Quantitation of chondrocyte performance in growth-plate cartilage during longitudinal bone growth

[문형철]

태아, 출생 이후 아이들의 뼈는 compact bone이 아니라 연골이다. 

성장하면서 compact bone으로 변하고 growth plate로 남아 성장을 한다. 

이 관계를 잘 이해해야 진정한 성장치료를 잘할 수 있다.

Quantitation of chondrocyte performance in growth-plate car.pdf

ABSTRACT: The longitudinal growth of bone depends on the activities of individual chondrocytes of the growth plate. Each chondrocyte remains in a fixed location throughout its life, and there accomplishes all of its functions. Although a cell may perform several or all of its activities simultaneously, one of these will usually predominate during a particular phase of its life. The two most prominent stages are those of cellular proliferation and hypertrophy (including the mineralization of matrix) before the resorption of tissue during vascular invasion.

By applying recently developed stereological procedures and improved methods for the fixation of cartilage, we compared cellular shape modulation, various ultrastructural parameters (surface areas or volumes of endoplasmic reticulum, Golgi membranes, and mitochondria), the production of matrix, and cellular turnover for proliferating and hypertrophic chondrocytes within the proximal tibial growth plate of the rat. 

By the late hypertrophic stage, fourfold and tenfold increases in the mean cellular height and volume, respectively, and a threefold increase in the mean volume of the matrix per cell were achieved. The high metabolic activity of hypertrophic cells was reflected by a twofold to fivefold increase in the mean cellular surface area of rough endoplasmic reticulum, the Golgi membranes, and the mean cellular mitochondrial volume.

Rates of longitudinal growth were determined by fluorochrome labeling and incident-light fluorescence microscopy. Using these values and the stereological estimators describing cellular height, the rates of cellular turnover were calculated. The rapid progression of the vascular invasion front was found to eliminate, for each column of cells, one chondrocyte every three hours; that is, eight cells a day. The maintenance of a steady-state structure for growth-plate cartilage in rats in a steady state of growth thus necessitates efficient compensation for these losses, which is achieved by a high rate of

cellular proliferation and rapid hypertrophy. 

CLINICAL RELEVANCE: The development of quantitativehistology for bone and its application to the study of biopsy specimens from the human iliac crest have provided valuable new information about metabolic bone diseases which has aided in their diagnosis and treatment. This has become possible only by improvements in stereological methods and procedures for preparing undecalcified sections of bone for histological study. The essential knowledge and methods that are necessary for analogous studies of disorders of growth and of diseases affecting growth-plate cartilage are now available. Although biopsies of the iliac crest and proximal tibial growth plate are performed for diagnostic purposes, only qualitative analyses of sections of tissue have been possible so far. Improved methods of fixation of cartilage that permit the preservation of cellular size, shape, and ultrastructure with minimum distortion, and the development of stereological methods that are designed specifically for application to growth-plate cartilage, now permit quantitative analysis of this tissue and the application of such analysis to the study of disease states.