Anterior longitudinal ligament in diffuse idiopathic skeletal hyperostosis: Ossified or displaced?

Abstract

Diffuse idiopathic skeletal hyperostosis (DISH) is often theorized to be an ossification of the anterior longitudinal ligament (ALL). Using computed tomography (CT) imaging and cryomacrotome sectioning, we investigated the spatial relationship between the ALL and newly formed bone in DISH to test this hypothesis. In the current study, four human cadaveric spines diagnosed with DISH using CT imaging were frozen and sectioned using a cryomacrotome. Photographs were obtained of the specimen at 125 µm intervals. Manual segmentations of the ALL on cryomacrotome photographs were projected onto the three‐dimensional reconstructed CT scans. The presence and location of newly formed bone were assessed in relationship to the location of the ALL. The ALL could be identified and segmented on the photographs at all levels. The ALL was located at the midline at levels where no new bone had formed. At the locations where new bone had abundantly formed, the ALL was displaced towards to the contralateral side and not replaced by bony tissue. The displacement of the—morphologically normal appearing—ALL away from the newly formed bone implies that newly formed bone in DISH may not originate from the ALL. © 2018 The Authors. Journal of Orthopaedic Research® Published by Wiley Periodicals, Inc. on behalf of Orthopaedic Research Society J Orthop Res 36:2491–2496, 2018.

Dystrophic calcification and heterotopic ossification in fibrocartilaginous tissues of the spine in diffuse idiopathic skeletal hyperostosis (DISH)

“…Some studies have reported mineralization of the anterior longitudinal ligament in DISH, 21,24,40 whereas others report that the anterior longitudinal ligament does not undergo mineralization 1,21 or that it is displaced by the formation of ectopic mineral structures. 26 In the current study, when present in the histological sections examined, the structure of the anterior longitudinal ligament was typically preserved. However, in a subset of specimens, we detected focal regions of dystrophic calcification within the ligament, resembling those detected within the annulus fibrosus.…”

“…21,25 In contrast, recent studies in cadaveric tissues demonstrated that the anterior longitudinal ligament was morphologically normal in appearance and was displaced by ectopic mineral, but did not itself undergo aberrant mineralization. 26 Taken together, these findings underscore the need to identify and characterize the composition of the ectopic mineral formed in DISH, as well as the tissue types affected and associated cellular changes. The current study investigated these questions by combining radiological, histological, and physical analyses of human spine segments affected by DISH.…”