Histomorphometric characteristics of the metaepiphyseal plate of the distal femur of lambs during the period of their intensive growth

Introduction Growth zone injuries are quite common and account for 15–30 % of all skeletal bone injuries in children. Complications occur in 2–14 % of patients. An adequate experimental animal model is needed to develop new methods for treating growth zone injuries. The purpose of the work is to identify patterns in the dynamics of histomorphometric characteristics of the metaepiphyseal cartilage of the distal femur of lambs during the period of their intensive growth. Materials and methods The metaepiphyseal cartilage of the distal femur of 12 lambs (aged 3.5 and 5.5 months, 5 males and 7 females) previously participating in an experiment on the effect of osteosynthesis pins on the structural reorganization of the metaepiphyseal cartilage was studied. Histological, immunohistochemical, and histomorphometric studies were performed. Results The zonal structure of the metaepiphyseal plate along with an increased proportion of PAS-positive structures in the outer layer of the border zone and in the calcified cartilage zone were determined. Masson staining revealed fuchsinophilic areas of the border zone matrix in the metaepiphyseal cartilage of animals aged 5.5 months, as well as an increase in the proportion of fuchsinophilic areas of the calcified cartilage zone compared to animals aged 3.5 months, which indicated increased mineralization. CD34 expression at 3.5 months was detected in the outer layer of the border zone, at 5.5 months the depth of vascular invasion increased, but did not reach the proliferating cartilage zone. A decrease in the thickness of the metaepiphyseal cartilage at the age of 5.5 months by an average of 18.2 % is due to a decrease in the thickness of the border zone by 1.9 times, while the thickness of the proliferating cartilage zone increased by 1.2 times. Discussion The changes observed in the main substance of the metaepiphyseal cartilage indicated that the processes of matrix calcification are more intense in lambs by the age of 5.5 months. The depth of vascular penetration from the diaphysis is more pronounced than from the epiphysis. Fractures in the growth zone during the period of intensive growth can be caused by the predominance of the border zone and by the proliferating cartilage zone. Conclusion Histomorphometric changes in the metaepiphyseal plate of the distal femur of lambs during the period of their intensive growth were characterized by a decrease in its thickness due to a marked decrease in the thickness of the reserve zone, while the thickness of the proliferating cartilage statistically significantly increased. The depth of vascular invasion in the border zone increased, but did not reach the proliferating cartilage zone, changes in the tinctorial characteristics of the ground substance indicated the activation of matrix calcification processes from the subchondral bone of the epiphysis and endomorphic ossification from the diaphysis.