Blount stapling of the proximal medial tibial growth was performed in 10-week-old domestic pigs. A total of 37 animals for up to 17 weeks were followed up. The histological evaluation showed a different reaction of the growth plate in the medial (stapled), central and lateral area. Up to 6 days after stapling the morphological features were characterized by deviations of the cell column from the axial alignment. Herniations of mature chondrocytes as well as isles of epiphyseal cartilage splintered into the adjacent metaphyseal cancellous bone were seen. From the 10th to the 11th postoperative day on there was a decline in the number of distal hypertrophic and degenerating cartilage cells due to impaired proliferation. Cell atrophy due to disturbed maturation or cell degeneration was evident. Local clusters of chondrocytes with loss of columnar arrangement indicated impaired chondrogenesis. Twenty-eight days after the operation coarser structures and changed alignment of cancellous bone characterized the morphological picture. The postoperative follow-up showed epiphyseal plates bounded by mature bone blocks or even a distinct sheet of horizontally oriented bone plates on the metaphyseal side. Many metaphyseal findings, such as augmented hypertrophic cells in the early postoperative period, or platelike limitations of the epiphyseal plate complete the morphological picture.
Medial stapling of the proximal tibial growth plate in ten-week-old pigs effects in the first instance a local reaction of the growth plate being first limited to the region between the staple branches. From the 4th-5th postoperative day on, there is a significant decrease of the growth rate, the surface area of cells in the zone of opening cells, and of the surface density of the adjacent metaphyseal spongiosa. From the 10th-11th day after stapling a significant decrease in the height of the metaphyseal columns and the growth plate occurs in the medial compartment as well as a trabecular broadening of the metaphyseal spongiosa in the stapled area. Subsequently, the surface density of the metaphyseal spongiosa is significantly lower, the volume density significantly higher than the control values. With advancing postoperative interval the stapling effects involve the whole growth plate. However, the central and the lateral compartments show always less distinct findings. Unilateral stapling of the growth plate brings about a significant diminution of the radiologically determined length of the epiphysis, metaphysis and the total tibia as well as an evident broadening of the growth plate.
Blount stapling of the growth plate induced changes in the metaphyseal architecture, which progressed in correlation to the postoperative follow-up. The stereological investigations revealed a subtile reaction of the medial stapled tibial plate in a total of 37 domestic pigs (10 weeks old) during the postoperative follow-up (up to 17 weeks). Zone 1, 380-1120 microns distal to the plate representing "bone modelling", and zone 2, 1180-2360 microns distally representing "bone remodelling", were investigated separately. The findings in zone 2 were very similar to zone 1 but were less extensive. The parameter most sensitive to stapling was the surface density; the trabecular distance showed parallel but less impressive findings. The specific surface and trabecular diameter changed with some delay. The last parameter to change was the volume density.
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