TRANSPLANTATION OF ALLOGRAFT CHONDROCYTES EMBEDDED IN AGAROSE-GEL INTO CARTILAGE DEFECTS OF RABBITS

Objective: Durable healing of full-thickness articular cartilage defec ts has been considered for a long time as a highly desirable, but unli kely event to occur. In recent years, conflicting reports on the outco me of in vitro and in vivo studies on chondrocyte and cartilage grafti ng into animal and human joints have raised new arguments for and agai nst controlled repair of articular cartilage following injury. Some of the problems result from insufficient characterization of implant and repair tissue, and from too short follow up phases, Here we describe a new approach to repair articular cartilage defects in rabbit knees b y allografting chondrocytes cultured in agarose gels. Design: The impl ants were monitored over 6-18 months and graded histologically, immuno histochemically, and electron microscopically, using a grading scale b ased on seven evaluation criteria. Control implants of pure agarose pr oduced poor fibrous substitute tissue, insufficient healing and incomp lete filling of the cartilage defects. After transplantation of alloge nic chondrocytes embedded in agarose, the quality of the newly formed repair cartilage was superior with respect to type II collagen and pro teoglycan content and cellular architecture when compared with untreat ed defects. Superficial fibrillation and degradation were significantl y diminished or prevented. Results: New subchondral bone formed at the level of the previous subchondral bone, In most cases the repair tiss ue merged with the host articular cartilage, normal calcified cartilag e was the only tissue zone that did not participate in the integration of the transplant. By gross evaluation 24% of grafts showed an extent of recovery never observed in controls. The best results were obtaine d after 18 months when 47% of the grafts (N = 15) developed a morpholo gically stable hyaline cartilage. Conclusion: These studies demonstrat e that agarose-embedded chondrocyte may prove a valuable tool for cont rolled repair of articular cartilage defects.