Stem cells for knee arthritis: what the evidence shows
Patients ask us about this more than anything else. So here is a straight account of what the research has found, what it has not, and what Health Canada and the FDA actually say about whether you can get it. Every number is sourced. Where the evidence is genuinely encouraging, we say so.
First, the word means several different things
A great deal of confusion starts here. “Stem cell injection” is used to describe treatments that are not the same as each other, are not made the same way, and do not have the same evidence behind them.
| What it is called | Where it comes from |
|---|---|
| Bone marrow aspirate concentrate (BMAC) | Drawn from your own pelvis, then concentrated |
| Stromal vascular fraction (SVF) | Processed from your own fat |
| Umbilical cord or cord blood products | Donor birth tissue |
| Amniotic fluid products | Donor birth tissue |
| Exosomes | Cell-derived particles, not cells |
| Platelet-rich plasma (PRP) | Your own blood, spun down. Not a stem cell treatment at all. |
PRP is frequently sold alongside these and frequently confused with them. It contains platelets and growth factors, not stem cells.
The distinction matters for a practical reason: when a clinic quotes you a study, the product in that study is frequently not the product being offered to you. Trials use defined cell types at defined doses; commercial off-the-shelf products vary, and Health Canada names BMAC, stromal vascular fraction and adipose-derived stem cells specifically as the offerings it sees in for-profit clinics.7
The largest trial to date
The MILES trial was published in Nature Medicine in 2023. It was a phase 2/3 randomised, multicentre, four-arm trial in 480 patients with knee osteoarthritis. It compared three different cell therapies — bone marrow aspirate concentrate, umbilical cord tissue mesenchymal stromal cells, and stromal vascular fraction — against a corticosteroid injection.1
That is the finding. Three different cell products, 480 patients, and at twelve months none of them separated from a steroid shot costing a small fraction of the price.1
It does not say the treatments do nothing. Patients in all four arms improved. It says the cell therapies did not beat a corticosteroid injection at one year on knee pain. It also used specific products at specific doses, and a different product at a different dose could behave differently.
The wider evidence is genuinely mixed
It would be dishonest to stop at one trial. Reviewing the field properly, there is encouraging data as well.
A 2025 meta-analysis pooling six randomised trials in 300 patients found a moderate to large effect on WOMAC scores at twelve months following a single mesenchymal stem cell injection.2 Between 2000 and 2025 there have been more than 200 registered clinical trials of stem cell therapies for osteoarthritis worldwide.8 This is a field with serious scientific investment behind it, and dose, cell source and preparation method are all still being studied as reasons the trials disagree with each other.
Against that, a 2025 systematic review set out to measure how much of the improvement patients report after these injections is attributable to contextual and placebo effects rather than to the cells themselves.3 That the question is being formally asked, in a registered review across five databases, tells you something about where the field currently stands.
And the professional bodies have not moved. The Arthroscopy Association of Canada’s position is that stem cell and bone marrow concentrate injections should be limited to registered controlled trials, and cannot be recommended in routine clinical practice until further evidence becomes available.6
The evidence is real but unsettled. Trials use different cells, different doses and different preparation methods, which makes them hard to compare and makes it hard to know whether any individual clinic’s product resembles the one that was studied. That is a description of an unsettled field, not a verdict on any clinic.
What about PRP?
PRP is cheaper, uses your own blood, and is often the first thing offered.
In a double-blind randomised trial, patients received either PRP, plasma alone, or saline — two ultrasound-guided injections, two weeks apart. At 24 weeks there was no significant difference between the three groups in pain or function. All three improved. The PRP group reported adverse events more often than either comparison group, mostly a mild temporary increase in pain.4
That is one trial of 62 patients, and the wider PRP literature is larger and more mixed than that. But it is a well-designed trial with a saline control, and saline held its own.
Can you get stem cell injections in Canada?
Not for a knee, and this surprises most people who ask us.
