Aseem Sharma
As a clinical neuroradiologist exposed to many MR scans of the lumbar spine, I have always found it intriguing that despite a number of predispositions affecting any given patient’s propensity to develop disc degeneration, individual discs within that patient often demonstrate marked variation in the extent of degeneration. My subsequent research into the natural history of disc degeneration has been guided by this “disc specific” nature of this disease process.
My initial research experiments were aimed at trying to analyze the pattern of disc degeneration as seen through the lens of clinical MRI, but deconstructed at the level of individual components of the intervertebral disc – the annulus fibrosus, the nucleus pulposus, and the end plates.1-3 Results of these studies pointed towards significant disruptions in either the annulus fibrosus (more frequent and more often affect the caudal segments of the lumbar spine) or the end plates (less frequent and more often affect the cranial segments of the lumbar spine) in progressive nuclear degeneration.1 In addition to suggesting that annular pathology is often antecedent to the nuclear degeneration, these results indicated that the disc-specific nature of disc degeneration could possibly be related to mechanical stresses that might initiate this process via disruption of the annulus or the end plates.
Given the complexity of motion experienced by the spinal column even during normal, day-to-day activities, we considered it likely that different discs would be exposed to different levels of mechanical stresses. Once again, clinical experience came in handy to test this hypothesis. Young patients presenting with back pain related to stress reaction in posterior elements of the lumbar spine provided a population in which the discs attached to the stressed vertebrae could be safely assumed to be exposed to higher mechanical stresses, while other discs could provide control discs that could be assumed to have seen a lesser extent of mechanical stresses.
The initial cross-sectional study, the results of which were presented at the International Society for Study of the Lumbar Spine Annual Meeting in 2014, demonstrated a higher burden of degeneration in stressed discs.4 A subsequent study published in AJNR,5 while confirming the initial findings, also demonstrated evidence for progressive nuclear degeneration in stressed segments with relative stability of appearance of nonstressed discs.