Viscosupplementation: Knee Injections for Osteoarthritis

Introduction

You may have heard about some new knee injections for osteoarthritis, such as viscosupplementation. You may have wondered what they are - and if they would help you. We'll start with the basics.

Hyaluronan is a carbohydrate that is in the fluid inside your joints. The medical abbreviation for hyaluronan is HA. High levels of HA in the joint fluid make it viscous - thick and sticky. So the fluid acts like a lubricant and a shock absorber. This protects your knee from damage during everyday stress -- like walking, running and jumping.

But if you have osteoarthritis, the level of HA in your joint fluid is lower. So the joint fluid is thinner and less sticky - and less protected.

Hyluronan has been manufactured in the laboratory. Three slightly different types are available: Synvisc, Hyalgan and Artzal. They are marketed as treatment for mild to moderate knee osteoarthritis. Because they are thick, jelly-like substances, the treatment is called viscosupplementation.

Treatment involves a series of three to five weekly injections into the knee joint. It may take up to two months to see the full effect of treatment. The benefits of treatment vary from person to person - sometimes six months, sometimes longer.

At this time, HA has only been approved by the FDA for use in the knee. However, researchers are looking at it for use in other joints, such as the hip, shoulder, jaw, low back, and base of the thumb.

How Does HA work?

At first, doctors thought HA worked simply by replacing the missing HA in osteoarthritic joints - like putting new oil into a rusted ball bearing. However, research showed that injected HA only stayed in the joint about a week. Then it is absorbed by the body.

So why HA improves pain in some patients is unknown. It may stimulate your body to make more or your own natural HA. Or it may act as a scavenger, mopping up destructive inflammatory products in your damaged joint. And it may slow down inflammation that can lead to pain and further joint damage. We just don't know yet.

What are the main side-effects?

More than 5 million injections of HA have been given, and it has proven remarkably safe. Typically, less than 3% of patients have had minor local reactions at the injection site with the first injection. The risk of such local reaction increases with repeated injections. Any knee swelling is easily treated with corticosteroid medications. Only two people had serious - potentially life-threatening side effects, which were treated immediately and resolved without further problems.

Any injection into a joint brings a risk of infection. However, this is exceedingly uncommon when the injection is performed by an experienced physician under sterile conditions. (The estimate of infection due to a corticosteroid injection is 1/ 17,000-1/50,000.) Existing research shows no increased risk of joint infection with the use of HA.

Here's an important statistic. The best way to estimate risk is to look at randomized controlled trials. Half of the people are injected with the real medication and half get a fake or "placebo." In most such trials, there was no difference in side effects between HA and placebo injections.

Does it matter which product is used?

We don't know. No research study has compared all three products head to head. Only one carefully done study - the researchers didn't know who was getting what - compared two of them (Artzal and Synvisc). It showed no difference in effectiveness between the two.

Does HA really work?

That's controversial. Some people who have had the shots sing their praises. Some say they did nothing. But those are only individual stories. Doctors call that "anecdotal evidence." Doctors look for big studies and "statistical evidence" - data. And the data on HA in knee OA is controversial.

Yes, many studies have found that HA improves pain and function in some people with mild to moderate knee OA[1],[2] But does it work better than corticosteroid injections? Or better than pills such as non-steroidal anti-inflammatory drugs (such as ibuprofen or COX-2 inhibitors or acetaminophen), or even placebo injections?[3],[4]

For example, one study looked at people who had had joint injections of either HA or steroids. A year later, those who had the HA still had less pain. But another study found no difference between steroids and HA six months after the injections[5]. In fact, a number of osteoarthritis experts do not find existing data compelling enough to promote the use of HA in knee OA[6].

We don't know whether their disagreements are due to flaws in study design, differences in interpretation of study results, or actual differences in the effectiveness of HA.

However, HA is a reasonable treatment option for some patients who have not had good benefit from other conservative therapies - because of:

• the "data" available,
• the terrible impact osteoarthritis can have on your life, and
• the very low risk of HA side-effects.

Can HA change the course of osteoarthritis?

Cartilage is the rubbery cushion that protects bone ends - where they meet in joints. In osteoarthritis, that cushion breaks down. In some research, animals given HA had less severe cartilage damage after trauma. In others they did not. The difference may have been a result of timing. In humans, some studies showed HA can improve or halt cartilage destruction. But this is very early research - and they were not rigorous, randomized, controlled trials. So the answer is, we don't know yet.

Who might benefit from HA?

Anyone who had symptoms of osteoarthritis should first have appropriate physical therapy, and try oral medications such as non-steroidal anti-inflammatory drugs, as prescribed by your doctor. If this approach does not work, your doctor may recommend corticosteroid injections into the joint. If you still need further help, other options will be considered.

Research still has not identified who can best benefit from HA. However, we do know that those with severe osteoarthritis are excluded from research studies. Most researchers feel HA is not effective in patients with end-stage joint destruction.

Among the other options is a trial of HA. However, cost is also an important factor. Each course of HA costs hundreds of dollars. Although most insurance policies do cover HA, check with your pharmacy coverage before starting a course of therapy.

If one brand of HA does not work, there are no data to suggest that it is worth trying another.