Health Canada’s published position is that all cell therapies are drugs under the Food and Drugs Act. They must be authorised before they can be offered to Canadians — and that applies even when the cells come from your own body.7
To date Health Canada has authorised three: Prochymal, for graft-versus-host disease, and two cell-based gene therapies for certain cancers. None of them is for joints. Everything else remains experimental, and may be given to Canadians only inside a clinical trial that Health Canada has authorised.7
That was 2019. CBC reported on clinics in Kingston and Toronto complying with the orders; the Toronto clinic had performed close to a hundred knee and hip treatments at around $4,000 each.9
Health Canada has also said it will engage provincial regulators, including the physician colleges, where it finds non-compliance.9
Some clinics have argued that because the cells are the patient’s own and are only minimally processed, the rules should not apply. Health Canada’s position paper was published specifically to address that argument. If you are offered this treatment in Canada, the question worth asking is whether it is being provided inside an authorised clinical trial.7
And in the United States
This is the part patients are most often surprised by, and it is not a matter of interpretation. The FDA’s published consumer alert states that none of these products have been approved for the treatment of any orthopedic condition, including knee pain and osteoarthritis.5
The only stem cell products currently approved in the United States are blood-forming stem cells derived from umbilical cord blood, approved for blood disorders such as leukaemia. Not for joints.5
The FDA also notes it has received reports of serious harm from unapproved regenerative products, including infections, tumour formation and blindness — across all uses, not specifically knees.5
These two phrases appear in clinic marketing and mean different things. Compliant describes operating within a regulatory framework. Approved means a product has completed the full approval process including phase III trials. If a clinic uses the first phrase, it is worth asking directly which one applies.
What it costs
Wherever it is offered, it is paid out of pocket. No public system and no insurer covers it for knee osteoarthritis, because it remains investigational.
For a Canadian reference point: the Toronto clinic CBC reported on in 2019 charged around $4,000 for the full course.9 US clinic pricing spans a wide range and is often sold as a package of more than one injection, so the figure quoted first is not always the total.
Questions worth asking any clinic
Including ours. These are the questions we would want a member of our own family to ask.
- Exactly which product and what dose? Then ask for the peer-reviewed trial of that specific product at that specific dose.
- Is it approved for knees where I live? A direct question with a direct answer.
- How many injections, over what period, at what total cost? Ask for the full figure, not the first one.
- What happens if it does not work? Ask before you pay, not after.
- What does the negative evidence say? Any clinic that cannot name the trials that did not go their way has not read the field.
Where our treatment differs
We do not offer stem cell or PRP injections. We offer a single injection of a permanent hydrogel implant, which is a different treatment with a different evidence base — a randomised controlled trial with published follow-up out to five years, and observational follow-up out to ten.
It is not a cure, it does not regrow cartilage, and it does not work for everyone. We set all of that out, with the studies and their limits, on our research page.
We have also written up whether knee cartilage can actually be regrown, since that is the other thing patients ask us about — where cartilage repair genuinely works, and what happened in the one trial where a drug measurably grew cartilage in arthritic knees. That is on our cartilage regeneration page.
If you are weighing your options, read all three. That is the point of publishing them.
Sources
- Cell-based versus corticosteroid injections for knee pain in osteoarthritis: a randomized phase 3 trial (MILES). Nature Medicine 2023. Four-arm randomised trial, 480 patients. Read the trial
- Efficacy of a single intra-articular injection of mesenchymal stem cells for knee osteoarthritis: a dose-focused meta-analysis of randomized controlled trials. Journal of Orthopaedic Surgery and Research 2025. Six RCTs, 300 patients. Read the paper
- Contextual effects of mesenchymal stem cell injections for knee osteoarthritis: systematic review and meta-analysis of randomized controlled trials. Frontiers in Medicine 2025. DOI 10.3389/fmed.2025.1636181. Read the paper
- Efficacy of platelet-rich plasma and plasma for symptomatic treatment of knee osteoarthritis: a double-blinded placebo-controlled randomized clinical trial. BMC Musculoskeletal Disorders 2021. 62 patients; PRP, plasma and saline compared. Read the trial
- US Food and Drug Administration. Consumer Alert on Regenerative Medicine Products Including Stem Cells and Exosomes. Read the alert
- Arthroscopy Association of Canada position on stem cell and bone marrow concentrate injections for osteoarthritis and musculoskeletal injury, as reported in a review of the Canadian evidence and regulatory landscape. Read the review
- Health Canada. Advisory on the potential health risks associated with unauthorized cell therapy treatments such as stem cell therapy. Read the advisory
- Registry analysis of interventional clinical trials of stem cell therapies for osteoarthritis worldwide, 2000 to 2025.
- CBC News. Health Canada orders private clinics to stop offering certain stem cell therapies, July 2019, including reporting on clinics in Kingston and Toronto and the fees charged. Read the report
This page is general information about treatments for knee osteoarthritis. It is not a diagnosis and it is not medical advice about your knee. It describes what the published research reports; it is not a comment on any individual clinic or practitioner. Whether any treatment is right for you depends on what is happening inside your joint, which is what an assessment is for.