The Pathophysiology Of Lumbar Disc Disruption

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Understanding the pathophysiology of discogenic pain is critical for understanding the treatment options. Discogenic pain represents a complex interaction of multiple pathologies. The intervertebral disc is an innervated structure capable of producing severe pain (7). In addition, pain fibers (nociceptors) are present in the outer posterolateral portion of the disc. Nociceptor afferent pain transmissions are relayed through the dorsal root ganglion (8). Ingrowth of granulation tissue and small unmyelinated fibers has been shown to occur in the degenerated disc (9). The degenerating disc loses water with a reduction in the nuclear hydrostatic pressure, leading to buckling of the annular lamellae and increased mobility. As the process continues, the annular wall shear stresses produce radial or concentric fissures of the annulus fibrosis, causing altered disc mechanics (10). The discogenic pain develops with any combination of annular fissures,

Lumbar Spinal Fusion

Fig. 1. Computed tomography three-dimensional reconstruction of lumbar spine following posterior spinal fusion. (Courtesy of Philips Medical Systems, Bothell, WA.)

Spinal Catheter

Fig. 2. Intradiscal electrothermal therapy catheter (Courtesy of Smith and Nephew, Menlo Park, CA.)

Fig. 1. Computed tomography three-dimensional reconstruction of lumbar spine following posterior spinal fusion. (Courtesy of Philips Medical Systems, Bothell, WA.)

delamination, or micro-fractures of collagen fibrils leading to mechanical distortion of the annular lamellae and sensitization of nociceptors with release of substance P. In fact, provocative discography triggers substance P release (11). As a result of stimulation of the dorsal root ganglion or direct chemical irritation of the nerve roots, the patient may experience referred pain to the buttocks and legs (39). Patients may present with one of three general types of disc pathologies. The first is the classic "leg pain" disc caused by disc herniation with nuclear migration through an annular tear and sciatica due to true dural tension. The internally disrupted disc with annular pathology, which produces back pain and variable amounts of buttock and leg pain but no true radiculopathy, causes the "back pain" disc. The "mixed" pattern of painful disc disease presents with features of both pathologies caused by small, contained disc herniations and central herniations.

There is a continuum of disc degeneration that starts with loss of nuclear hydrostatic pressure. This may lead to an annular tear. An annular tear can result in a contained disc rupture or a noncontained disc rupture. A contained rupture is contained by the posterior longitudinal ligament. Conversely, a noncontained rupture extends beyond the posterior longitudinal ligament. There are two types

Fig. 2. Intradiscal electrothermal therapy catheter (Courtesy of Smith and Nephew, Menlo Park, CA.)

of a contained rupture, a disc protrusion and a subannular-ligamentous disc extrusion. Likewise, there are two types of noncontained rupture, a transannular disc extrusion and a sequestered disc. Contained ruptures (contained by the posterior longitudinal ligament) may be treated with minimally invasive techniques whereas non-contained ruptures usually require surgical intervention.

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