Instrumented versus Uninstrumented Fusion in Degenerative Spondylolisthesis

Research output: ThesisPh.D. thesis

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Due to inconsistencies in the literature, and no clear guidelines for lumbar fusion in the elderly, this PhD study aimed to investigated the outcome and cost effectiveness of added instrumentation in lumbar spinal fusion in the elderly, when treating degenerative spondylolisthesis. Further, we aimed to investigate the importance of a preoperative sagittal imbalance in one-level in-situ fusion, regardless of fusion method.

A randomized controlled trial was performed, 108 were included and by randomization divided into two groups. Group 1 underwent standard midline sparing decompression and uninstrumented fusion, with allograft mixed with local autograft
from the decompression, due to degenerative spondylolisthesis and spinal stenosis. Group 2 underwent the same standard midline sparing decompression, and in addition to the bone graft, pedicle screw instrumentation was performed at the index level.
At surgery, patients answered a standard battery of questionnaire, including Oswestry Disability Index, EuroQoL-5D-3L, VAS-back and -leg, Zurich Claudication Questionnaire and ShortForm-36. A lateral 36” X-ray was taken before surgery, to measures preoperative sagittal balance. 
Patients were followed for two years after surgery, with patient reported outcomes and 36” X-rays at one- and two-year follow-up. At one-year follow up, a CT-scan was performed to investigate fusion status.

Results We found no difference in disability, quality of life or pain at one- and two- year follow up. There was a marked difference in fusion rates in favor of the instrumented fusion (94% vs 31%) Seven patients underwent reoperation in the uninstrumented group versus one patient in the instrumented group, at two-year follow up. Alongside the randomized trial, a micro-adjusted economical evaluation was performed. The accumulated costs were based on a journal audit, and generation of costs were done from a bottom-up perspective. With a moderate increase in quality adjusted life years in the instrumented group of 0.095, and an increased cost of €146, we found an incremental cost effectiveness ratio of €1536, suggesting that instrumented fusion was cost-effective. When performing sensitivity analysis based on all reoperations or based on standard hospital reimbursement rates, instrumented fusion dominated uninstrumented fusion with better outcome and lower costs, suggesting a moderate cost saving with instrumentation. When investigating the effect of a preoperative sagittal imbalance, we found a correlation between preoperative sagittal vertical axis and preoperative patient reported outcomes, but there were no correlations to sagittal vertical axis and outcome at either one- or two-year follow up. 

Conclusion In conclusion, we found that, although there were no statistically significant differences between groups based on patient reported outcomes, patients in the instrumented group had fewer reoperations and a higher fusion rate compared to the uninstrumented group. The cost analysis suggest that instrumented fusion is cost effective with an ICER of 1536. Concluding that, in treating degenerative spondylolisthesis in the elderly, instrumented fusion would be advisable in patients where fusion is needed. 
Translated title of the contributionInstrumenteret eller uinstrumenteret stivgørende operation som behandling for degenerativt ledskred
Original languageEnglish
Awarding Institution
  • University of Southern Denmark
  • Andersen, Mikkel Østerheden, Principal supervisor
  • Carreon, Leah, Supervisor
  • Sørensen, Jan, Supervisor
  • Rousing, Rikke, Supervisor
Publication statusPublished - 20. May 2022


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