Short answer. Nobody knows yet. The studies so far are small, and the large Australian trial designed to settle the question has not yet reported.
Evidence grade. Not enough evidence yet.
What it is
Stem cells are cells that can grow into other cell types. For knee arthritis they are usually taken from fat or bone marrow, either your own or a donor’s, processed in a laboratory and injected into the knee. The hope is that they calm the joint and help the cartilage repair itself. Private clinics offer these injections.
What the research shows
Small trials have compared stem cell injections with salt water or gel injections. Some found less pain in the stem cell group, and a few reported changes on MRI that might point to cartilage repair. When these trials are pooled, the result looks positive.1 The problem is the size and quality of the trials. Most had fewer than 50 people, used different types and doses of cells, and were run by groups with an interest in the result. Trials that small cannot tell a true effect from chance or from the placebo effect that follows any injection into a sore knee.
The trial built to answer the question is the SCUlpTOR trial, run in Sydney and Hobart. It enrolled 440 people with knee arthritis and compared donor stem cell injections with salt water injections over two years, with neither patients nor doctors knowing who had which. It measures pain and cartilage thickness on MRI.2 Until it reports, the honest grade is not enough evidence.
Risks and effort
The injections appear safe in the short term, with pain and swelling for a few days the usual problem. Taking fat or bone marrow to make the cells is a small procedure with its own small risks. Regulators in several countries have tightened the rules on how these cells can be made and advertised because of past problems with clinics overstating what the treatment can do.
What usually works instead
Exercise, weight loss and simple pain relief have good evidence and should come first. A cortisone injection can settle a flare. Knee replacement remains the reliable treatment for arthritis that limits daily life. See Osteoarthritis of the Knee and Does exercise work for knee arthritis?.
Questions people ask
Can stem cells regrow my cartilage?
No study has shown new cartilage that lasts. Some small trials report MRI changes, but these are hard to measure and have not been confirmed in a large trial.
The clinic showed me before and after scans. Is that proof?
No. Scans from a few patients chosen by the clinic do not show what happens to most people, and MRI changes do not always match how the knee feels. Only a trial with a comparison group can show whether a treatment works.
Is it better to use my own cells or donor cells?
Nobody knows. Both are being studied. Donor cells are easier to standardise, which is why the large Australian trial used them.
Should I wait for the trial results?
If you are thinking about paying for this treatment, yes. This page will be updated when the results are published.
References
- Wang J, Xue H, Shi M, Chen R. Mesenchymal stem cell-based therapy for osteoarthritis: a systematic review and meta-analysis of clinical outcomes and functional recovery. Front Cell Dev Biol. 2026;13:1746471. https://doi.org/10.3389/fcell.2025.1746471
- Liu X, Robbins S, Wang X, Virk S, Schuck K, Deveza LA, Oo WM, Carmichael K, Antony B, Eckstein F, Wirth W, Little C, Linklater J, Harris A, Humphries D, O’Connell R, Heller G, Buttel T, Lohmander S, Ding C, Hunter DJ. Efficacy and cost-effectiveness of Stem Cell injections for symptomatic relief and strUctural improvement in people with Tibiofemoral knee OsteoaRthritis: protocol for a randomised placebo-controlled trial (the SCUlpTOR trial). BMJ Open. 2021;11(11):e056382. https://doi.org/10.1136/bmjopen-2021-056382
Last reviewed 18 October 2026. Next review due when the SCUlpTOR results are published, or October 2027.