Pathophysiology of the intervertebral disc and the challenges for MRI

Abstract

Through its ability to make relatively noninvasive and repeatable measurements, MRI has a great deal to offer, not only to clinical diagnosis of intervertebral disc disorders but also as a tool for basic research into disc physiology and the etiology of disc degeneration. In this brief review we outline the structure of the disc, the composition and organization of its macromolecules, and the changes that occur during disc degeneration, attempting to summarize features that have been or could become targets of MRI characterization. It is important to recognize, however, the fundamental limitation that most of the changes so far observed in MRI are consequences of alterations in cellular metabolism that occurred months to years previously and provide little insight into the current functional status of the tissue. There is therefore a need to develop MR techniques that directly characterize cellular activity and factors such as nutrient delivery on which it is critically dependent. We therefore briefly review cellular energy metabolism and nutrient transport into the avascular disc and consider the ability of MRI to reveal information about such processes. As a corollary of this discussion we also consider the constraints that the unusual transport properties of the disc impose on the delivery of contrast agents to the disc, since an understanding of these limitations is central to interpretation of the resulting images. MOST MRI INVESTIGATIONS of the spine are currently undertaken in an effort to establish the causes of back pain. However, the links between back pain and degeneration of the intervertebral disc are still, like most conditions involving congenital or acquired abnormalities of the disc, surprisingly poorly understood. This unsatisfactory situation reflects, in large part, our poor understanding of the physiology of the normal disc, and in particular, the relationships between function, or malfunction, and structure at the cellular and molecular levels. The requisite information is difficult to acquire due, largely, to experimental difficulties of various sorts. The intervertebral disc is closely coupled structurally, physiologically, and biomechanically, to the vertebral body and surrounding ligaments and musculature. The value of many measurements on excised discs in vitro is therefore severely compromised because these relationships are inevitably disrupted. In vivo approaches are also limited. Because these measurements generally involve extensive interventions, they have generally been confined to animals, but there is great variability in disc structure between species and few animals show degenerative changes resembling those in the human. Through its ability to make relatively noninvasive and repeatable measurements, MRI may here have a great deal to offer, not only to clinical diagnosis, but also as a tool for basic research (1).In this brief review we initially summarize the structure of the disc, the composition and organization of its macromolecules, and the changes that occur during dis...

Association of lumbar artery narrowing, degenerative changes in disc and endplate and apparent diffusion in disc on postcontrast enhancement of lumbar intervertebral disc

“…The blood circulation from aorta through lumbar arteries to the capillary network of the vertebral bone supplies nutrients that after transcapillary migration travel through the cartilaginous endplate into the nucleus where they slowly diffuse through the extracellular matrix to reach the cells in the centre of the disc. This nutrient supply route can potentially be disrupted at several points of which a few can be directly or indirectly evaluated with MR imaging [18]. MR angiography may depict atherosclerotic changes narrowing the lumbar arteries, which may diminish the blood supply to the capillary network in the vertebral bone.…”

Geometry of the vertebral bodies and the intervertebral discs in lumbar segments adjacent to spondylolysis and spondylolisthesis: pilot study

“…As a result, the wedging of the disc above the slipped vertebra is increased and the wedging of the disc below is decreased. This, in turn, will affect the biomechanical properties of the discs involved and their ability to withstand loads [24][25][26]. The morphology of the spine of individuals with isthmic spondylolisthesis compare to that of degenerative spondylolisthesis reveals some similarities and some distinct differences.…”

A Systematic Review of the Safety and Efficacy of Mesenchymal Stem Cells for Disc Degeneration: Insights and Future Directions for Regenerative Therapeutics

“…Disc degeneration is the progressive process of the loss of structural and functional integrity of the disc and is characterized by chemical changes in water and proteoglycan content [15,16,[18][19][20][21]. This sequential process is thought to be associated with a decreased cell number and a change in phenotype of disc cells, eventually leading to functional loss of the disc unit.…”

“…This sequential process is thought to be associated with a decreased cell number and a change in phenotype of disc cells, eventually leading to functional loss of the disc unit. As degeneration progresses, change in disc volume and shape is noted, together with overloading of adjacent structures (end plates, facet joints, and ligaments) [18,21]. Such degenerative changes may lead to altered spinal motion, potential disc herniation and compression of the nerve roots, and adjacent disc degeneration that may in time become symptomatic [22][23][24].…”