Introduction

IntroductionLumbar hernias occur mostly in the posterolateral region of IVDs and mechanical loading is an important risk factor. Studies show that dynamic and static overloading affect the nucleus and annulus of the IVD differently. We hypothesize there is also variance in the effect of overloading on the IVD’s anterior, lateral and posterior annulus, which could explain the predilection of herniations in the posterolateral region. We assessed the regional mechanical and cellular responses of lumbar caprine discs to dynamic and static overloading.Material and methodsIVDs (n = 125) were cultured in a bioreactor and subjected to simulated-physiological loading (SPL), high dynamic (HD), or high static (HS) overloading. The effect of loading was determined in five disc regions: nucleus, inner-annulus and anterior, lateral and posterior outer-annulus. IVD height loss and external pressure transfer during loading were measured, cell viability was mapped and quantified, and matrix integrity was assessed.ResultsDuring culture, overloaded IVDs lost a significant amount of height, yet the distribution of axial pressure remained unchanged. HD loading caused cell death and disruption of matrix in all IVD regions, whereas HS loading particularly affected cell viability and matrix integrity in the posterior region of the outer annulus.ConclusionAxial overloading is detrimental to the lumbar IVD. Static overloading affects the posterior annulus more strongly, while the nucleus is relatively spared. Hence, static overloading predisposes the disc for posterior herniation. These findings could have implications for working conditions, in particular of sedentary occupations, and the design of interventions aimed at prevention and treatment of early intervertebral disc degeneration.

Introduction Intervertebral disk (IVD) degeneration is one of the major causes of low back pain. In the onset of IVD degeneration, the nucleus pulposus of the disk loses proteoglycans, decreasing the discs' capability to retain water. This is considered to detrimentally affect its biomechanical properties, making the disk prone to further degradation. Quantitative magnetic resonance imaging (MRI) techniques, such as T2- and T1-rho mapping, provide valuable information on the matrix status (proteoglycan content and distribution) of healthy and degenerating IVDs. We have developed a model to culture and load large (lumbar) IVDs, in which we can simulate IVD degeneration by injection of chondroitinase ABC (cABC; an enzyme that cleaves proteoglycans). The purpose of the current study is to characterize the changes in biomechanical, histological, and quantitative MRI parameters of caprine lumbar IVDs subjected to intranuclear cABC-injection. Materials and Methods Lumbar IVDs (36 total) with cartilaginous endplates were dissected from the spines of mature goats under sterile conditions. IVDs were randomly assigned to receive either no injection or injection (29G needle) of P83 µL PBS, 0.25 U/mL cABC, or 0.5 U/mL cABC. All IVDs were cultured in a bioreactor for 21 days under simulated-physiological dynamic loading conditions. Before injection and directly after culture, IVDs were scanned with a high-field MRI scanner (9T). T1-, T2-, and T1-rho mapping sequences were used to quantify the relaxation time parameters. IVDs axial deformation behavior during loading was analyzed and IVD stiffness was calculated from the load and displacement data collected during culture in the bioreactor. Matrix integrity of IVDs was studied on transverse paraffin sections stained with Safranin-O to assess proteoglycan content and distribution and Masson's Trichrome to assess collagen composition and structure. Results All biomechanical properties of the IVDs injected with cABC showed significant changes over the culture period. During preloading of the IVDs, within the first 8 hours of culture, creep behavior differed significantly between groups. A cABC dose-dependent subsidence was observed. Over the total culture period, disk height was reduced in all groups. However, cABC-treated groups showed significantly more loss in height. These discs progressively lost height during the entire culture period and stiffness of IVDs increased gradually over time. When comparing the images and quantitative MRI data from day 0 and day 21, significant changes could be observed in T2 and T1-rho values in the nucleus region for both the 0.25U and 0.5U cABC group. In the annulus, the apparent diffusion coefficient (ADC) changed significantly in the anterior and lateral regions. On histological sections, we observed a clear loss in staining intensity in the nucleus on Safranin-O sections, especially in the 0.5U cABC injected IVDs, with blurring of the posterior demarcation zone between the nucleus and annulus. In Masson's Trichrome stained sections, a ...

No abstract