Mechanical tension in distraction osteogenesis regulates chondrocytic differentiation

Differentiation of chondrocytes to cells of osteoblastic phenotype occurs during an interim period of bone development. fracture repair and distraction osteogenesis. To study the relationship between tension-stress and chondrogenesis. uniaxial strains (0 mustrains, 2000 mustrains. 20 000 mustrains. 200 000 mustrains, 300000, ustrains) were applied in a rabbit model of mandibular distraction osteogenesis. The results demonstrated that cell differentiation, apoptosis and tissue development in the newly formed gap tissue showed a correlation to the applied strain magnitudes. Only strains of 20 000 mustrains resulted in a statistically significant (P<0.05) formation of cartilage struts with embedded chrondocyte-like cells. However, chondrocyte-like cells were rarely detected in samples distracted at lower or higher strain magnitudes. Osteoblasts appeared to replace cartilaginous matrix by mineralized bone matrix. The phenotypic change from chondrocytes to osteoblasts was accompanied by a decreased proteoglycan synthesis, a change in the expression from type II collagen towards type I and involved asymmetric cell devisions and apoptotic cell death. Therefore, we suggest that mechanical strain is an external stimulus responsible for phenotypic cell alterations.