with Synvisc), but they may teach the synovial membrane to make better quality hyaluronic acid itself.

What is the cost and what is the risk?
Hyaluronic acid is expensive, but so are the pain and immobility of an osteoarthritic knee. It is said that one in 10,000 intra-articular injections cause infection. Hyaluronic acid injections occasionally cause an inflammatory reaction in the joint, possibly because the material has been injected into soft tissue rather than the joint space. This occurs after 2% of Synvisc injections. But unlike NSAIDs, hyaluronic acid will not upset the stomach or cause a gastric bleed - worth remembering for the vulnerable elderly or the all-too-common patient who does not seem to be able to take anything by mouth and won't take anything by suppository.

Which preparation?
It is difficult to demonstrate the difference between hyaluronic acid and placebo in trials because placebo is so effective; it would require enormous numbers of patients to show differences between preparations of hyaluronic acid. No such differences have been shown. Whether a higher molecular weight means more or less efficacy and whether a synthetic preparation like Ostenil causes fewer reactions than those which come from chickens (Hyalgan and Synvise), we just don't know.

Conclusion
Think about intra-articular hyaluronic acid for the osteoarthritic knee that has failed to respond to simple treatments but does not need replacement. It is a useful extra option for the relief of a very common problem.

Further reading
Huskisson EC, Donnelly S. Hyaluronic acid in the treatment of osteoarthritis of the knee. Rheumatology 1999;38:602-7.