Degenerative disc disease (DDD) is the primary cause of low back pain. The most important factor in the development of DDD is the vertical load force on the disc, increasing the hydrostatic pressure and facilitating discs degenerations. One of the most common conditions accompanying DDD is segmental instability of the spine. The pathogenesis evolves in three phases characterized by a progressive disc dehydration and loss of the disc height.

This phenomenon can be observed in magnetic resonance imaging (T2 weighted MRI) as a decrease of the water signal inside the intervertebral disc. It is considered as an indirect sign of the alteration of the composition (including glycosaminoglycans) and the structure of the intervertebral disk with, as consequence, a modification of the spine biomechanics. Animal studies showed that disc regeneration could be enhanced by a decrease of the hydrostatic pressure. This could be observed as a signal increase on T2 weighted MRI.

Recent quantitative MRI sequences now allow the quantification of glycosaminoglycans (GAG) concentration inside the cartilage and in the intervertebral disc.

The actual surgical trends are in favor of an anterior (intersomatic) vertebrak fusion, associated or not with a posterior fusion. These technics sacrifice the intervertebral disc and change the spine biomechanics.

Based on a pilot study, the investigators believe that the conservation and even a regeneration of the intervertebral disc is possible and allows the preservation of the spine biomechanics.

The purpose of the study is to analyze the relations between specific MRI signals, the GAGs concentration, and the functional outcome before and after the surgical treatment.

Inclusion Criteria:

• Patient with segmental instability of the lumbar spine
• Patient with planned surgery

Exclusion Criteria:

• clinical and iconographic signs of neurological compression
• intervertebral disc completely degenerated
• infection
• spondylolisthesis (superior to grade I)
• fracture
• neoplasia.