The scientific work presents the results of radiological and histological studies of rabbit knee joint tissues in osteoarthritis and its correction with autologous platelet-rich plasma. The results of cytological studies of the synovial fluid of the affected joints and studies of the content of leukocyte subpopulations, C-reactive protein and erythrocyte sedimentation rate in the blood of the animals under study are also presented. The results of the studies showed that in the modeling of knee osteoarthritis using intra-articular administration of Yellow peel on day 7 in the blood of animals of the experimental group a sharp increase in markers of the inflammatory process was detected, namely: a significant increase in the absolute number of leukocytes (14.6±0. 2 g/l) and changes in the number of their subpopulations (increase in the number of: neutrophils 52.2±0.6, eosinophils 8.8±0.5, basophils 0.33±0.2, monocytes 15.2±0.5 and decrease in the number of lymphocytes 23.2±1.1), the content of C-reactive protein (CRP) 40. 75 μg/ml, which is 40 times higher, and an increase in the erythrocyte sedimentation rate (ESR) of 10.7 mm/h, which is 2.5 times higher than in the animals of the control group (4.8 mm/h), which was injected with an isotonic solution of sodium chloride. On day 7 after administration of Yellow peel, no radiological changes in the structures of the knee joint were detected. On the 14th day of the experiment, the content of leukocytes (14.2±0.2 g/l) and their subpopulations in the blood of experimental animals decreased (neutrophils 49.8±0.6, eosinophils 2.5±0.2, monocytes 7.1±0.3), except for the number of lymphocytes (42.1±1.5) and basophils (0.6±0.2). The content of C-reactive protein (23.5 μg/ml) decreased by 2 times compared to the values of day 7 (40.75 μg/ml). On days 21 and 28 of the experiment in animals of the experimental group, all studied parameters were lower compared to days 7 (14.6±0.2 g/l) and 14. At the same time, the number of leukocytes (12.6±0.2 and 10.8±0.1 g/l, respectively) and their subpopulations was within the reference values, but the erythrocyte sedimentation rate (7.8 and 7.3 mm/h, respectively) and the content of C-reactive protein (20.33 and 19.25 μg/ml, respectively) remained increased compared to the reference values and the animals of the control group. On day 21, a moderate decrease in the height of the joint gap in the medial part of the right knee joint (where the pathological process was formed) was noted during radiography. Microscopic examination of the knee joint cavity showed isolated fragments of articular cartilage, and the cartilage itself had significant areas of structural changes in the form of necrosis. On day 21 after osteoarthritis modelling, histological studies revealed the replacement of bone tissue located under articular cartilage with fibrous connective tissue, which also replaced red bone marrow in the bone cells. There was a significant impairment of articular cartilage endogenous osteogenesis, which was morphologically manifested by the absence of chondrocytes in its areas and the formation of isogenic groups of chondrocytes without the formation of columns of chondrocytes typical of endogenous osteogenesis. In the cells of spongy bone tissue, the growth of fibrous connective tissue located between the articular cartilage and the epiphyseal plate was recorded. On the 28th day of the experiment, a uniform decrease in the height of the joint gap was observed in the right knee joint during radiography. These changes indicate progressive degenerative changes in the knee joint of the experimental animals with cartilage loss. The histological changes in the knee joint tissues corresponded to the
changes observed on day 21. In view of this, an additional histological examination of the knee joint was performed on day 35, which revealed more significant destruction of articular cartilage. At the same time, cavities of various sizes and shapes were found in the cartilage tissue. With the correction of knee joint homeostasis (classical treatment regimen), the number of neutrophils (52.4±0.6) decreased by 31 %, eosinophils (8.8±0.5) by 12.5 %, the number of lymphocytes (21.2±1.2) increased by 31.3 %, and monocytes (13.3±0.5) decreased by 7% in animals of the first experimental group on day 7 after the start of treatment. The number of lymphocytes increased (21.2±1.2) by 7.3 % compared to the baseline (20.2±1.1). On day 14 after the start of treatment according to the classical regimen, the number of neutrophils (49.2±0.5) decreased by 61.5%, eosinophils (3.4±0.2) by 45 %, monocytes (4.2±0.6) by 37.9 %, and the number of lymphocytes (42.2±0.8) increased by 4.5 % compared to day 7 (21.2±1.2). The scientific material of experimental studies is of practical value in choosing a treatment strategy for animals with osteoarthritis.
