Age Changes in Articular Cartilage of Rabbits

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Abstract
The cell density of articular cartilage from rabbits decreases with age, especially near the surface, where flattened cells seldom occur. The surface itself becomes irregular and small fissures appear. The cells in the middle zone are usually solitary. Their nuclei may be lobulated but this is an indication of ageing rather than amitotic division. In the cytoplasm, cytomembranes are rarely prominent; but bundles of filaments (each 90 to 100 A in diameter) are often seen. There is evidence that many cells have died: all stages from early degeneration to scattered remmants of organelles occur, often as whorled myelin bodies which represent phospholipid deposits. The lowered cell density with age is due rather to this cell death in situ than to wearing away of the surface cells. The matrix shows increased maturity of collagen fibers, which are no longer helically coiled and have a more ordered arrangement. Bundles of fine fibers surround the cells; coarse fibers diverge on each side of them. There are some very large fibers (up to 2,800 A in diameter) in close association with surfaces of cells showing evidence of senility.