On the Role of the Reserve Zone and Mechano-Regulatory Stimuli in the Development and Maturation of the Growth Plate: Observations and Models

Background. The subchondral epiphyseal bone plate between the epiphysis and the growth plate cartilage is formed by an unknown process. Objective. To examine if reserve zone chondrocytes could be involved in the development of the subchondral epiphyseal bone plate, by relating their intracellular stress-strain state to mechanobiological tissue differentiation theories. Methods. Multiscale elastic finite element models of the porcine proximal femoral physis at 20, 35, and 480 days after birth were created, based on histological observations. Findings. Simulating 15% compression of the growth plate produced intracellular maximum principal strains of 0.1–15% and compressive hydrostatic stresses of 0.15–0.4 MPa, depending on age and depth within the reserve zone. These values are within the range known to correspond with endochondral bone formation in fracture healing. Near the epiphyseal bone border the values for cellular compressive hydrostatic stress (> 0.15 MPa) and maximum tensile strain (0.1%) fall in the same range as found for hypertrophic chondrocytes at the metaphyseal bone growth front. Conclusion. The evidence suggests that growth plate cartilage has a secondary growth front at the reserve zone-epiphysis border that contributes to forming the subchondral epiphyseal bone plate.