Q: I have been hearing a lot about stem cell injections and was wondering if this would help my painful, arthritic knee?

There is a lot of exciting research and great interest in tissue engineering and regenerative medicine. However, there is also a lot of hype and misinformation out there. Tissue engineering is defined as the application of biological, chemical and engineering principles toward the repair, restoration, or regeneration of living tissues using biomaterials, cells, and factors, alone or in combination.1

The goal of tissue engineering is to regenerate damaged tissue. Tissue Engineering has three primary goals: Harvesting and isolating mesenchymal stem cells (MSCs), providing a scaffold onto which these cells are seeded so that their growth is organized and structured in an effort to duplicate a given tissue that is damaged, and assisting and promoting the growth of these MSCs with growth factors that cause the MSCs to ultimately become the tissue of interest.

There are two types of stem cells: embryonic stem cells, which are derived from fetuses and postnatal stem cells derived from adults. Embryonic stem cells have the ability to proliferate indefinitely in a test tube and the ability to produce all tissue types such as bone, cartilage or muscle. However, in the clinical setting they can cause an immune response in the recipient and can also cause tumors to grow. Furthermore, there are significant ethical concerns with harvesting embryonic stem cells as they are derived from human embryos. Currently in the U.S., the only research that can be performed on embryonic stem cells is that using stem cell lines that were in existence before 2009.

Adult stem cells have the advantage of not having these ethical concerns as they are harvested from the patient. Moreover, there is no immunogenic response as they come from you and also do not cause tumors to develop. However, they do not develop into various tissues as easily as embryonic stem cells do. Adult stem cells can be harvested from a variety of tissues: fat, blood, bone marrow, muscle and other tissue types. The number of stem cells seems to correlate with how much blood flow there is to a given tissue.

MSCs derived from fat or adipose tissue have been primarily used by proponents of regenerative medicine as adipose tissue is easily harvested and has a reasonable concentration of MSCs compared to other sources. Bone cells actually have more potential to differentiate into multiple cell types than fat cells, but harvesting cells from bone is more painful and invasive than harvesting fatty tissue, which most of us would be happy to donate. Anyone who has had a bone marrow biopsy can attest to the pain involved.

Patients who see me in the office with knee pain or knee arthritis often ask me if they would benefit from a stem cell injection. Currently, there is no good evidence in the orthopedic literature to recommend this. Insurance companies do not pay for this procedure, as again, there is no good evidence showing it to be efficacious. Thus, patients have to pay thousands of dollars out of pocket for this procedure. Given the lack of evidence to support it and the cost and possible risks, I do not recommend it. When injecting stem cells harvested from fatty tissue into an arthritic knee for example, these cells are not directed to grow cartilage nor are they directed to grow cartilage in the areas where your knee lacks it. Instead, these stem cells could equally differentiate into fat, bone, scar tissue or cartilage. In turn, you could grown bone on your own remaining cartilage, you could grow scar tissue on your ligaments, etc.

Tissue engineering is an evolving field with many possible exciting applications whose day will come, but unfortunately its clinical applications continue to be quite limited at the current time.

1 Laurencin CT, Ambrosio AM, Borden MD, Cooper JA Jr.: Tissue engineering: Orthopedic applications. Annu Rev Biomed Eng 1999; 1:19-46.

Dr. Rick Cunningham is a Knee and Shoulder Sports Medicine Specialist with Vail-Summit Orthopaedics. He is a Physician for the US Ski Team and Chief of Surgery at Vail Valley Medical Center. Do you have a sports medicine question youd like him to answer in this column? Visit his website at http://www.vailknee.com to submit your topic idea. For more information about Vail-Summit Orthopaedics, visit http://www.vsortho.com.

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Ask a Sports Medicine Doc: Fact and fiction of stem cells