INTRODUCTION

Disc degeneration is known to gradually increase with age and spine overloading at young age may accelerate this process. Recently, we displayed different disc characteristics between young elite skiers with diverse training histories using quantitative magnetic resonance imaging (MRI)¹.

The present study is a 2-year follow-up of the discs and of the vertebrae in individuals reporting different training doses using quantitative MRI.

METHOD

35 students (Table 1) were recruited from schools with and without athlete competitive sports programs. The thoraco-lumbar spine of all individuals was examined at baseline and at the 2-year follow-up with the same 1.5T scanner and imaging protocol, including standardized sagittal T1- and T2-weighted sequences with FOV=480x480mm², thickness=4mm, TE/TR_T1=<90/560ms, TE/TR_T2=110/4463ms). After inclusion, the individuals were sub-grouped into high (>5 hours training/week, n=24 of which 22 were athletes) and low-to-normal training dose (0-5 hours training/week, n=11).

The discs (between S1 and T11, n=7) and vertebrae (L5-T11, n=7) were outlined on the mid three slices of the spine in the T2-weighted images. The mean signal intensity (SI) in the discs and vertebrae were normalized to the SI of CSF (hereafter referred to relative SI). Violin plots, displaying the probability density of data, were used to visualize differences between groups. Parametric (t-test and chi-square) and non-parametric (Mann-Whitney U test) tests using p<0.05 were used to evaluate statistical differences in demographics and MRI findings, respectively.

RESULTS

Disc findings

At baseline, there was a significant difference in relative disc SI between individuals reporting different training doses for whole spine, as well as for lumbar and thoracic spine separately (Figure 1). Individuals reporting >5 hours training/week (high training dose) had 11% lower median value at baseline compared to individuals reporting 0-5 hours training/week (low-to-normal training dose). Individuals reporting low-to-normal training dose displayed a significantly larger SI-decrease over time for whole spine than individuals reporting high training dose. There were no significant differences between groups at follow-up.

Vertebral findings

There was a significant difference in the relative vertebral SI between the groups at both baseline and follow-up for whole spine as well as for lumbar and thoracic level (Figure 2). Individuals reporting high training dose had 9% lower median value at baseline compared to individuals reporting low-to-normal training dose, and 14% lower at follow-up. The relative vertebral SI showed a decrease over time for both the lumbar and thoracic spine. When stratified for training dose, the decrease did not statistically differ between groups.

DISCUSSION

With quantitative MRI based on a conventional imaging protocol, we have revealed changes in disc and vertebra over time and showed differences in discs over time between individuals reporting high and low-to-normal training doses.

The differences between groups might be an effect of the load on the spine during a longer period, slightly accelerating tissue changes in the higher loading group normally seen with increasing age. This may represent very early signs of a disc degenerative process.