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Most patients are interested in stem cell treatments because of their potential for tissue regeneration and regrowth. While this is an exciting and rapidly developing part of orthopaedics, thus far many of the idealized outcomes have yet to be widely realized in clinical practice.

In order to better understand why, let’s first discuss what stem cells are. Stem cells represent a group of cells from your own body that have the possibility to become any type of cell in the future depending on the signals they receive. When you are conceived, you are composed of many stem cells that end up forming your organs and different tissues. This group of cells is powerful and plentiful at birth, which is why our healing potential is so strong at young ages. Throughout life, organs and tissues are constantly undergoing change, and dead cells are replaced by new cells derived from your own stem cells. As you grow up, the number of stem cells you have decreases, and stem cells start to lose their potential to regenerate, resulting in slower healing and signs of aging. In addition to having a regenerative potential, stem cells are powerful signaling cells. This means they can regulate the body’s inflammatory response, and they can organize which proteins are needed in each case to repair various injuries. Because of this ability, stem cells have been proposed as a potential regenerative source for patients with osteoarthritis, however, this has yet to be proven in humans.

For treatment purposes, stem cells can be extracted from blood, bone marrow, fat, muscle, and virtually every tissue in the body. Research efforts are currently focused on determining the ideal source for harvesting these cells.

Once the stem cells are obtained, there are two distinct methods by which they can be prepared and administered. One is a single harvesting or aspiration of the cells, which is then further concentrated via a centrifugation process similar to the one described for PRP and then injected into the target area. This is a same-day procedure in which the cells are extracted, concentrated, and then injected in the body. The most well-known procedure is a bone marrow concentrate. This procedure is FDA-approved and requires only minimal manipulation of the harvested cells with no chemical addition. The number and type of cells present within the aspiration, however, is generally not optimal; and has been found that bone marrow aspirates typically contain 0.001% of true stem cells. In addition, the cells may not have the best regenerative potential, and thus the final injection may yield a mix of stem cells with great, medium, and poor regenerative potential. However, when compared to other injections such as PRP, bone marrow aspirate has a greater potential to diminish inflammation because of the presence of interleukin-1 receptor antagonist, which is a quick and powerful blocker of inflammation within the joint.

The other stem cell process is a culture-expanded stem cell therapy or true stem cell therapy. This is a more involved process which requires a scientist to isolate true stem cells, test them for their regenerative capacity, culture the cells for a number of weeks so that they multiply, and then these selected cells are injected into the injured area. While true stem cell therapy may have more promise given a higher percentage of true stem cells isolated and injected, there is limited evidence and thus this is not FDA approved, and therefore cannot be performed in the United States if it is not within a clinical trial. All of these potential benefits have been proven mostly outside the body (in the laboratory), and the results and their safety profile have not been completely established in humans.

For both types of therapies, the mode of delivery of stem cells remains a challenge. As of now there are two main ways of implanting stem cells. The first mode is to deliver the stem cells via an injection with a fluid containing the cells. This is done when there is no specific injury, but rather a disseminated injury like osteoarthritis. The second is delivery of the cells through a scaffold, which is simply a membrane where the cells are implanted so they stay in the place of the injury, that can be implanted. The potential benefits of using a scaffold is that the cells can be placed exactly where they’re wanted.

One of the problems that has been identified with stem cells is that the implanted cells may not behave as intended. For instance, stem cells’ actions depend on signaling (they need a signal from the environment they are in to tell them where they are and how to behave), and when they are encapsulated in a scaffold, they might not be able to pick up those signals and therefore may not function in the way they’re expected to, creating bone instead of cartilage, for example.

Despite the rapidly increasing popularity and interest in stem cell use, the information available about stem cell injection outcomes in human patients is limited. The overall reported outcomes have been acceptable with a relatively safe profile. Furthermore, limited randomized clinical trials have looked at the effectiveness of bone marrow aspirate (BMAC) for the treatment of osteoarthritis. These studies have reported only modest improvements which could be more related to a placebo effect than the actual stem cells. In addition, researchers from the Mayo Clinic reported on twenty-five patients who had bilateral knee osteoarthritis. BMAC was injected in one knee, and saline (a harmless fluid and salt solution) in the other knee. They reported no difference in symptoms at six months or one-year post injection between the groups. Even less data is available on stem cell treatments using scaffolds.

Reported side effects for bone marrow aspirate procedure are similar to the ones described for PRP, with a reported frequency of adverse effects after the procedure ranging from 6% to 10% of patients. Self-limited pain and swelling are the most commonly reported adverse events. For culture-expanded stem cells, the most concerning adverse effect is that these cells can develop into unwanted tumoral cells. In addition, manipulation in the laboratory has risks of contamination of the cells.

Should I use stem cell injections to prevent getting osteoarthritis?

There is no evidence to support stem cells being used as a preventative treatment for knee arthritis. Current literature on the use of stem cells only provides evidence for diseased joints. Given the fact that no therapy is without risks, it is not recommended that these therapies be used for prevention of joint degenerative disease.

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