Quick answer: Published trials to date suggest that cell therapy for knee osteoarthritis is generally well tolerated, and several studies report improvements in pain and function. What current evidence has not established is that these therapies reliably regrow cartilage or change the course of osteoarthritis. Most published studies remain early phase, small and often lack control groups.
What Does the Evidence Show?
- Is it safe? Early trials consistently report good tolerability and few serious adverse events.
- Does pain improve? Several trials report improvement in pain and function, sometimes with dose-related differences.
- Does cartilage regrow? Not established.
- Is it disease-modifying? Not established.
- Are the trials large? Most are early Phase 1 studies, often involving only around 10–30 patients.
- Is it approved? Regulatory status varies by country. There is no globally approved disease-modifying cell therapy for knee osteoarthritis.
What Are Mesenchymal Stem Cells?
Mesenchymal stromal cells, often abbreviated as MSCs, can be isolated from several tissues including bone marrow, adipose tissue, umbilical cord and cord blood.
They are being studied in osteoarthritis because of their anti-inflammatory signalling and their potential to influence cartilage-forming activity.
An important distinction is that current scientific understanding suggests much of their effect inside the joint may be paracrine — meaning the cells release signalling molecules that influence the local environment — rather than the cells themselves becoming new cartilage. This matters when interpreting claims about “regeneration”.
What Did the Phase 1 Trials Find?
OSCA: Umbilical Cord Blood MSCs With Cartilage Matrix
A first-in-human, multicentre dose-escalation study involving 12 patients reported that the therapy was well tolerated with no dose-limiting toxicities. Pain and function scores improved, particularly in higher-dose groups. MRI findings suggested possible cartilage repair and joint preservation, although osteophyte progression was also observed in some patients.
Umbilical Cord MSC Dose Escalation
Another dose-escalation study found all tested doses to be safe and reported reductions in pain and inflammation by WOMAC score. Importantly, low and middle doses performed better than the highest dose, which was associated with local swelling and inflammation. More is not automatically better.
Repeated Allogeneic UC-MSC Injections
A Phase 1 study using repeated allogeneic umbilical cord-derived MSC injections reported no treatment-related structural joint damage. Cartilage remained stable in most participants, with modest improvement in tibial cartilage in a subset. Radiological changes did not consistently match clinical outcomes.
Why Does “Phase 1” Change How You Should Read These Results?
Phase 1 trials are designed primarily to answer whether a treatment is safe — not to prove whether it works.
Measures of pain, function or imaging change may still be collected, but these are usually secondary endpoints intended to help design later studies rather than establish effectiveness.
Sample sizes are also small. A study of 12 patients may help identify obvious toxicity, but it is not large enough to establish the size of a treatment effect reliably.
Many early studies also lack control groups. Osteoarthritis symptoms naturally fluctuate, and intra-articular injections can produce a placebo response. Without a comparison arm, improvement cannot always be separated from these effects.
Autologous or Allogeneic: Does the Cell Source Matter?
Autologous Cells
Autologous cells are taken from the patient’s own body, typically from bone marrow or adipose tissue. Their advantages include avoiding donor rejection and having a well-characterised safety profile. A limitation is that cell quantity and quality can vary with the patient’s age and health.
Allogeneic Cells
Allogeneic cells come from a donor, commonly umbilical cord or cord blood. They are studied because they may offer higher proliferative capacity, relatively low immunogenicity and more standardised preparation independent of the patient.
Several cord blood-derived products have been studied internationally. CARTISTEM, for example, is approved in South Korea for certain cartilage defects. Regulatory status varies substantially between countries, so approval in one jurisdiction should not be assumed to apply elsewhere.
What Would Strengthen the Evidence?
Larger randomised controlled trials are needed before stronger conclusions can be made. Important features include:
- A comparison arm — placebo or active control, to separate treatment effect from natural fluctuation and placebo response.
- Adequate sample size — large enough to establish effect size rather than safety alone.
- Longer follow-up — osteoarthritis progresses over years, so durability remains an important unanswered question.
- Agreed endpoints — including clearer agreement on the relative importance of structural imaging change versus patient-reported outcomes.
What Does This Mean If You Have Knee Osteoarthritis Now?
Based on current evidence, cell therapy is best understood as an option that may improve symptoms and function for some patients and has shown a generally favourable safety profile in early studies.
What has not been established is that it reliably regrows cartilage or changes the underlying course of osteoarthritis.
Whether any biologic treatment is appropriate depends on which structure is affected and how far the condition has progressed. Early cartilage change and end-stage bone-on-bone arthritis are very different clinical situations and should not be treated as equivalent.
Frequently Asked Questions
Does stem cell therapy regrow knee cartilage?
Current evidence does not establish that it does. Imaging findings in clinical trials have been suggestive rather than conclusive, and structural changes have not consistently matched how patients feel or function.
Is stem cell therapy for knees FDA approved?
No cell therapy is approved in the United States as a disease-modifying treatment for knee osteoarthritis. Approval status varies by country, and some products are approved only in specific jurisdictions for specific indications.
Is a higher dose better?
Not necessarily. In at least one dose-escalation study, low and middle doses performed better than the highest dose, which was associated with local swelling and inflammation.
Bone marrow or umbilical cord — which is better?
No head-to-head evidence establishes one source as superior for knee osteoarthritis. They differ in availability, preparation, cell characteristics and regulatory status rather than in proven effectiveness.
How long do the effects last?
Follow-up in published trials is generally short. Durability beyond one to two years remains one of the important unanswered questions in this field.
References
- First-in-human and multicenter phase I study of OSCA therapy for knee osteoarthritis. Experimental & Molecular Medicine. 2026.
- Phase I dose-escalation clinical trial to assess the safety and efficacy of umbilical cord-derived mesenchymal stromal cells in knee osteoarthritis. Stem Cells Translational Medicine. 2024;13(3):193.
- Three intra-articular injections of allogeneic umbilical cord-derived mesenchymal stromal cells in knee osteoarthritis: a phase-I clinical trial. Regenerative Medicine. 2026;21(1).
