6th Research HISTOLOGICAL AND ULTRASTRUCTURAL AGE RELATED CHANGES IN THE MENISCI OF THE KNEE JOINT IN RABBITS Fathy Ahmed Fetouh, Eman M.A. Abdelghany Department of Anatomy, Faculty of Medicine, Zagazig University ZUMJ Vol (14) No (3) July 2008: 2290-2306 Abstract Objective: The present work aimed to study the structural changes in the menisci of the knee joint with age progress in rabbits. Materials and methods: 3 groups of Egyptian rabbits at the age of one month, 6 months and 2 years were used (3-4 rabbits for each). The animals were killed by cervical dislocation and the menisci from one knee joint were fixed and processed histologically for light microscopy. The menisci from the contralateral knee were fixed and processed for transmission electron microscopy. Results: At the age of one month, the chondrocytes appeared less condensed and contained a considerable amount of secretory vacuoles and cytoplasmic organelles. The general matrix was observed to contain abundant collagen fibrils with marked variation in fibril diameter in addition to small amount of territorial matrix. At the age of 6 months, the chondrocytes displayed cytoplasmic basophilia and the cytoplasm was loaded with many secretory vacuoles of varing density and size. Some chondrocytes showed intracytoplasmic collagen fibrils. The matrix contained a condensed amount of collagen fibrils with no variation in fibril diameter. The territorial matrix was observed to contain a large amount of filaments, fibrils and protein-polysaccharide particles. At the age of 2 years, the chondrocytes displayed a considerable shrinkage and decrease in size in addition to extensive clear areas of the cytoplasm and disorganized cytoplasmic content. The matrix was found to contain the collagen fibrils with marked variation in fibril diameter in addition to localized aggregates of thick abnormal collagen fibrils. The territorial matrix was partially replaced by electron dense calcium deposits. Conclusion: The progress of age has severe impact on the structure of the menisci of the knee joint which makes them are vulnerable to injury in old than in young. Key words: Ultrastructure, Age changes, Menisci.