| Object To explore the effects of joint immobilization and PTH on the temporal sequences of spontaneous repair of articular cartilage. Methods Part1: A total of 36 Sprague-Dawley rats were anaesthetized. Then unilateral knee joints were opened using a medial parapatellar approach under sterile conditions and the patella was dislocated laterally to expose the articular surface of the femoral trochlea. Standardized cylindrical osteochondral full-thickness defects(2.5 mm in diameter; 2 mm in depth) were created in the weight-bearing area of the femoral trochlea with a 2.5-mm-diameter corneal trephine. 36 animals were randomly assigned into immobilization group and control group. The immobilization group was immobilized by a simplified miniature Ilizarov fixator. The distal femurs of the rats were harvested at the 2nd, 4th and 8th weeks. Then the gross observation and macroscopic examination was performed, to observe the repair tissue in the area of articular cartilage defects and the peripheral cartilage. It included the state of filling,the color,the luster, and so on. Part2: 24 male Japanese white rabbits, weighting 2.5~3kg, were anaesthetized by intramuscular injection of sodium pentobarbital. Then the both knee joints were opened using a medial parapatellar approach under sterile conditions and the patella was dislocated laterally to expose the articular surface of the femoral trochlea. Standardized cylindrical osteochondral full-thickness defects(4.5 mm in diameter; 4 mm in depth) were created in the weight-bearing area of the femoral trochlea with a 4.5-mm-diameter corneal trephine. Postoperatively, the 24 rabbits were randomly divided into two groups: The PTH group(n=12) was subcutaneously injected with 40?g/kg Synthetic human PTH five times a week. Control animals(n=12) were daily injected with vehicle. Four animals from each study group were sacrificed 4 h after the final drug administration at each time point(2W, 4W, 8W) and cartilage were collected for HE staining, mmunohistochemistry, qPCR and other tests. Result Part1: The repair rate of immobilization group and control group had no significant difference, and the regenerated tissue was mainly fibrous tissue. The control group showed neogenesis of hyaline cartilage-like tissue at the 8th week. The structure arrangement of peripheral cartilage was irregular in the immobilization group. At 2nd and 4th week, Wakitani score and Mankin score between two groups had no statistical difference. At 8th week, the Wakitani score and Mankin score of immobilization group was higher than the control group(P< 0.05). Two months after immobilization the rat articular cartilage Aggrecan and Col2 mRNA expression deceased, while the Col1a1 mRNA expression increased, and the difference was statistically significant(P<0.05). The articular cartilage MMP- 3 mRNA expression in immobilization group increased significantly compared with control group, the difference was statistically significant(P<0.05). Cartilage metabolic marker detection results showed that CTX-II level in urine the immobilization group was higher compared with control group after 8 weeks, the difference was statistically significant(P < 0.05). The expression of CTX- II of two groups had no statistical difference at the other time. Part2: The defects in PTH group were covered with more regenerate tissue, PTH injection can promote cartilage defect repair obviously.At the 2nd week, the Wakitani score of two groups was very high, but there was no statistical difference between the two groups. The Mankin score of two groups was low, but there was no statistical difference between the two groups.At the 4th week, the Wakitani score of PTH was lower compared with control group. The Mankin score of control group was significantly increased than PTH(P<0.01). At the 8th week, the Wakitani score and Mankin score of the control group was higher than the PTH group. The control group and PTH group had no difference in the cartilage repair tissue for the type II collagen immunohistochemical staining at the 2nd week. The cartilage repair tissue type II collagen of PTH group was trong positive stained, but the control group for type II collagen immunohistochemical staining was weak. PTH group compared with control group after 8 weeks' injection,the articular cartilage Aggrecan and Col2a1 mRNA expression increased, the difference was statistically significant(P<0.05), while Col1a1 mRNA expression change is not obvious, the difference was not statistically significant(P>0.05). MMP- 3 mRNA expression significantly decreased in the articular cartilage, the difference was statistically significant(P<0.05). PTH1 R mRNA expression also increased significantly, the difference was statistically significant(P<0.05). In the result of cartilage metabolic marker detection, we found that there was no difference between the PTH group and control group after 2 weeks, but there was statistically significant difference after 4 weeks and 8 weeks, the PIICP level increased significantly in the PTH group. Conclusion 1.Cartilage has certain ability of self-healing, knee joint cartilage defect in the first part of rats and the second part of the rabbit knee joint cartilage defect both could self- repair after 4 to 8 weeks. 2. Immobilization was no good for cartilage repair, and even lead to the degeneration of surrounding cartilage. The first part of the experiments proved the rat after immobilization could not be repaired well; the surrounding cartilage degenerated, especially immobilized for 4 weeks and 8 weeks. Wakitani score and Mankin score was higher than the control group. 3. PTH could stimulate the cartilage repair, protect cartilage. Wakitani and Mankin scores of PTH group were lower than the control group, and type II collagen staining was positive, suggesting PTH improved cartilage repair. |
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