Arthritis and ankylosis in twy mice with hereditary multiple osteochondral lesions: With special reference to calcium deposition

A murine autosomal recessive mutant named twy (tiptoe walking‐Yoshimura) mouse showing multiple osteochondral lesions including ankylosis of the vertebral column and limb joints underwent sequential histopathological analysis of posterior limb joint lesions and intervertebral disc lesions. In the articular cartilage, a decrease in alcian blue‐positive extracellular matrix and the presence of degenerated collagen fibers were found at the age of around 4‐8 weeks. Calcium deposits in the articular cartilage were found at that time and later in the articular space and synovial tissue. Calcium deposits were also found in the intervertebral discs at 4 weeks. Using electron microscopy, some of the crystals were seen inside small vesicles. In both joints, degeneration of, and calcium deposition in, the articular cartilage progressed with age, finally producing bony ankylosis. These histological observations suggest that calcification and degeneration of the articular cartilage are the major factors in the pathogenesis of joint disorders in the twy mouse, and this mutant mouse provides a good model for studying the process and mechanism of osteoarthritic lesions, destructive arthritis and ankylosis.