Spinal Deformity Lumbar Fusion Instrumentation and Discography

Lumbar discography is being requested and utilized frequently in cases of spinal deformity14 and/or previous spinal fusion and instrumentation. We frequently perform discography upon patients who have undergone unsuccessful spinal fusion with or without instrumentation (too often without preoperative discography) to assess the presence or absence of discogenic pain at suspect levels and to study the internal integrity of adjacent segments.12,13 Spinal fusion with instrumentation is a major endeavor, and an increasing percentage of spine surgeons are required to know about disc integrity before operating on patients for whom fusion, with or without the use of instrumentation, is being considered.

A most unfortunate and potentially avoidable circumstance that we encounter is the patient who has had multiple spinal operations and fusion(s), with or without instrumentation, and still suffers pain and disability.1248 Too often MR imaging may be either impossible to obtain or severely degraded by the hardware in such patients. Furthermore, even if MR images are successfully obtained, disc integrity cannot be adequately assessed in many cases. We have demonstrated hundreds of concordant, intensely painful discs that were left in place when others had undertaken a purely dorsal fusion at the segment.1214 Experience and prior literature25,48 reveal that the odds of obtaining a desirable surgical outcome decline significantly with each successive surgical intervention. Discography, when performed upon the fused and instrumented spine, requires special skill and creativity. As in the unoperated back, it is important to study all suspect discs that are accessible and ideally one or two control levels.

We have investigated lumbar fusions performed with interbody metal cage grafts (Figure 6.3)49 and found that CT scans cannot reliably determine fusion integrity. Observation of what is commonly referred to as "viable bone" within such grafts does not reliably indicate the presence of solid fusion at that segment, as has been believed. We have often found such "bone" to be soft, permitting us to pass 22-26 gauge needles into and through it with ease. Furthermore, we have injected over 50 of these grafts within symptomatic patients to date, both fused and ununited at the segment(s) under study, and many of these were reported to be intensely and concordantly painful. When these painful cages have been surgically retrieved, the pain has been eliminated.

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Essentials of Human Physiology

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