More than 500 million people around the world live with osteoarthritis^[1]. The knee is affected more often than any other joint, with symptoms (such as pain, stiffness and reduced movement) affecting work, sleep, sport and daily activities^[2].

Knee osteoarthritis is often thought of as thinning of the protective layer of cartilage within the joint. But we now understand it affects all the structures of the joint, including the bones, muscles and nerve endings.

While there are things that can be done to manage^[3] the symptoms of knee osteoarthritis, there is no cure, and many people experience persistent pain. As a result, an opportunity exists for as yet unproven treatments^[4] to enter the market, often before regulatory safeguards can be put in place.

Stem cell injections are one such treatment. A new review^[5] my colleagues and I published this week finds that evidence of their benefits and harms remains elusive.

Stem cell treatments

Stem cells are already established as treatments for some diseases – mostly disorders of the blood^[6], bone marrow or immune system – which has led to suggestions they could be used for a much wider array of conditions.

Stem cells have been touted as promising treatments for osteoarthritis because they have special properties which allow them to replicate and develop into the mature healthy cells that make up our body’s organs and other tissues, including cartilage.

Stem cell treatments for osteoarthritis generally involve taking a sample of tissue^[7] from a site that is rich in stem cells (such as bone marrow or fat), treating it to increase the number of stem cells, then injecting it into the joint.

The hope is that if the right type of stem cells can be introduced into an osteoarthritic joint in the right way and at the right time, they may help to repair damaged structures in the joint, or have other effects such as reducing inflammation.

But no matter how convincing the theory, we need good evidence for effectiveness and safety before a new therapy is adopted into practice.

Stem cells have been touted as promising treatments for osteoarthritis. But what does the evidence say? crystal light/Shutterstock^[8]

Stem cell injections have not been approved by Australia’s Therapeutic Goods Administration^[9] for the treatment of osteoarthritis. Nonetheless, some clinics in Australia and around the world still offer them.

Because of the regulatory restrictions, we don’t have reliable numbers on how many procedures are being done.

They’re not covered by Medicare, so the procedure can cost the consumer thousands of dollars.

And, as with any invasive procedure, both the harvest of stem cells^[10] and the joint injection procedure may carry the potential for harm, such as infection.

What we found

Our new review^[11], published by the independent, international group the Cochrane Collaboration, looks at all 25 randomised trials of stem cell injections for knee osteoarthritis that have been conducted worldwide to date. Collectively, these studies involved 1,341 participants.

We found stem cell injections may slightly improve pain and function compared with a placebo injection, but the size of the improvement may be too small for the patient to notice.

The evidence isn’t strong enough to determine whether there is any improvement in quality of life following a stem cell injection, whether cartilage regrows, or to estimate the risk of harm.

This means we can’t confidently say yet whether any improvement that might follow a stem cell injection is worth the risk (or the cost).

Osteoarthritis of the knee is the most common type of osteoarthritis. michaelheim/Shutterstock^[12]

Hope or hype?

It’s not surprising we invest hope in finding a transformative treatment for such a common and disabling condition. Belief in the benefits of stem cells is widespread – more than three-quarters of Americans^[13] believe stem cells can relieve arthritis pain and more than half believe this treatment to be curative.

But what happens if a new treatment is introduced to practice before it has been clearly proven to be safe and effective?

The use of an unproven, invasive therapy is not just associated with the risks of the intervention itself. Even if the treatment were harmless, there is the risk of unnecessary cost, inconvenience, and a missed opportunity for the patient to use existing therapies that are known to be effective.

What’s more, if we need to play catch-up to try to establish an evidence base for a treatment that’s already in practice, we risk diverting scarce research resources towards a therapy that may not prove to be effective, simply because the genie is out of the bottle.

There are some ways to manage the symptoms of knee osteoarthritis. PeopleImages.com - Yuri A/Shutterstock^[14]

Working towards a clearer answer

Several more large clinical trials^[15] are currently underway, and should increase our understanding of whether stem cell injections are safe and effective for knee osteoarthritis.

Our review incorporates “living evidence^[16]”. This means we will continue to add the results of new trials as soon as they’re published, so the review is always up to date, and offers a comprehensive and trustworthy summary to help people with osteoarthritis and their health-care providers to make informed decisions.

In the meantime, there are a number of evidence-based treatment options^[17]. Non-drug treatments such as physiotherapy, regular exercise, maintaining a healthy weight, and cognitive behavioural therapy can be more effective than you think. Anti-inflammatory and pain medications can also play a supporting role.

Importantly, it’s not inevitable that osteoarthritic joints get worse with time. So, even though joint replacement surgery^[18] is often highly effective, it’s the last resort and fortunately, many people never need to take this step.

References

1. ^{^} live with osteoarthritis (www.thelancet.com)
2. ^{^} daily activities (www.aihw.gov.au)
3. ^{^} can be done to manage (www.safetyandquality.gov.au)
4. ^{^} as yet unproven treatments (www.rheuma.com.au)
5. ^{^} new review (www.cochranelibrary.com)
6. ^{^} mostly disorders of the blood (www.lymphoma.org.au)
7. ^{^} taking a sample of tissue (www.aboutstemcells.org)
8. ^{^} crystal light/Shutterstock (www.shutterstock.com)
9. ^{^} Therapeutic Goods Administration (www.tga.gov.au)
10. ^{^} harvest of stem cells (coroners.nsw.gov.au)
11. ^{^} new review (www.cochranelibrary.com)
12. ^{^} michaelheim/Shutterstock (www.shutterstock.com)
13. ^{^} three-quarters of Americans (www.arthroscopyjournal.org)
14. ^{^} PeopleImages.com - Yuri A/Shutterstock (www.shutterstock.com)
15. ^{^} clinical trials (anzctr.org.au)
16. ^{^} living evidence (www.cochrane.org)
17. ^{^} evidence-based treatment options (www.racgp.org.au)
18. ^{^} joint replacement surgery (aoanjrr.sahmri.com)