[Effect of marrow stromal cells derived chondrocytes on repair of full-thickness defects of rabbit articular cartilage].

OBJECTIVE: To investigate the feasibility of cartilaginous implants containing bone marrow stromal cells (MSCs) derived from chondrocytes in biological resurfacing procedures for repairing articular cartilage defect.

METHODS: MSCs derived from chondrocytes were obtained with high initial cell density subculture. An implant was constructed by dispersing the chondrocytes in a acid soluble type I collagen gel(5 x 10(6) cells/ml, final cell concentration). A full-thickness defect 3 mm x 5 mm was created in the trochlear groove of femur in 36 rabbits. A piece of cotton soaked in 0.5% trypsin was laid into the defect for 5 minutes, then the defect was filled with MSC/collagen gel implant on one side (n = 36), filled with a plain collagen gel on the other side (n = 18), and left empty as controls on the other side (n = 18). The animals were sacrificed at 4, 8, 12, 24, 32, and 48 weeks. The repaired tissue was examined and evaluated with Pineda grading scale.

RESULTS: In MSCs group, the implanted cells resembled well differentiated chondrocytes and were surrounded by metachromatic matrix and the reparative tissue resembled hyaline cartilage after 4 weeks; bone was formed at the base of the defects, the thickness of new cartilage was larger than tht of normal one after 8 weeks; the thickness was reduced proximally, approximating to that of normal cartilage, and chondrocyte columns was formed and subchondral bone and tidemark reappeared after 12 weeks; the thickness of the new tissue was about 55% of the normal tissue, with smooth surface and there were hypertrophic chondrocytes near the tidemark after 24 weeks; no hypertrophic chondrocytes were observed, indicating cessation of endochondral ossification after 32 weeks; the tissue architecture was the same as that at 32 weeks, hyaline-like cartilage persisting, with subchondral bone and tidemark in continuity after 48 weeks. The four layer cell orientation was not as clear as that of normal cartilage. The defects were partially filled with fibrous tissue in controls. At 32 weeks, erosive cartilage, naked subchondral bone and proliferative synovial membrane indicated the presence of osteoarthrosis. There were no statistical difference according to Pineda tissue scales in the specimens from the MSCs group between 24, 32, and 48 weeks, but there was significant difference between 4 weeks and 24, 32 and 48 weeks (P < 0.05). The joint function recovered after 2 weeks in MSCs group, while it deteriorated progressively in controls.

CONCLUSION: MSCs derived from chondrocytes improve repair of large full-thickness defect in articular cartilage. The reparative hyaline-like cartilage is stable differentiation after 24 weeks, maintains good joint function after 48 weeks.