Changes of the chondrocytes ultrastructure and the volume of type II collagen in post-traumatic osteoarthritis

Objective To observe the changes of chondrocytes ultrastructure and the volume of type Ⅱ collagen in post-traumatic osteoarthritis through cartilage injury models of the femoral trochlea of rabbit. Methods The different cartilage injury models of the femoral trochlea of rabbit in vivo was made by impacting of different times. Rabbits were killed at each of the following intervals: 1 week, 4 weeks, 8 weeks after impacting injury. The ultrastructures of the chondrocytes were observed by transmission electron microscope (TEM). The changes of type Ⅱ collagen in cartilage tissue were detected by immunohistochemistry and in-situ hybridization. A two-way classification ANOVA for factorial design was used for statistical analysis. P values of <0.05 were considered statistically significant. Results One week, changes of chondrocyte in experimental group were limit. 4 weeks, Chondrocyte in experimental group was occurrent a series of changes: karyopycnosis, karyolysis、rough endoplasmic reticulum (RER) broaden, mitochondrion swelling, lysosome appear, cell membrane rupture, and so on. Immunohistochemical results showed that the matrix around chondrocytes and the trapped collagenⅡ gradually became lighter at 4 weeks, and the gray values of the 20 hits group and the 40 hits group were all higher than those of the control group, the difference was statistically significant (F=9.58, P<0.05, P<0.01). In situ tests showed the same results, the positive cells were distributed in the middle and lower part and deep layer of the shape shifting layer, with light staining at 4 weeks. The gray value of the 20 hits group and the 40 hits group was higher than that of the control group, and the difference was statistically significant (F=8.64, P<0.05, P<0.01). Immunohistochemical results showed that a large amount of fibrous tissue appeared in the matrix around chondrocytes, with low collagen typeⅡ content and generally no staining at 8 weeks. The staining gray value of collagen type Ⅱ expression in the 20 hits group and the 40 hits group was higher than that in the control group, and the difference was statistically significant (F=9.02, P<0.01, P<0.01). In situ tests showed the same results, chondrocyte necrosis was severe, and hardly any cells with positive staining were observed. The gray value of the 20 hits group and the 40 hits group was higher than that of the control group, and the difference was statistically significant (F=8.32, P<0.01, P<0.01). Conclusion Impact lead to cvartilage maxtrix injury and chondrocyte death, pathological changes of articular cartilage were severity with time lasting, pathological changes of articular cartilage were severity with impact times increase, Stop impact, pathological changes of articular cartilage were development. Key words: Osteoarthritis, post-traumatic; Chondrocytes; Knee injurys; Ultrastructure