A qualitative and quantitative analysis of the developing human lumbar vertebral column
The human adult lumbar vertebral column plays an important role in loadbearing and weight-transmission between the trunk and the lower limb, while its other functions include acting as a site for haematopoiesis, an area of attachment for soft tissue structures and protection of the spinal cord. While there is a rich source of research focusing on the internal trabecular architecture of the adult lumbar vertebrae, the ontogenetic development of this region is less well understood. This project aimed to both qualitatively and quantitatively assess the developing internal trabecular architecture of the lumbar vertebral centra and to document architectural changes throughout the maturation process. The project aimed to meet three specific objectives. Objective a). aimed assess regional variation in the trabecular architecture of the developing lumbar centra, for example how does the central region of the centrum differ from the peripheral region and are there any differences present between the superior and inferior, or anterior and posterior regions. Objective b). aimed to assess developmental changes in trabecular architecture within the lumbar centra, focusing on quantifying the differences in trabecular architecture between the fetal period, perinatal period, infancy and early childhood. Finally, objective c). aimed to assess vertebral level specific changes in trabecular architecture during development by identifying whether there are any differences in trabecular architecture between the lumbar levels L1, L3 and L5. The imaging modalities of radiography and micro-computed tomography were utilised to achieve these objectives. Qualitative and quantitative analysis of the developing fetal and perinatal lumbar vertebral centrum identified significant differences in trabecular architecture between central and peripheral regions of the developing centrum. In the fetal and perinatal periods both regions displayed a structure predominantly driven by ossification with trabeculae in close proximity to the primary centre of ossification thicker and more mature than in peripheral regions, which displayed a radial pattern of thin trabeculae extending outwards from the ossification centre. The presence of vasculature greatly influenced the internal architecture of the centrum from the fetal period into childhood, with a lower number of thicker, more plate-like trabeculae within the central region, forming a structure similar to that of the adult prior to the onset of load-bearing beyond in utero movements. This study has identified that the lumbar vertebral centra undergo three significant phases of development. The first phase is characterised by increased radiographic intensity and increased bone volume fraction driven by an increase in trabecular number. It is highly likely that this early period of bone mineral accrual acts as a preparatory mechanism to create a reservoir of minerals to facilitate re-organisation in the early postnatal period. The second phase is defined by significant loss of bone, in particular trabecular number and bone volume fraction, as well as increased remodelling of the trabecular struts into more rod-like structures. The final phase represents the period by which the internal trabecular architecture of the lumbar centrum is remodelled, likely in response to increased biomechanical demand. The attainment of developmental milestones, in particular sitting and standing unaided, which occur between around 6 months to 1.5 years of age, are considered of particular importance as these movements act to increase the compressive load placed upon the vertebral column leading to remodelling of the trabecular architecture into a mechanically optimal structure. From the perinatal period onwards, the fifth lumbar vertebral centrum consistently displayed a trabecular architecture linked to increased mechanical strength compared to the first and third lumbar levels. The likely reason for this is due to the increased load placed upon it as the most inferior lumbar vertebra. Furthermore, the positioning of the pelvis and the load transfer between L5 and S1 also likely contributes to this differing architecture. There was no evidence that the earlier appearance of the upper lumbar vertebral centra led to any differences in trabecular architecture, or that the developing lumbar lordosis prompted any changes in trabecular architecture between vertebral levels.
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