Histomorphometric analysis of an adolescent distal tibial physis prior to growth plate closure.

Purpose: Our current understanding of the rate and pattern of physeal closure is based on roentgenographic, magnetic resonance imaging, and qualitative histological studies. The purpose of this report is to provide a detailed histomorphometric/stereological analysis of a distal tibial human growth plate in the process of physiological epiphysiodesis.
Methods: A human distal tibial growth plate was sampled in three regions (anterior, central, and posterior), with each region further separated medially, in the middle, and laterally. The regions were assessed for the location and extent of bony bar formation as well as for physeal height. Companion sections from optimally fixed tissue in the distal 100 microm of the hypertrophic zone were analyzed for hypertrophic chondrocytic volumes.
Results: Physis closure started in the middle of the central region of the growth plate, with 46% of the volume in this area occupied by trans-physeal bridging bone. The growth plate was also narrowed with the lowest physeal heights evident in the middle of the central and anterior regions of the physis. Disruption of the regular columns of the physis was evident with the cells arranged in clusters with intervening areas of acellularity. The average hypertrophic cell volume was 5,900 microm(3) and did not significantly differ between different areas of the physis.
Conclusions: This is the first characterization of closure in a human distal tibial growth plate via optimum fixation and stereological techniques. The studied physis was during the earliest phases of closure and provides stereological support that the distal tibial physis closes in a central to medial direction.