Histomorphometric analysis of the rat proximal tibial metaphysis by "linear scanning"

Twenty-four female Sprague-Dawley rats (10 weeks old, 200g BW) were either sham-operated (n = 6) or ovariectomized (ovx). Ovx rats were divided into 3 groups (n = 6 each): ovx; ovx + 1,25-(OH)2D3; ovx + 1,25(OH)2D3 + 1,24,25-(OH)3D3. The vitamin D metabolites were fed orally starting the day after surgery. After 7 weeks all rats were sacrificed and the proximal tibiae were processed undecalcified for quantitative histomorphometry. Conventional histomorphometric analysis of the distal zone (greater than 1 mm from the growth cartilage) of the tibial metaphysis revealed a dramatic loss of cancellous bone mass in ovx rats. Both 1,25(OH)2D3 and the combination of 1,25(OH)2D3 with 1,24,25(OH)3D3 prevented the bone loss in the distal zone in ovx animals. Measurements in the proximal zone (less than 1 mm from the growth cartilage) of the tibial metaphysis were performed with a newly developed technique that utilizes the advantages of automatic image analysis, and that we propose to name "linear scanning". This method revealed a significantly decreased hard tissue mass at about 100 microns and within 800 to 950 microns distance from the growth plate in ovx rats. However, ovx rats reached normal amounts of hard tissue within 250 to 450 microns from the growth plate. The results obtained by linear scanning suggest that the obvious loss of cancellous bone mass in the distal zone of the tibial metaphysis in growing ovx rats is not a consequence of structural changes in the proximal zone.