Purpose of the study: There are limited data on the behaviour of intervetebral discs below arthrodesis for scoliosis. We have developed a reproducible MRI protocol for measuring the volume of the different components of the intervertebral disc and an original method for measuring disc hydration (ratio between the volume of the nucleus and the global volume). The discs studied were below fusions. The purpose of this study was to search for correlations between the disc volume and hydration and clinical outcome assess on standard x-rays.

Material and method: This was a prospective study conducted from 2005 to 2008. The series included 46 children with idiopathic scoliosis requiring arthrodesis (41 girls, 5 boys, mean age 15 years). The protocol included anteroposterior and lateral x-rays and MRI pre- and postoperatively and at 3 months and 1 year. 3D MRI reconstruction relied on a standard protocol validated in our research laboratory. These reconstructions produced a measurement of disc volume and its state of hydration. Two groups were identified using the plain x-rays: group A with what was considered to be a good result, well balanced spine and a horizontal disc subjacent to the arthrodesis; group B with what was considered a poor result with an unbalanced spine or oblique subjacent disc. Two groups were also defined as a function of postoperative reduction of the COBB angle. Group A’, reduction > 65% and group B’ reduction < 65%. Student’s t test was used for the statistical analysis.

Results: MRI series were obtained in 46 patients at 3 months and 28 at 1 year. At 3 months, there was an increase in nuclear volume (9.3%, p=0.056), global volume (5.2%, p=0.0017) and hydration (4.6%, p=0.056). At 1 year, the significant increases were, respectively, 15.4, 5.3 and 11.6%. At 3 months, there was a significant increase in disc volume in the groups A and A’. In group B, increase in disc volume (4.%, p=0.02) and hydration (13.9%, p=0.07) was only seen at 1 year.

Conclusion: This work enabled us to establish a significant correlation between increased disc volume and hydration as measured on the MRI and clinical outcome as assessed on the plain x-rays.