Time-relationship between bone growth and increment of bone mineral content in growing rats.

The aim of the study was to describe the time-relationship between the growth rate of the rat tibia and the increase rate of its mineral content. Appositional and endochondral bone growth rates were derived from sequential X-rays measurements of tibial widening and lengthening, respectively; the increase rate of bone mineral content was derived from sequential photon absorptiometry measurements of the proximal tibio-fibular site. The time-relationship of appositional growth rate and endochondral growth rate versus bone mineral content increase rate was mathematically described. The results allow a better understanding of the time-course of two distinct features of bone growth: increase in size and increase in mineral content.