New Review: A Lot of Symptom Relief from Stem Cell Knee Injections May Be Due to Placebo-Type Effects

Key findings

• Of the studies included, contextual effects accounted for 60–66% of symptom improvement
• The specific, biological benefit of MSC injections for knee osteoarthritis was likely modest
• The ritual surrounding a stem cell injection may be more powerful than the effect of the cells themselves

I know a handful of people won’t like this article… but, it’s good to be objective. In my opinion, there are still a lot of efficacy questions in orthobiologics.

Given how high the out-of-pocket costs are for patients, how often are orthobiologics actually regenerating tissue? How often is it placebo, or other factors?

That’s what this systematic review set out to find. It should be noted that this is not a comprehensive review as it only includes a handful of studies. We need more well-controlled RCTs!

Further reading: Placebos for Knee Osteoarthritis: Reaffirmation of “Needle Is Better Than Pill”.

Contextual Effects May Dominate Symptom Relief from MSC Injections in Knee Osteoarthritis

Knee osteoarthritis (KOA) is one of the hottest regenerative medicine applications, with hundreds of potential stem cell-related therapies either in the pipeline or already deployed around the world. Over 250 million people are affected by the condition, and it’s a major challenge for the global healthcare system. Current treatments may or may not help with symptoms, while rarely addressing the true cause: loss of cartilage.

As you know, mesenchymal stem cells (MSCs) can be found in places like bone marrow, adipose tissue, umbilical cords, or iPSCs, and the early results have certainly been encouraging; however, the lack of RCTs has painted a less than clear picture.

In this new systematic review published in Frontiers in Medicine, researchers found that the majority of relief may come from contextual effects, rather than the cells themselves.

True Source of Benefit?

To better understand what drives symptom improvement with MSC therapy, researchers conducted a systematic review and meta-analysis of eight RCTs involving 467 adults with knee osteoarthritis. The trials compared intra-articular MSC injections to placebo and analyzed outcomes for pain and physical function at 6 and 12 months after treatment.

Each study reviewed delivered a single intra-articular MSC injection. Five of them used adipose-derived MSCs, two used bone-marrow-derived, and one used placenta-derived. The dosages ranged from 3.9 × 10⁶ to 100 × 10⁶ cells.

A unique aspect of this review was its focus on quantifying the role of contextual effects, factors like patient expectations, the therapeutic setting, and the experience of receiving an injection, in the observed benefits. Using a statistical approach called “proportion attributable to contextual effects” (PCE), the authors assessed how much of the overall improvement could be explained by these non-specific factors, as opposed to the biological action of the stem cells themselves.

The results? At 6 months, the findings suggest that approximately 61% of the improvement in function and 63% of the reduction in pain were attributable to contextual effects rather than the direct impact of MSCs.

At 12 months, the pattern was similar: contextual effects explained about 66% of gains in physical function and 50% of pain relief. These findings remained robust across different sensitivity analyses, although one trial had a notable impact on the pain outcome at 6 months.

Researchers stated, “Collectively, these converging findings suggest that the therapeutic ritual surrounding the intervention, rather than the cellular product alone, is responsible for the majority of the clinical benefit.”

Implications and Limitations

These results highlight what some researchers call the “efficacy paradox” of MSC therapy: while patients often report significant improvements after stem cell injections, most of the benefit may come from the context of the treatment—like a placebo—rather than the specific biological action of the cells.

This aligns with other studies in osteoarthritis, which have shown that the act of receiving an injection itself, whether MSC or placebo, can lead to substantial pain relief. The analysis also noted considerable variation between studies in terms of MSC source, dosage, and procedural details, but interestingly enough, contextual factors consistently accounted for more than half of the total improvement across all subgroups.

However, the overall certainty of evidence was rated as low, mainly due to small trial sizes, potential biases in study design and reporting, and limited long-term follow-up data. The review emphasized that while MSCs have a sound biological rationale and may have a specific effect, much of the observed benefit in current clinical practice is likely, at the very least, amplified by contextual factors. Understanding this balance can help clinicians set realistic treatment expectations with patients and guide future research to both optimize the specific action of MSCs and ethically harness contextual effects.

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Yin, F., Wu, H., Tong, D., Luo, G., Deng, Z., Yan, Q., & Zhang, Y. (2025). Contextual effects of mesenchymal stem cell injections for knee osteoarthritis: Systematic review and meta-analysis of randomized controlled trials. Frontiers in Medicine, 12, Article 1636181. https://doi.org/10.3389/fmed.2025.1636181