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adjacent segment and found segmental instability above the fusion in 45% of their patients. Spinal stenosis increased above more than below the levels of the fusions. In a paper by Whitecloud and others in 1994 they found pseudoarthrosis higher with a greater number of fusion levels; however, this was discovered by analysis that the fusion had stopped early adjacent to a motion segment. They documented that if there are additional levels of degeneration, these should be incorporated into the fusion so that there would not be further degeneration.
In a paper by Chang and McAfee in 1989 they discussed fusion for degenerative spondylolisthesis and degenerative scoliosis. They stated that those are the results of chronic degeneration within one or multiple functional spine units and can result in abnormal motion, hypertrophic changes, vertebral collapse, translation, rotation. The manifestations can be back pain, radiculopathy or neurogenic claudication. The generally accepted operative treatment consists of neural decompression, arthrodesis, or a combination of both. They state frequently decompressive procedures render the degenerative spondylolisthesis and degenerative scoliosis more unstable resulting in progression of the olisthesis or scoliosis and recurrence of symptoms. They state that successful treatment of severe degenerative spondylolisthesis and degenerative scoliosis would encompass a thorough decompression and correction of the pre-existing deformities and immediate rigid fixation with spinal instrumentation and bilateral posterolateral fusion. In their study 21% of their patients had more than three-level fusions. They stated that wide laminectomies alone are often not sufficient in relieving neural compression. Pedicle and facet migration arid rotation may so severely compromise and kink the nerve roots that the only way to relax the involved neural tissue is to correct the pre-existing deformity. If left untreated without arthrodesis, this may result in progressive deformity, pain and late neurological deterioration.
Other papers point to the fact that arthrodesis alters the bioniechanics of the spine and creates a compensatory increased motion and increased mechanical load of the free motion segments adjacent to the fusion. In time these free segments may become a new source of pain. In this same paper by Even-Sapir, et al., in 1994 the majority of their fusions were three or more levels. In a paper by Haid and Dickman, January 1993, they state that the L4-5 disc has been postulated to be most prone to degenerative instability.
One study advocates that elective L4-5 diskectomy be combined with a fusion. Thirty-nine percent of the patients without fusion obtained a satisfactory outcome with 85% success results in patients with fusion.
Several surgeons advocate a posterior lumbar interbody fusion in (Continued on page 67)
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