Age-related degenerative changes in the mouse mandibular joint.

The mandibular joints of ageing male ICR mice were studied by light and electron microscopy. A high incidence of degenerative joint disease was found relatively early in adult life, osteoarthrosis being evident by the seventh month. Initially the pathological changes were those of chondromalacia confined to isolated foci on the articular surface of the condylar cartilage. Later, characteristic signs of osteoarthrosis were noted, namely fibrillation, fibrous ankylosis, lipping and subchondral osteosclerosis. Ultrastructural examination indicated a marked heterogeneity in the articular lesions. Deep fissures and extensive cracks spread to the underlying matrix, and these were associated with severe alterations in its macromolecular structure. It is proposed that ageing chondrocytes produce a matrix which is increasingly incapable of withstanding normal mechanical forces, and this leads to the morphological changes recognized first as chondromalacia and then as osteoarthrosis.