‘Stress’ Distributions Inside Intervertebral Discs

Abstract

We investigated the distribution of compressive 'stress' within cadaver intervertebral discs, using a pressure transducer mounted in a 1.3 mm diameter needle. The needle was pulled along the midsagittal diameter of a lumbar disc with the face of the transducer either vertical or horizontal while the disc was subjected to a constant compressive force. The resulting 'stress profiles' were analysed in order to characterise the distribution of vertical and horizontal compressive stress within each disc. A total of 87 discs from subjects aged between 16 and 87 years was examined.Our results showed that age-related degenerative changes reduced the diameter of the central hydrostatic region of each disc (the 'functional nucleus') by approximately 50%, and the pressure within this region fell by 30%. The width of the functional annulus increased by 80% and the height of compressive 'stress peaks' within it by 160%. The effects of age and degeneration were greater at L4/L5 than at L2/L3, and the posterior annulus was affected more than the anterior. Age and degeneration were themselves closely related, but the stage of degeneration had the greater effect on stress distributions.We suggest that structural changes within the annulus and endplate lead to a transfer of load from the nucleus to the posterior annulus. High 'stress' concentrations within the annulus may cause pain, and lead to further disruption.

Diagnosis of discogenic low back pain in patients with probable symptoms but negative discography

“…Many reasons are related to the discogenic pain, such as disruption of the nucleus pulposus and anulus fibrosus, ingrowth of the granulation tissue and nerve endings into deeper layer of the annulus [13,14], irritation by inflammatory cytokines [15][16][17], mechanical stimulation associated with lumbar movement on the sinuvertebral nerve ending distributed in the outer one-third of the annulus and posterior longitudinal ligament [18], and epidural inflammation due to annular tears can also contribute to the pathogenesis of pain [19]. Although all mechanisms can exist in each patient, one or two of them maybe dominant in pain generation.…”

Relationship between annular tear and presence of Propionibacterium acnes in lumbar intervertebral disc

“…In normal disc, the posterior annulus is weaker than the anterior annulus [9], but sustains higher stresses [10]. Aging and degeneration would compromise disc structure and disturb stress distributions.…”

“…Aging and degeneration would compromise disc structure and disturb stress distributions. Adams et al [10] reported that in degenerative disc the compressive stress was reduced 30 % within the central nucleus region, but increased 160 % within the surrounding annulus. In addition, the changes of degeneration were greater on the posterior annulus than the anterior.…”

The influence of exogenous cross-linking and compressive creep loading on intradiscal pressure

“…Nucleus pressure was raised corresponding to increase in volume by the injection of fluid (Andersson and Schultz 1979;Ranu 1993) and fell when the volume was decreased by either surgical excision (Brinckmann and Grootenboer 1991) or nucleoplasty (Chen et al 2003). There was a reduction in the hydrostatic pressure in the functional nucleus of discs that were subjected to rigorous creep loading; 1-2 kN maintained for 2-3 h (Adams et al 1996). This reduction can be partially explained by an increase in facet loading, especially in lordotic postures.…”