The Transition Zone Above a Lumbosacral Fusion

Abstract

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.