Marc Darrow, MD.
Stem cell therapy for the knee generally involves injecting a preparation made from a patient’s own bone marrow or adipose tissue into the joint, or in some newer protocols, other biomaterials. These treatments are being studied mainly for symptom relief in knee osteoarthritis, especially pain and physical function.
Researchers believe any benefit may come from anti-inflammatory and cell-signaling effects. However, claims that these injections reliably regrow cartilage, reverse arthritis, or provide lasting structural repair remain unproven. The current evidence is promising, but it does not support describing stem cell therapy as a cure for knee osteoarthritis.
Overview
Knee osteoarthritis is a common cause of chronic pain, stiffness, swelling, and loss of mobility. Standard non-surgical treatments such as exercise therapy, weight management, anti-inflammatory medication, bracing, and injections may help many patients, but not everyone gets lasting relief. Because of that, interest has grown in regenerative treatments such as mesenchymal stem cell therapy.
The most commonly studied cell sources are bone marrow aspirate concentrate (BMAC) and adipose-derived stem cells (ADSCs). These therapies are usually discussed in terms of their ability to reduce inflammation, influence the joint environment, and possibly support tissue repair. What is better established in the current literature is improvement in symptoms such as pain and function. What remains uncertain is whether these therapies can consistently restore cartilage or alter the long-term progression of arthritis.
A January 2020 (1) study from Loughborough University in the United Kingdom suggests:
“Pre-clinical studies have demonstrated successful, safe and encouraging results for articular cartilage repair and regeneration (with intra-articular injections of bone marrow derived mesenchymal stem cells). This is concluded to be due to the multilineage differential potential (this ability to change into different cells allows for tissue repair), immunosuppressive and self-renewal capabilities of bone marrow derived mesenchymal stem cells, which have shown to augment pain and improve functional outcomes. . . Overall, the benefits of intra-articular injections of bone marrow derived mesenchymal stem cells were deemed to outweigh the adverse effects; thus, this treatment be considered as a future therapy strategy. To realise this, long-term large-scale randomised clinical trials are required to enable improved interpretations, to determine the validity of efficacy in future studies.”
Recent Studies on Stem Cell Therapy for Knee Pain
A May 2026 study (2) looked at whether injecting a patient’s own bone marrow concentrate into the bone near the knee joint could improve pain and function in people with knee osteoarthritis. The study followed 62 patients for 12 months. Patients showed meaningful improvement in pain and function scores throughout follow-up, and MRI scans showed improvement in bone marrow lesions at 3 months. Patients with lower body mass index appeared to do better, and younger patients tended to report faster pain relief. These findings are encouraging, but the study was retrospective and MRI follow-up was limited, so it does not prove lasting structural repair.
An August 2025 study (3) compared bone marrow aspirate concentrate with adipose-derived stem cells in 60 patients with symptomatic knee osteoarthritis. Patients under 50 received BMAC and those over 50 received ADSCs. Both groups showed significant improvement in pain, WOMAC scores, and range of motion over 6 months. Bone marrow samples generally yielded higher mesenchymal stem cell counts and slightly faster early recovery, but there was no substantial difference between the groups at the 6-month follow-up. This suggests that both treatments may help symptoms, but it does not establish a clear long-term advantage for one over the other.
In a March 2025 study (4) analyzed randomized controlled trials involving patients who received intra-articular mesenchymal stem cell injections without surgery. Compared with control groups, stem cell treatment was associated with significant improvement in WOMAC, VAS, and KOOS scores at both 6 and 12 months. This strengthens the case that stem cell therapy may provide real symptom benefit in knee osteoarthritis, although it still does not answer which preparation, dose, or patient group is best.
How Many Stem Cells? Does a Higher Dose Matter?
One of the practical questions in this field is whether a higher cell dose leads to better outcomes. So far, the answer appears to be no clear advantage.
A June 2024 study (5) evaluated three BMAC dose groups in 75 patients with early-stage knee osteoarthritis: 10 million cells, 50 million cells, or 100 million cells. All groups showed significant improvement in pain and function over one year, but there were no meaningful differences between the dose groups. Adverse effects were minimal and mainly limited to temporary pain and swelling after injection.
An August 2025 (6) dose-focused meta-analysis also found that lower doses may be sufficient. In that review, doses of 25 million cells or less were linked to significant clinical improvement, while higher doses did not show additional benefit. Taken together, these studies suggest that more cells are not necessarily better, and higher-dose therapy should not automatically be presented as more effective.
Is There a Difference Between Bone Marrow and Adipose-Derived Cells?
The current evidence does not clearly show that one source is definitively superior.
A study published in the Archives of orthopaedic and trauma surgery (7) evaluated 18 studies involving 1069 treated knees. Most studies used bone marrow-derived mesenchymal stem cells, while the rest used adipose-derived cells. The authors concluded that mesenchymal stem cell injections can represent a feasible treatment option for knee osteoarthritis, leading to improvement in pain and function regardless of cell source. They also found that patients with earlier-stage degeneration tended to do better.
In their 2016 study published in the journal Clinical and translational medicine,(8) researchers at Georgia Regents University noted that bone marrow-derived stem cells had been studied more extensively and might have stronger cartilage-forming potential in preclinical research than adipose-derived cells. But the same review also emphasized the need for more randomized clinical trials before firm conclusions could be drawn about efficacy and safety in real patients.
Multiple Injections Versus a Single Injection
Some clinicians have proposed that repeated injections may work better than a single treatment. In our 2018 study (9) we followed 15 patients with 20 treated knees through a short series of four bone marrow concentrate injections. Patients reported progressive improvement in resting pain, pain during activity, and functional scores across the treatment period, with the strongest results reported at final follow-up after the fourth injection. Our study was small, short-term, and uncontrolled.
