The normal and regenerated meniscus in rabbits. Morphologic and histologic studies.

The chronologic development of normal and regenerated menisci in immature and adult rabbits, studied by gross, histologic, and histochemical means, revealed that grossly regenerated menisci were less glossy and smaller than normal, with blunt margins and firm attachments to the synovial membrane. The normal meniscus of five-week-old rabbits consisted of fibroblasts and fibrocytes without cartilage cells. In 12-week-old rabbits fibrocytes in the normal meniscus had been transformed into round or oval cells lying within lacunae, the halos of which stained with safranin O. In the typical regenerated meniscus fibrocartilage cells appeared 12 weeks after meniscectomy in young rabbits and 24 weeks after meniscectomy in adult rabbits. Cartilaginous transformation occurred infrequently and only in isolated areas of the meniscus. Cartilaginous transformation in regenerated menisci appeared in 10.6% of the knees in young rabbits and in 8.1% in adult rabbits.