Sequence of development of innately regenerated growth-plate cartilage in the hindlimb of the neonatal rat.

Abstract

It has long been appreciated that the neonatal rat can regenerate the distal femoral growth-plate. Earlier descriptions of this process pointed to the age of the rodent and level and angle of amputation as significant modifiers of the regeneration process; but none identified the origin of the chondrocytes forming the growth-plate regenerate, nor described the time course and significant milestones of the process. Examination of these issues constitutes the objective of the present report. Fifty-four male, outbred albino rats sustained low femoral (48 rats) or midtibiofibular (six rats) hind-limb amputations when ten to eleven days old. They were killed after 0, 1, 2, 4, 7, 14, 22 or 29 postoperative days; and their amputation stumps were sectioned longitudinally. Twenty-four hr after amputation, the distal femoral periosteum was thickened and metachromatic regions were observed forming within it. Intraperiosteal cartilage was observed by the end of the second postoperative day in four of six limb stumps and, during the following week, expanded considerably in volume. Regenerated growth-plate cell architecture was recognized within the enlarging cartilage mass by the end of the second week; and, by the end of the fourth postoperative week, the regenerating growth-plate region had achieved considerable architectural maturity.