Orthopaedic Applications of Stem Cells

More than 33 million musculoskeletal injuries occur in the United States each year. Bone is capable of regeneration, and defects often heal spontaneously. However, cartilage, tendon, and ligament injuries usually result in replacement of the site by organized scar tissue, which is inferior to the native tissue. An increased understanding of cell biology and various tissue types may lead to the future possibility of using tissue engineering techniques to recapitulate the embryonic events that result in the development of native tissue. First, appropriate cells must be present to give rise to the structural tissue. Second, appropriate growth factors and differentiation stimuli must exist for the cells to proceed down the proper lineage. Third, a scaffolding matrix must act as a building block for cellular attachment, differentiation, and maturation into the desired tissue. Pluripotent mesenchymal stem cells (MSCs) with the ability to differentiate into multiple mesodermal lineages have been isolated from bone marrow, adipose tissue, and synovium. Stem cells have the advantage that they are unlimited in supply, easily harvested, and can be expanded in tissue culture to large numbers.