Knee osteoarthritis is a complex disease that affects the whole joint, including bone, cartilage, ligaments and muscles. Osteoarthritis is a common cause of pain and movement difficulty, affecting 8.3% of people in Australia.

When pain persists, many people look for quick, convenient options, such as injections. Clinics offer several types of knee injections, including:

• corticosteroids
• hyaluronic acid
• platelet-rich plasma
• stem cells.

Some are heavily marketed with promises to “repair” or “regenerate” the joint. But what does the evidence actually say about these claims, or the ability of knee injections to reduce pain and improve mobility?

Corticosteroid injections

Corticosteroids are anti-inflammatory medications that can reduce pain and swelling in the joint.

They are conditionally recommended in guidelines because they can be helpful for short-term relief, particularly during a flare-up.

However, a 2024 systematic review found meaningful benefits only in the first few weeks. They lose their effectiveness after about six weeks.

There are also some concerns about repeated use. One trial found corticosteroid injections every three months over two years did not improve pain, and were associated with greater cartilage loss than a placebo.

For this reason, guidelines recommend using corticosteroid injections cautiously for short-term relief rather than ongoing treatment.

Hyaluronic acid injections

Hyaluronic acid is a substance naturally found in joint fluid. These injections aim to improve “lubrication” or “shock absorption” within the joint.

While this may sound promising, a large systematic review found the benefits are small and unlikely to be meaningful. There was also a higher risk of serious adverse events compared to placebo.

Because of this, guidelines do not recommend these injections for knee osteoarthritis.

Platelet-rich plasma injections

Platelet-rich plasma (PRP) injections use a person’s own blood, which is processed to concentrate platelets and then injected into the joint.

As platelets contain growth factors, chemicals that help signal the body to heal tissue, the idea is they may help repair the joint.

These injections are widely marketed but expensive: typically A$300–$900 per injection, or up to $2,700 for a course of three injections.

It’s generally considered safe, with the main risks being those of any joint injection, such as infection.

Some systematic reviews report benefits, but findings vary considerably, with other reviews finding weak effects when compared to placebo. Some larger, rigorous trials show little or no benefit. So the overall picture is mixed.

A key problem is lack of standardisation, with different clinics using different concentrations and methods. This makes it hard to know what works for pain and mobility. However there is no good evidence platelet-rich plasma injections repairs or regrows joint cartilage.

Current guidelines do not recommend platelet-rich plasma injections, though this may change with more high-quality research.

Stem cell injections

Stem cells are often promoted as a way to regenerate damaged tissue. They can be taken from a person’s own body, or prepared from donor cells in a laboratory. But despite the hype, the evidence is still very limited.

A recent Cochrane review found stem cell injections may provide small improvements in pain and function. But the results were uncertain and from low-quality evidence.

There is also a small risk of adverse events, including infection.

So far, no published studies have evaluated whether they repair cartilage or change osteoarthritis progression.

Guidelines currently recommend against their use due to limited evidence, high costs (often $5,000 or more per injection), and regulatory concerns about how they are made and prepared, and how they are marketed to patients.

More high-quality research is underway, including a clinical trial in Australia measuring whether they can slow osteoarthritis progression.

Why isn’t the evidence clearer?

Many studies are small or low quality.

Placebo effects are also particularly large with injections, meaning studies without placebo controls may overestimate the benefits.

For platelet-rich plasma injections and stem cells, variable methods used across clinics further complicates interpretation.

So what can I try for my knee osteoarthritis?

Treatments that are recommended include:

• any type of exercise
• weight loss, if appropriate
• over-the-counter medications, such as short-term use of anti-inflammatories.

These approaches are backed by high-quality evidence, are generally safe, and are less expensive than injections.

What if I want to try an injection?

If other recommended treatments haven’t helped and you decide to try an injection without a strong evidence base, such as platelet-rich plasma injections, there are a few things worth keeping in mind.

First, weigh up the costs, risks and benefits. All injections carry a small risk of joint infection, so it’s not completely risk-free.

It’s also worth knowing it’s unclear exactly how these injections work.

Some of the benefits you may experience could be related to placebo effects rather than the injection itself.

If you do go ahead, any reduction in pain should become apparent within six weeks, or sooner with corticosteroids.

Bottom line

Most injections offer limited or uncertain long-term benefit for knee osteoarthritis. Despite the marketing, there is no good evidence any injection can repair the joint.

A corticosteroid injection can be a reasonable short-term option during a bad pain flare. There may be some evidence to support platelet-rich plasma injections, but preparations aren’t standardised. Hyaluronic acid and stem cell injections are not currently recommended.

Before paying for any injection, consider what the evidence says and whether your time and money might be better spent on options such as exercise and weight loss, which have higher-quality evidence and additional health benefits beyond the knee.

Belinda Lawford, Senior Research Fellow in Physiotherapy, The University of Melbourne; Kim Bennell, Professor of Physiotherapy, The University of Melbourne, and Travis Haber, Postdoctoral Research Fellow in Physiotherapy, The University of Melbourne

This article is republished from The Conversation under a Creative Commons license. Read the original article.