The adult skeleton possesses 2 types of bone marrow: yellow and red. Yellow marrow has undergone adipose involution and is inactive. The red marrow possesses hematopoietic cells as well as 2 known populations of adult stem cells.1 Hematopoietic stem cells give rise to all cell components of circulating blood, such as erythrocytes, lymphocytes, neutrophils, and thrombocytes. The other stem cell population consists of mesenchymal stem cells (MSCs), which are also known as marrow stromal cells. MSCs have the potential to differentiate into connective tissue cells such as osteoblasts, osteocytes, adipocytes, and chondrocytes.