• Manos Stefanakis, Maan Al-Abbasi, Ian Harding, Phillip Pollintine, Patricia Dolan, John Tarlton, and Michael A Adams.
• Centre for Comparative and Clinical Anatomy, University of Bristol, Bristol, United Kingdom.
• Spine. 2012 Oct 15; 37 (22): 1883-91.

Study DesignMechanical and biochemical analyses of cadaveric and surgically removed discs.ObjectiveTo test the hypothesis that fissures in the annulus of degenerated human discs are mechanically and chemically conducive to the ingrowth of nerves and blood vessels.Summary Of Background DataDiscogenic back pain is closely associated with fissures in the annulus fibrosus, and with the ingrowth of nerves and blood vessels.MethodsThree complementary studies were performed. First, 15 cadaveric discs that contained a major annulus fissure were subjected to 1 kN compression, while a miniature pressure transducer was pulled through the disc to obtain distributions of matrix compressive stress perpendicular to the fissure axis. Second, Safranin O staining was used to evaluate focal loss of proteoglycans from within annulus fissures in 25 surgically removed disc samples. Third, in 21 cadaveric discs, proteoglycans (sulfated glycosaminoglycans [sGAGs]) and water concentration were measured biochemically in disrupted regions of annulus containing 1 or more fissures, and in adjacent intact regions.ResultsReductions in compressive stress within annulus fissures averaged 36% to 46%, and could have been greater at the fissure axis. Stress reductions were greater in degenerated discs, and were inversely related to nucleus pressure (R(2) = 47%; P = 0.005). Safranin O stain intensity indicated that proteoglycan concentration was typically reduced by 40% at a distance of 600 μm from the fissure axis, and the width of the proteoglycan-depleted zone increased with age (P < 0.006; R(2) = 0.29) and with general proteoglycan loss (P < 0.001; R(2) = 0.32). Disrupted regions of annulus contained 36% to 54% less proteoglycans than adjacent intact regions from the same discs, although water content was reduced only slightly.ConclusionAnnulus fissures provide a low-pressure microenvironment that allows focal proteoglycan loss, leaving a matrix that is conducive to nerve and blood vessel ingrowth.

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