ULTRASTRUCTURAL OBSERVATIONS ON THE OSSIFICATION OF THE SUPRASPINOUS LIGAMENT

Study Design. This study analyzed the process of ossification of spina l ligaments. Supraspinous ligaments excised during surgery were studie d by light and scanning electron microscopy. Objectives. The results w ere correlated to determine the mechanism of ossification of spinal li gaments. Summary of Background Data. Ossification of the ligamentum fl avum has been described in detail by Hiraoka, Yamaguchi, and others. H owever, the pathogenesis of ossification of the spinal ligaments remai ns unclear. Some studies have been performed by light and transmission electron microscopy, but no detailed investigation of the ossificatio n of the spinal-ligaments by scanning electron microscopy has been per formed. Methods. Specimens of supraspinous ligament were taken from 41 patients during spinal surgery. Ossification was diagnosed macroscopi cally and radiologically for 20 patients. The specimens were examined using light and scanning electron microscopy. Results. Collagen fibril s were 700-2000 Angstrom in diameter and were arranged in parallel. Th e ligament insertion divided into four zones and seemed to fit the des cription of Enthesis histologically. Close to the ossification region, there were a region in which some fibrils were thinner and branchings became slightly stronger, tending to form bridges of minute fibrils b etween other fibrils. Closer to the region of actual ossification ther e was a region in which extra-fibrillar substances completely deposite d. In the region of actual stances ossification, there were medullary spaces of varying sizes, and the surrounding collagen fibers were dens e and arranged in a lamellar fashion. Osteocyte lacunae had formed and the cells regarded to be the osteocytes were present on the inside. C onclusion. Ossification of the supraspinous ligament possibly occurs a s follows. Fibroblasts or chondrocyte drocyte-like cells respond to so me external stimulus, form an irregular network of fine fibrils, and p roduce acid mucopolysaccharide. These undergo calcification and capill ary invasion. Undifferentiated mesenchymal cells invade and are transf ormed into osteoblasts. Then osteogenesis ensues with progressive calc ification.