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information that helps establish what particular fusion procedure should be performed. The surgical outcome, expressed in terms of clinical benefit to the patient, has been shown to improve significantly when surgery follows a positive discogram versus a nonsymptomatic or a negative discogram.
The outer third of the disk is richly innervated and nerve fibers may extend as deeply as the middle third of the disk. Discography could produce low back pain and somatic referred pain, even in patients with no evidence of disc prolapse or nerve root compression. Discography determines whether a degenerative disc has become symptomatic. Many lumbar discs are painful upon disc stimulation and are intact externally. They exhibit a normal or near normal contour and no evidence of herniation or prolapse. In this condition, the affected disc is rendered painful by changes in its internal structure while its external appearance remains normal.
This is reported by Schwarzer, et al., in 1995 and Tehranzadeh in 1998. Freemont, et al., in 1997 demonstrated that isolated nerve fibers that express substance P within the diseased intervertebral discs are associated with pain suggesting an important role for nerve growth into the intervertebral disc in the pathogenesis of chronic low back pain. They stated that chronic low back pain is generally thought to be caused by nerve root compression. However, MRI often fails to show compression of neural structures, even in the presence of sciatica.
The North American Spine Society, September 1996, gave its approval on the use of discography. Ohnmeiss, et al., in 1997 concluded that disc disruption passing into the outer layers of the annulus, but not resulting in deformation of the outer annual wall, was as frequently associated with lower extremity pain as were discs with more superior disruption deforming the outer annular wall. They state that as early as 1958 investigators found that sciatica did not occur immediately with tension or traction of normal nerve roots, but only when roots that were inflamed were irritated. Lower extremity pain may originate from several spinal structures including ligaments, facet joints, musculature, disc, sacroiliac joints and compressed nerve roots.
Derby, et al., in 1999 concluded in their paper that patients with highly chemically sensitive discs appeared to achieve significantly better long-term outcomes with interbody combined fusions than with transverse fusions. Patients without disc surgery had the least favorable outcome. They stated that the intervertebral disc is now recognized as a common source of chronic axial pain.
It is now generally accepted that discogenic pain is not generated solely by mechanical stretching of the tissue causing nociceptive (Continued on page 65)
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