[Ultrastructural changes in articular cartilage affected by a non-physiological pH value of the synovial fluid]

The physiological pH-value of the synovial fluid (pH 7.2-7.4) is important for the integrity of normal articular cartilage. After the intraarticular injection of acid (pH 4.0) or alkaline (pH 10.0) isoosmolale buffer solutions into the knee joints of young rabbits ultrastructural changes are seen by the aid of transmission electron microscopy. The number of cell organelles in the chondrocytes (rough endoplasmic reticulum, Golgi-complex, mitochondria) is diminished and the number of intracytoplasmic filaments is increased. The intercellular matrix shows a looseness of the collagen fibre mesh work, swollen and split collagen fibres, the appearance of numerous coarse rounded structures with an electron dense envelop, and a loss of matrix granules. These results are interpreted as regressive changes, and they are discussed in the context of an activation of proteinases.