Fig. 2.

Histological appearance of a representative motion segment with horizontal presentation of ectopic mineralization associated with DISH. Images correspond to the specimen shown in Fig. 1b, T6-7. a Digital radiograph of the intact tissue prior to decalcification showing the localization of ectopic mineral within the motion segment (contoured by dotted yellow line). VB vertebral bone, IVD intervertebral disc. b Representative section stained with hematoxylin and eosin demonstrating the appearance of the intact section; scale bar represents 10 mm. The yellow box corresponds to an anterior region with features of heterotopic ossification imaged with a 10× objective (c–e), while the white box corresponds to a transition region from heterotopic ossification to the underlying fibrocartilage annulus fibrosus imaged with a 20× objective (f–h). c, f stained with hematoxylin and eosin; d, g stained with Masson’s trichrome; e, h the hematoxylin and eosin stained sections shown in c and f visualized with polarized light. Scale bars for c–h represent 100 µm. c–e Highlight features of heterotopic ossification along the anterior aspect of the motion segment, including compartmentalized bone marrow cavity (black asterisk) and organized lamellar bone (black arrowheads). f–h Characteristics of primary woven bone (black arrows) and organized nests of chondrocytes (white asterisk) associated with endochondral ossification. All images are oriented as shown in a