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Understanding crossovers and potential ways to mitigate the problem: Lessons from influential trials on lumbar
V K Y Chan1, T E Darsaut1, C S Bailey2
1Division of Neurosurgery, Department of Surgery, Mackenzie Health Sciences Centre, University of Alberta Hospital, 8440 112, Street NW, Edmonton, Alberta, Canada.
Background:
Lumbar microdiscectomy is the most frequent surgical intervention used in the treatment of sciatica from herniated lumbar discs. Many discectomy trials have been plagued with an excessive number of crossovers that have rendered results inconclusive.
Methods:
We review the design and results of influential lumbar microdiscectomy trials. We also discuss the various strategies that have been used to decrease the number of crossovers or to mitigate the effects of crossovers on analyses.
Results:
Randomized trials on lumbar discectomy were affected by crossover rates of 8% to 42%. Various strategies that have been used to decrease that number or to mitigate the effects on results include: patient selection, blinding (placebo-controlled trials), an immediate access to surgery for the surgical group (but limited access to surgery for the conservative group), shortening the follow-up period necessary to reach the primary outcome measure, postponing crossovers to surgery after determination of the primary outcome, and modifying the primary outcome measure to include treatment failures. Crossovers should be anticipated and compensated for by increasing the number of participants.
Conclusion:
Non-adherence to randomly allocated management options can deprive trials of the statistical power needed to inform clinical care. Crossovers and ways to mitigate related problems should be anticipated at the time of trial design.
