Spondyloarthropathy in progressive ankylosis mice: ultrastructural features of the intervertebral disk.

Progressive ankylosis mice (ank/ank) spontaneously develop a joint disorder characterized by calcium hydroxyapatite deposition and bony ankylosis of the joints of the axial and the appendicular skeleton. Mice in this study were used to determine the extent of mineralization of the intervertebral disks and to determine their suitability as a model for ankylosing spondyloarthropathies. Intervertebral disks taken from affected mice from 4 to 18 weeks of age were studied by electron-microscopic, electron energy-dispersive X-ray microanalysis and selected-area electron diffraction techniques. Necrotic foci seen in light microscope studies were found to be massive accumulations of calcium hydroxyapatite crystals deposited within the extracellular matrix. Chondrocytes of older animals demonstrated what appeared to be postmortem changes and contained numerous large vacuoles.