Stem Cell Therapy and the Future of Orthopaedics: An Expert Interview With Dr. Thomas Einhorn

Thomas A. Einhorn, MD


April 23, 2009

Editor's Note:

Stem cell research has caused much public controversy, sparking debate on ethics, cost, and legislation. Advocates of stem cell research believe that the use of adult stem cells holds promise of widespread applications, especially in the area of orthopaedics.

Pippa Wysong of Medscape sat with Thomas A. Einhorn, MD, to discuss his research on stem cell therapy as it may be applied to the repair and regeneration of bone and cartilage. Dr. Einhorn is Chairman of the Department of Orthopaedic Surgery and Professor of Orthopaedic Surgery, Biochemistry, and Biomedical Engineering at Boston University, Boston, Massachusetts.

Medscape: There has been a lot of talk in orthopaedics about the use of stem cells for treatment, such as bone regeneration. Why stem cells? What's special about them?

Dr. Einhorn: We're referring to the healing and regeneration of tissue in addition to the development of new tissue to help damaged parts of bone heal. In general, stem cells are nonspecialized cells that can divide and turn into other specialized cells, such as bone, brain, or blood cells. Stem cells are interesting because they have the potential to enhance healing in conditions in which our ability to do anything is limited, such as in avascular necrosis (AVN) and nonhealing nonunion fractures. Also, they have the potential to offer new types of treatments that are less invasive than some current approaches to these problems.

Medscape: Work with stem cells has been a politically hot topic in the United States. What is the climate like now for stem cell research?

Dr. Einhorn: Debate continues about the ethical issues relating to stem cell use in general, especially with respect to stem cells from fetal or embryonic sources. However, in orthopaedics, we're talking about the use of stem cells that are derived from a patient's own body -- adult stem cells. This is not from fetal or embryonic sources where much of the debate is centered.

Medscape: Can you explain more about adult stem cells?

Dr. Einhorn: A lot of people don't seem to understand that stem cells can be derived from adults. In fact, there are pockets of stem cells throughout the adult body: in the bone marrow, body fat, and other places. It's believed that they are present to help the body heal tissue that is wounded or damaged. Stem cells can be harvested from these various sources in the adult body. Embryonic stem cells have the potential to turn into, or differentiate into, a huge variety of tissues. Adult stem cells differ because they have a more limited potential to differentiate, and their properties vary depending on which part of the body they are harvested from. For the current orthopaedic areas being researched, adult stem cells appear to be sufficient. However, there are other important potential applications for stem cells that have a greater potential to differentiate.

Medscape: For orthopaedics, where would stem cells for clinical use come from?

Dr. Einhorn: They would be harvested from a patient's own bone marrow and then injected into the area where they are needed. This type of autologous transplant has the advantage of reducing the risk for rejection.

Medscape: What's special about stem cells from adult bone marrow?

Dr. Einhorn: Stem cells in human bone marrow are normally able to differentiate into cartilage, fat, or bone cells as well as fibroblasts. Of course, these are the types of tissue that would be the most useful in various orthopaedic applications. Two important types of stem cells being tried are mesenchymal stem cells, sometimes called marrow stromal cells, and hematopoietic cells.

Medscape: Where are things at in terms of research with stem cells in orthopaedics? Are there any clinical applications yet, or are things mostly in the lab?

Dr. Einhorn: Most of the research is still pretty basic, including animal studies. A small number of groups around the world are performing preliminary studies on human subjects for AVN and nonunion fractures. There are only a handful of researchers in orthopaedics in the United States doing this. One of the pioneers in this field is Dr. George F. Muschler at the Lerner Research Institute in Cleveland, Ohio.

Medscape: What is your own experience in terms of clinical applications?

Dr. Einhorn: We're in the middle of a small trial trying autologous stem cell therapy for AVN. We started with our first patient just over a year ago and expect to publish results soon.

Medscape: Can you describe to Medscape readers what you are trying?

Dr. Einhorn: This is still being studied, so there is no set protocol. However, yes, I can tell you what we are doing. First, we use a cannulated drill to create a cavity in part of the affected bone. We then harvest stem cells from the patient's own bone marrow. We take 120 cc of the marrow and spin it down so that we get 20 cc of concentrated stem cells. Immediately after the centrifuge, we inject the stem cells into the cavity. It's done all at once and is minimally invasive. The whole procedure takes about an hour.

Medscape: What do you hope the stem cells will do?

Dr. Einhorn: The idea is that once the stem cells are in the cavity, they will take nourishment from any remaining vasculature or blood supply and start to grow, differentiating into bone tissue. This new bone tissue should then use the surrounding necrosed tissue as a scaffold, putting living bone back where it belongs.

Medscape: What have you observed so far?

Dr. Einhorn: We've treated only 16 patients this way and can't make any general conclusions; it's more of a feasibility study. We have seen some new bone growth, but it's hard to say what the long-term results might be. Patients do report feeling significantly better immediately after the procedure, but that's likely from the decompression. It takes months for new bone to grow in.

Medscape: What about the potential of stem cell therapy for use in nonunion fractures?

Dr. Einhorn: The nonunion of fractures can occur for a number of reasons, and many won't heal without intervention. However, there are some nonunion fractures that even with intervention, still won't heal. There has been some success with growth factors. However, if stem cells prove effective in helping these fractures heal, then we'd have another option for these patients.

Medscape: How long do you think it might be before stem cell therapy will start appearing in clinical practice?

Dr. Einhorn: It could be in as little as 10 years if the various studies go well and prove that it's an effective treatment, but longer if there are glitches.

Medscape: If you could look into a crystal ball, where could stem cell therapies eventually lead orthopaedics? In what other areas does it have potential?

Dr. Einhorn: The ultimate goal would be the regeneration of cartilage, but that looks like it would be a little further off. Maybe one day patients with early signs of arthritis could have stem cells injected at the site where damage is starting and the cells would repair problems and prevent further degeneration. Another possibility is the repair or replacement of chunks of bone that have been lost due to trauma, such as gunshot wounds or other injuries. Wouldn't it be nice to place some sort of scaffolding material where some bone is missing; inject some stem cells; and, voila, after the cells grow, it's fixed? The potential is there, but there is a lot of work to do to get there.

Medscape: It sounds like a promising area. Thank you for talking to Medscape today.


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