A recent study found that fissures in the annulus fibrosis can create a biomechanical and chemical environment that is conducive to the ingrowth and formation of blood vessels and nerves, which may contribute to back pain in patients with disc degeneration—particularly of the lumbar segments. An examination and analysis of cadaveric discs used safranin staining to examine the proteoglycan loss and measure the water concentration in the 25 surgically-removed discs and compared the data from intact and disrupted annular region to quantify the extent to which a reduction in compressive stress might allow blood vessels to grow and thrive within annular fissures. Results indicated 54 percent less proteoglycan content in the fissured annulus than in the intact samples, with only a slight reduction in water content.
Examining the Link between Fissures and Nerve Growth
Persistent lower back pain—particularly of the lumbar intervertebral discs—often presents with severe symptoms that can lead to long-term disability and loss of earnings. Chronic pain may be the result of posterior annulus fibrosis and the stimulation of the sinuvertebral nerve. Previous studies have demonstrated that the injection of neurotoxins into the compromised discs can curtail this nerve pain for up to two years. While studies have shown that disc degeneration increases the risk of lower back pain, much of the focus of previous research has been on the association between structural defects, such as endplate defects and a loss of annular height, rather than biochemical changes.
Radial fissures in the annulus, with, or without disc herniation, are considered a strong indicator of LBP. The subsequent in-growth of blood vessels and nerves into these fissures can sensitize the disc area and cause inflammation, which may cause pain in some—but not all—with disc degeneration. Researchers involved in this study supposed a possible causal link between annulus fissures and nerve ingrowth.
Three Comparative Studies of Thoracolumbar Spine Segments
Three consecutive studies of surgically-removed cadaveric thoracolumbar spine segments from subjects who had experienced no spinal injury or extensive bed rest prior to death were compared with 25 samples taken from 18 cadavers of patients who had suffered from LBP, disc herniation, scoliosis, or spondylolisthesis prior to being deceased. The first study used die to identify annular fissures in 35 discs and radiographs to assess disc degeneration and height. Stress profiles were then performed on the segments in flexion and extension postures and then repeated following two hours of “creep” loading to simulate the rate of disc dehydration that might occur after a day’s activity. The discs were then dissected and photographed, then graded to determine the scale of degeneration.
The second study measured focal loss of proteoglycans from annular fissures in 25 samples using a custom-made software program, and a third study measured the loss of sulphated glycosamineoglycans in the fissured annulus.
Results—Higher Levels of Stress Reduction and Proteoglycan Loss in DD Samples
The analysis of the three studies indicated a compressive stress reduction of between 36 and 46 percent within the annulus fissures. The level was higher in degenerated discs. The fissured annulus regions had between 36 and 54 percent less proteoglycans than intact areas of the same discs, though the water content was only slightly reduced.
Pressure Reduction Contributes to Loss of Proteoglycans and Nerve Growth
The reduction of pressure inside the annulus fissures creates a biochemical environment that is conducive to the loss of focal proteoglycans. This allows for the in-growth of blood vessels and nerves within the fissured areas. These findings suggest that the injections of therapeutic neurotoxic dyes into the affected fissures could disable the in-grown nerves and help alleviate LBP in some patients.
KEYWORDS: Link Between Annular Fissures and In-growth of Blood Vessels and Nerves; fissures in the annulus fibrosis can create a biomechanical and chemical environment that is conducive to the ingrowth and formation of blood vessels and nerves; reduction in compressive stress might allow blood vessels to grow and thrive within annular fissures; possible causal link between annulus fissures and nerve ingrowth; reduction of pressure inside the annulus fissures creates a biochemical environment that is conducive to the loss of focal proteoglycans; posterior annulus fibrosis; persistent lower back pain