Chondrocyte proliferation of the cranial base cartilage upon in vivo mechanical stresses.

Whereas the growth of the cranial base cartilage is thought to be regulated solely by genes, epiphyseal growth plates are known to respond to mechanical stresses. This disparity has led to our hypothesis that chondrocyte proliferation is accelerated by mechanical stimuli above natural growth. Two-Newton tensile forces with static and cyclic waveforms were delivered in vivo to the premaxillae of actively growing rabbits for 20 min/day over 12 consecutive days. The average number of BrdU-labeled chondrocytes in the proliferating zone treated with cyclic forces was significantly higher than both static forces of matching peak magnitude and sham controls representing natural chondral growth. Cyclic forces also evoked greater area of the proliferating zone than both static forces and sham controls. Thus, chondrocyte proliferation is enhanced by mechanical stresses in vivo, especially those with oscillatory waveform. Analysis of these data suggests that genetically coded chondral growth is up-regulated by mechanical signals.