ABSTRACT

Orthopedic tissues are composed of heterogeneous populations of cells that regulate the development, repair, and adaptation of tissues in response to various environmental stimuli. Bone, muscle, cartilage, ligament, and tendon are increasingly viewed as plastic tissues that have the potential to remodel, perhaps due to interactions between various resident cells (Caplan 2007, Chargé and Rudnicki 2004). For example, it has been hypothesized that muscle satellite cells can mobilize in response to injured myo- bers, endothelial cells communicate with osteoblasts in bone development and synovial lining cells can aect chondrocyte phenotype and pathology (Philippou et al. 2007, Clarkin et al. 2008, Grellier et al. 2009, Rouwkema et al. 2008, Bakker et al. 2001). Currently, in vivo mechanisms for these phenomena remain unclear, but advances in in vitro systems may elucidate important cellular interactions.