What is the mechanism of action of knee stem cell injections?

From the Guidelines

Knee stem cell injections are not recommended for the treatment of knee osteoarthritis due to the lack of standardization in available preparations and techniques used, as well as the limited and inconsistent evidence of their efficacy. The mechanism of action of knee stem cell injections involves introducing mesenchymal stem cells (MSCs) into damaged knee joints to promote tissue repair and reduce inflammation 1. These specialized cells have the ability to differentiate into various cell types, including cartilage, bone, and tendon cells, and release anti-inflammatory cytokines and growth factors that modulate the local immune response and create a more favorable environment for healing. However, the evidence from recent studies, such as the 2020 American College of Rheumatology guideline, strongly recommends against the use of stem cell injections for knee osteoarthritis due to the lack of standardization and inconsistent evidence 1. Similarly, the 2022 AAOS clinical practice guideline summary also does not support the use of stem cell injections for knee osteoarthritis, citing the limited and inconsistent evidence 1.

Some key points to consider when evaluating the use of knee stem cell injections include:

• The lack of standardization in available preparations and techniques used
• The limited and inconsistent evidence of efficacy
• The potential risks and adverse effects associated with the use of stem cell injections
• The need for further research to fully understand the mechanism of action and potential benefits of knee stem cell injections

Overall, while knee stem cell injections may hold promise as a potential treatment for knee osteoarthritis, the current evidence does not support their use, and alternative treatments, such as weight loss, exercise, and oral nonsteroidal anti-inflammatory drugs, should be considered instead 1.

From the Research

Mechanism of Action of Knee Stem Cell Injections

The mechanism of action of knee stem cell injections involves the use of stem cells to replace or repair damaged cells in the knee joint, potentially leading to improved pain and function outcomes.

• Stem cells are specialized precursor cells that can replace aged or damaged cells and maintain healthy tissue function 2.
• Mesenchymal stem cells (MSCs) are multipotent and exert anti-inflammatory and immunomodulatory effects, and can differentiate into multiple cell types of the mesenchyme, such as chondrocytes, osteoblasts, and fibroblasts 3.
• The use of MSCs in orthopedics may transition the practice in the field from predominately surgical replacement and reconstruction to bioregeneration and prevention 3.

Efficacy of Knee Stem Cell Injections

The efficacy of knee stem cell injections has been studied in several clinical trials, with varying results.

• A systematic review of 25 randomized trials found that stem cell injections may slightly improve pain and function up to six months after treatment, but the certainty of the evidence was low due to indirectness, suspected publication bias, and imprecision 2.
• A meta-analysis of nine randomized controlled trials found that stem cell therapy improved Visual Analogue Scale (VAS) score and Subjective International Knee Documentation Committee (IKDC) score from baseline to 24 months, but no significant difference was observed between the stem cell therapy group and the control group in IKDC score changes from baseline to 6 and 12 months 4.
• A systematic review of 10 studies found that intra-articular injections of MSCs were effective and safe in relieving pain and improving motor function in individuals with knee osteoarthritis in the short term, with significant improvements noticed in the MSCs groups via different outcome measuring tools like KOOS, VAS, WOMAC, and MRI 5.

Safety of Knee Stem Cell Injections

The safety of knee stem cell injections has also been studied, with generally favorable results.

• A systematic review of 25 randomized trials found that stem cell injections were associated with a low risk of serious adverse events, but the certainty of the evidence was very low due to indirectness, suspected publication bias, and imprecision 2.
• A meta-analysis of nine randomized controlled trials found that stem cell therapy had no obvious additional side effects compared to traditional treatments 4.
• A systematic review of 10 studies found that no significant adverse events were observed in the MSCs groups, and intra-articular injections of MSCs were safe in relieving pain and improving motor function in individuals with knee osteoarthritis in the short term 5.