The transition zone above a lumbosacral fusion.

STUDY DESIGN: The clinical and radiographic effect of a lumbar or lumbosacral fusion was studied in 42 patients who had undergone a posterolateral fusion with an average follow-up of 22.6 years. OBJECTIVE: To examine the long-term effects of posterolateral lumbar or lumbosacral fusion on the cephalad two motion segments (transition zone). SUMMARY OF BACKGROUND DATA: It is commonly held that accelerated degeneration occurs in the motion segments adjacent to a fusion. Most studies are of short-term, anecdotal, uncontrolled reports that pay particular attention only to the first motion segment immediately cephalad to the fusion. METHODS: Forty-two patients who had previously undergone a posterolateral lumbar or lumbosacral fusion underwent radiographic and clinical evaluation. Rate of fusion, range of motion, osteophytes, degenerative spondylolisthesis, retrolisthesis, facet arthrosis, disc ossification, dynamic instability, and disc space height were all studied and statistically compared with an age- and gender-matched control group. The patient's self-reported clinical outcome was also recorded. RESULTS: Degenerative changes occurred at the second level above the fused levels with a frequency equal to those occurring in the first level. There was no statistical difference between the study group and the cohort group in the presence of radiographic changes within the transition zone. In those patients undergoing fusion for degenerative processes, 75% reported a good to excellent outcome, whereas 84% of those undergoing fusion for spondylolysis or spondylolisthesis reported a good to excellent outcome. CONCLUSION: Radiographic changes occur within the transition zone cephalad to a lumbar or lumbosacral fusion. However, these changes are also seen in control subjects who have had no surgery.

The pars defect as a pain source. A histologic study.

STUDY DESIGN: Tissue from the pars defects of six adult patients with symptomatic spondylolysis and spondylolisthesis was obtained at surgery. A histologic study was conducted to identify and characterize neural elements in this tissue. OBJECTIVES: To determine if nociceptive nerve endings were present within the pars defect of patients with symptomatic spondylolysis. SUMMARY OF BACKGROUND DATA: The origin of back pain in patients with spondylolysis remains uncertain. The defect in the pars interarticularis has been implicated as a possible pain source. METHODS: The soft tissue from the pars defect was obtained at surgery. A modified gold chloride stain was used to prepare the tissue for histologic examination. Tissue blocks were sectioned and studied under light microscopy. RESULTS: Neural elements were found in all specimens examined. Free nerve endings believed to have nociceptive function were identified in all specimens. The density of neural elements varied between specimens. CONCLUSIONS: The finding of neural elements, including free nerve endings within the pars defect tissue, suggests that the pars defect may be a source of back pain in some patients with symptomatic spondylolysis.

Effect of smoking and pulsed electromagnetic fields on intradiscal pH in rabbits.

The adverse effect of cigarette smoking on human spines has been noted indirectly. There is correlation of increased back pain among individuals who smoke heavily. The hypothesis of this study was that an environment of cigarette smoking is an adverse event and will create a reduced pH in the rabbit intervertebral disc. Electromagnetic fields, however, can defend against this adverse event and reduce the tendency toward acidic pH. Rabbits were exposed to cigarette smoke for 2, 4, or 6 weeks and their intradiscal pH measured. Cigarette-smoke-exposed discs demonstrated a consistently lower pH than did the discs of the machine control rabbits. The second group of rabbits were exposed to cigarette smoke and pulsed electromagnetic fields. The cigarette-smoke-exposed rabbits that were exposed to the pulsed electromagnetic fields for 4 hr/day demonstrated no change in their intradiscal pH, in contrast to those who were exposed to smoke alone. In conclusion, cigarette smoke exposure in rabbits consistently produces a lower intradiscal pH and pulsed electromagnetic fields can defend against this adverse effect.

Unilateral lumbar fusion.

Unilateral fusion of the lumbar spine is rarely necessary or indicated. However, in patients with a "far-out syndrome" requiring decompression or in cases where unilateral posterior element resection is necessary for any reason, it may be both necessary and indicated. This unilateral destabilization effectively removes one leg of the tripod, rendering that intervertebral joint potentially unstable. The charts and radiographs of 13 patients (seven men, six women) with an average age of 60 years (range, 25 to 76) who underwent unilateral fusion were retrospectively reviewed. Follow-up time ranged from 12 1/2 to 2 years with a median follow-up of 8 years. Eleven of the fusions were at one level, and two were at two levels. Seven patients had a far-out syndrome secondary to degenerative scoliosis; four were secondary to spondylolisthesis. Two patients had an osteoid osteoma involving a pedicle. A paraspinal approach was used in the majority of patients. Autologous bone graft was used in all patients. Unilateral pedicle screw fixation was used in the last patient in the series. The fusion rate was 85% (11/13). Three patients were smokers, two of whom developed pseudarthrosis. Disc space height did not appear to affect fusion rate. There was no progression of slip noted in any of the patients. One complication was noted in this group: a moderate postoperative infection, which cleared spontaneously.