Morphologic Changes of the Intervertebral Disk During Growth

Abstract

Study design: Cross-sectional.

Objective: The aim of this study was to describe morphologic changes of the annulus fibrosus (AF) and nucleus pulposus (NP) in children during growth using magnetic resonance imaging.

Summary of background data: Little is known of intervertebral disk (IVD) maturation as opposed to degeneration, such as changes in relative AF/NP proportions and orientation during growth. Studies suggest that IVD plays a role in the etiology of pediatric spinal deformities. Therefore, understanding the morphologic development of the AF and NP during growth is key.

Materials and methods: An existing database of children aged 0 to 18 that had magnetic resonance imaging for indications unrelated to the spine were analyzed. The AF/NP were segmented semiautomatically from T1 to L5. The parameters: mean IVD height, cross-sectional area, slenderness (height/width ratio), volume (ratio), and relative position of the centroid of the NP within the IVD in three directions ( x , y , z ) were extracted, and compared between age, sex, and spinal level.

Results: IVD height increased modestly and predominantly in the low-thoracic and lumbar spine during the first 5 to 10 years of life. Cross-sectional area and thus volume increased steadily at all levels throughout growth. IVD slenderness decreased sharply in the first years of life and remains relatively stable throughout the remainder of growth. IVDs were smaller and more slender in females, especially in the mid-thoracic spine at early adolescence. In the upper-thoracic and mid-thoracic spine the NP comprises 10% to 12% of total IVD volume during growth, this percentage increases in the low-thoracic and lumbar spine towards 20% to 25%. In the anterior-posterior direction, the position of the nucleus increasingly shifts with age, possibly in line with the developing sagittal profile of the spine.

Conclusion: This study describes the development of thoracic and lumbar IVDs during growth and may be used as a reference for future studies on the role of IVD in the etiology of disk-related disorders.

Figure 1

T2-weighted magnetic resonance imaging scan. Example of a segmentation of T1–L5. Nucleus pulposus in orange and annulus fibrosus in blue.

Figure 2

Nucleus orientation analysis. A new coordinate system (x, y, z) was plotted in the center of both the intervertebral disk and nucleus pulposus. The relative center of the nucleus pulposus compared with the center of the total intervertebral disk was plotted and the distance between them calculated in three directions.

Figure 3

Scatterplot of mean intervertebral disk height (mm) (A), mean intervertebral disk cross-sectional area (mm²) (B), and intervertebral disk slenderness (C) of four intervertebral intervertebral disk level groups by age in males and females. Each dot represents the mean value at a intervertebral disk level in a single person. A Loess regression line is fitted for each intervertebral disk level. CSA indicates cross-sectional area.

Figure 4

Scatterplot of mean annulus fibrosus volume (mm³) (A), mean nucleus pulposus volume (B), and ratio of nucleus to intervertebral disk volume (%) (C) of four intervertebral intervertebral disk level groups by age in males and females. Each dot represents the mean value at a intervertebral disk level in a single person. A Loess regression line is fitted for each intervertebral disk level.

Figure 5

Relative change in center of mass of the nucleus pulposus within the intervertebral intervertebral disk throughout the spine, in three age groups, for males and females. Fitted with Loess regression lines, (A), change in the left-right orientation; (B), change in the anteroposterior orientation; (C), change in the craniocaudal orientation.