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correlate with pain reproduction at lumbar discography. They state that there is inflammation in the subchondral bone adjacent to the end-plate resulting in reduced signal intensity on T1 weighed MRI sequences and increased signal intensity on T2 weighted MRI sequences equivalent to type I modic changes. Modic changes are in some cases the result of chemical inflammation from degenerative discs and may be a secondary sign on MRI of internal disc disruption and discogenic low back pain.
Toyone, at al., studied patients with low back pain and vertebral end-plate changes classified as either type A or type B, finding that type A changes correlated with a great degree of back pain and segmental hypermobility, while type B changes were more common in patients with stable degenerative disc disease. They suggest that modic changes may be a marker of segmental instability.
Braithwaite's conclusion is that their experience in patients with isolated type I end-plate changes and clinically severe pain responded well to diskectomy and fusion.
Wetzel and others in 1994 concluded that based on their study, discogenic pain syndromes can be treated with arthrodesis.
In a paper by Ransom, et al., in 1994, their indications for a pedicle screw fixation are lumbar spondylolisthesis with leg pain greater than low back pain, lumbar facet syndrome with low back pain, lumbar spondylolisthesis with low back pain, lumbar spondylosis with leg pain greater than low back pain, lumbar spondylosis with low back pain greater than leg pain. A fraction of each of their study populations had more than two-level fusions.
In a paper by Etebar and Cahill they discussed risk factors for adjacent segment failure following lumbar fixation. They stated that failure occurred when there was a floating segment, when such fusions were not anchored to the sacrum. With successful fusion there is a risk of adjacent segment degeneration and failure. Such failures most commonly take the form of facet overgrowth, ligamentous hypertrophy, and disc degeneration. Spinal canal compromise may also be associated with obvious spondylolisthesis, disc herniation, scoliosis or neck segment compression fracture. They discussed short, medium and long segments such as four or more vertebrae.
They stated that the adjacent segment failures were due to increased mechanical demand on the remaining mobile segments after the procedure. They stated that AOTA, et al., noted a 25% incidence of symptomatic adjacent segment stability after segmental lumbar fusions in which instrumentation was used. The incidence of spinal instability in women in this series was greater in patients older than (Continued on page 71)
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