Morphometric and Morphological Study of Thoracic and Lumbar Intervertebral Discs in Guinea Pigs (<i>Cavia porcellus</i>)

This study investigates the gross morphological and morphometric characteristics of thoracic and lumbar intervertebral discs (IVDs) in guinea pigs, utilising micro-CT imaging and anatomical dissection. The findings reveal 13 thoracic and six lumbar IVDs were identified, with thoracic discs transitioning from rounded forms at T1-T3 to triangular and heart-shaped structures at T4-T13, while lumbar IVDs exhibited a consistently flattened heart shape. Morphometric analysis revealed statistically significant differences, with lumbar IVDs being larger in lateral and dorsoventral width, disc area, annulus fibrosus (AF) area and nucleus pulposus (NP) area, and ventral height compared to thoracic discs. Specifically, significant increases in lateral width and disc area were observed in lumbar segments L5 and L6, while thoracic IVDs demonstrated fluctuating alterations in some parameters, such as dorsal and ventral height. Histologically, both thoracic and lumbar IVDs feature a well-organised NP, AF and endplates (EP). The EP was composed of cartilaginous materials, including hyaline cartilage, fibrocartilage and calcified cartilage, and bony materials, including extensive secondary ossification centres with many large vascular channels and bone trabeculae. In conclusion, this study indicates that although thoracic and lumbar IVDs conserve key histological properties, their distinct morphological and morphometric characteristics in guinea pigs reflect their adaptations to biomechanical demands. However, due to some fundamental differences between human and guinea pig, use of this species as a model for human IVD research and interpreting the extracted data should be cautious.