Cell sources for orthopedic defects

The research directed toward gaining a better understanding of the role of stem cells in tissue injury has burgeoned in the past few decades. Accordingly, the development of methodologies to use stem cells has also increased. An improved understanding of the regenerative potential of adult (as opposed to embryonic) stem cells has resulted in a better acceptance of the study and use of stem cells by the general public. Importantly, patients with orthopedic injuries have benefitted directly from the remarkable advances in adult stem cell research. In addition to gaining a better comprehension of the mechanisms through which stem cells exert their effects, the discovery and isolation of stem cells from a large number of tissues has been an important advancement. This chapter will attempt to give the reader a better understanding of the sources of cells that are currently available for the clinician to apply and reliable sources for a basic scientist entering into the realm of stem cell biology to explore. The reader may notice there is an emphasis on mesenchymal stem cells (MSCs) derived from different tissues; the majority of information and therapies concerning orthopedic injuries is focused on MSCs. However, this is not to say that cells with characteristics and capabilities equivalent or even superior to MSCs that are viable therapeutic options for orthopedic defects do not exist. The available sources of stem cells, especially MSCs,1 and the discovery of several subtypes of stem cells within a given source, has grown dramatically. However, for the purposes of this chapter the discussion will be limited to sources that have been studied more thoroughly for bone repair. The use of bone marrow and adipose tissue as sources of stem cells, followed by other tissues (e.g., skeletal muscle) will be addressed, and specific topics covered include the isolation methods used to extract the stem cells, the delivery considerations, and the mechanisms of action.