Newest research
A 2026 systematic review and meta-analysis of randomized (10) evaluated mesenchymal stem cell therapy for osteoarthritis and found overall improvement in patient-reported pain and function outcomes. However, it also emphasized major variation among studies in cell source, donor type, dose, severity of arthritis, comparator treatment, and follow-up duration. That means the updated evidence strengthens the case for symptom relief but does not settle the bigger questions about ideal protocol or long-term structural benefit.
Also in 2026, a meta-analysis (11) focused specifically on autologous adipose-derived mesenchymal stromal cells found lower WOMAC scores at 3 and 6 months and lower pain VAS scores at 3, 6, and 12 months compared with controls, without a significant increase in adverse events.
Is Stem Cell Therapy for Knees Right for You?
The most accurate way to describe stem cell therapy for knee osteoarthritis is as an evolving regenerative treatment with encouraging short- to mid-term results for pain and function, but without definitive proof of durable cartilage regeneration or cure.The science is strong enough to justify interest and continued research, but not strong enough to support overstated claims that stem cell injections reverse arthritis, regrow cartilage in a predictable way, or eliminate the need for more conventional treatment in all patients.
Some patients may experience meaningful relief in pain and improved function after stem cell treatment, particularly in earlier stages of osteoarthritis. But the best available research still leaves important questions unanswered: which patients benefit most, which cell source is best, whether repeated injections are better than a single injection, what dose is optimal, how durable the benefits are, and whether structural improvement inside the joint truly lasts.
References
1 Doyle EC, Wragg NM, Wilson SL. Intraarticular injection of bone marrow-derived mesenchymal stem cells enhances regeneration in knee osteoarthritis. Knee Surgery, Sports Traumatology, Arthroscopy. 2020 Dec;28(12):3827-42.
2 Ezzi SH, Ding H, Wu S, Malik MA, Alshabi MM, Zhang W, Cao X, Huang J. Subchondral bone marrow aspirate concentrate injection improves clinical outcomes and reduces bone marrow lesions in knee osteoarthritis: 12-month retrospective analysis. Journal of Orthopaedic Surgery and Research. 2026 May 14.
3 Vitali M, Ometti M, Montalbano F, Spadafora S, Di Micco R, Salini V. Bone Marrow Aspirate Concentrate (BMAC) Versus Adipose-Derived Stem Cells (ADSCs) Intra-articular Injection Therapeutic Efficacy in Knee OA Correlated to Their Mesenchymal Stem Cell (MSC) Cellularity: An Exploratory Comparative Pilot Study. Indian Journal of Orthopaedics. 2025 Dec;59(12):2119-25.
4 Cao M, Ou Z, Sheng R, Wang Q, Chen X, Zhang C, Dai G, Wang H, Li J, Zhang X, Gao Y. Efficacy and safety of mesenchymal stem cells in knee osteoarthritis: a systematic review and meta-analysis of randomized controlled trials. Stem cell research & therapy. 2025 Mar 7;16(1):122.
5 Muthu S, Ramanathan K, Alagar Yadav S, Jha SK, Ranjan R. Increased cellular dosage of bone marrow aspiration concentrate does not translate to increased clinical effectiveness in knee osteoarthritis: a phase I dose escalation study. Indian Journal of Orthopaedics. 2024 Aug;58(8):1001-8.
6 Rahmadian R, Ariliusra Z, Kusuma KR, Ali H, Raymond B, Meksiko R. 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 Aug 30;20(1):812.
7 Migliorini F, Rath B, Colarossi G, Driessen A, Tingart M, Niewiera M, Eschweiler J. Improved outcomes after mesenchymal stem cells injections for knee osteoarthritis: results at 12-months follow-up: a systematic review of the literature. Archives of orthopaedic and trauma surgery. 2019 Aug 27:1-6.
8 Burke J, Hunter M, Kolhe R, Isales C, Hamrick M, Fulzele S. Therapeutic potential of mesenchymal stem cell based therapy for osteoarthritis. Clinical and Translational Medicine. 2016;5:27. doi:10.1186/s40169-016-0112-7.
9 Shaw B, Darrow M, Derian A. Short-Term Outcomes in Treatment of Knee Osteoarthritis With 4 Bone Marrow Concentrate Injections. Clin Med Insights Arthritis Musculoskelet Disord. 2018 Jun 18;11:1179544118781080.
10 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. Frontiers in Cell and Developmental Biology. 2026;13:1746471. doi:10.3389/fcell.2025.1746471.
11 Han JH, Jung M, Chung K, Moon HS, Jung SH, Baik SH, Koo J, Sim W, Kim SH. Autologous adipose‐derived mesenchymal stromal cell injection for knee osteoarthritis improves pain and function without a clear increase in adverse events: A systematic review and meta‐analysis of randomized controlled trials. Knee Surgery, Sports Traumatology, Arthroscopy. 2026.
References
8 Emadedin M, Labibzadeh N, Liastani MG, Karimi A, Jaroughi N, Bolurieh T, Hosseini SE, Baharvand H, Aghdami N. Intra-articular implantation of autologous bone marrow-derived mesenchymal stromal cells to treat knee osteoarthritis: a randomized, triple-blind, placebo-controlled phase 1/2 clinical trial. Cytotherapy. 2018 Oct 11. pii: S1465-3249(18)30605-4. doi: 10.1016/j.jcyt.2018.08.005. PubMed PMID: 30318332.
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