Morphologic and cytochemical changes in maturing and osteoarthritic articular cartilage in the temporomandibular joint of mice.

We studied the light microscopic, ultrastructural, and cytochemical characteristics of the temporomandibular joints of male ICR mice, from early neonatal life until they reached senescence, when spontaneous osteoarthritis is a common phenomenon. Aging of mandibular condylar cartilage was accompanied by decreasing total proteoglycan content and by an unmasking of collagen fibers, with no shift in collagen type. Fibronectin was also commonly present on the articular surface of specimens from old animals. Chondrocytes of aged mice contained an increased number of lysosomes, and their adjacent matrix vesicles reacted positively for acid phosphatase and arylsulfatase, but not for alkaline phosphatase. Such vesicles were also found to be devoid of calcium complexes and, thus, did not appear to be involved in the mineralization process. Similar age-related changes have been described in human mandibular condyles; hence, the male ICR mouse could serve as a useful model for studies of spontaneous osteoarthritis in the human mandibular joint.