Ossification of the Ligamentum Flavum in a Nineteenth-Century Skeletal Population Sample from Ireland: Using Bioarchaeology to Reveal a Neglected Spine Pathology.

Ossification of the ligamentum flavum of the spine (OLF) is rarely reported in individuals of European ancestry. It has, however, been observed in archaeological skeletons from Europe. The aim of this study was to revisit OLF rates, utilising a mid-nineteenth-century skeletal sample from Ireland. The hypothesis was that the OLF prevalence rate was similar to studies on non-Europeans. Spines from 345 individuals were analysed, and the extent of OLF recorded on the cranial and caudal attachment sites of each vertebra using the following classification system: Grade 0 (no change); Grade 1 (<2 mm); Grade 2 (2-4 mm); Grade 3 (≥4 mm). OLF was observed at prevalence rates of 83.6%. There was no disparity in prevalence based on sex, except for individuals aged 36-45 years at death in which the male rate was higher. Advancing age was a determining factor in the OLF occurrence with an onset in young adulthood (18-25 years), and most severe grades occurring over the age of 25 years. OLF coincides with spinal osteoarthritis, spondylosis deformans and Schmorl's nodes in both sexes, and with intervertebral osteochondrosis in females. The results of this study indicate that OLF is likely to be an understudied rather than rare condition in European populations.