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Clinically Meaningful Improvement Following Cervical Spine Surgery: 30% Reduction Versus Absolute Point-change MCID Values.

STUDY DESIGN
Retrospective analysis of prospectively collected registry data.


OBJECTIVE
The aim of this study was to compare the performance of 30% reduction to established absolute point-change values for measures of disability and pain in patients undergoing elective cervical spine surgery.


SUMMARY OF BACKGROUND DATA
Recent studies recommend using a proportional change from baseline instead of an absolute point-change value to define minimum clinically important difference (MCID).


METHODS
Analyses included 13,179 patients who underwent cervical spine surgery for degenerative disease between April 2013 and February 2018. Participants completed a baseline and 12-month follow-up assessment that included questionnaires to assess disability (Neck Disability Index [NDI]), neck and arm pain (Numeric Rating Scale [NRS-NP/AP], and satisfaction [NASS scale]). Participants were classified as met or not met 30% reduction from baseline in each of the respective measures. The 30% reduction in scores at 12 months was compared to a wide range of established absolute point-change MCID values using receiver-operating characteristic curves, area under the receiver-operating characteristic curve (AUROC), and logistic regression analyses. These analyses were conducted for the entire patient cohort, as well as for subgroups based on baseline severity and surgical approach.


RESULTS
Thirty percent reduction in NDI and NRS-NP/AP scores predicted satisfaction with more accuracy than absolute point-change values for the total population and ACDF and posterior fusion procedures (P < 0.05). The largest AUROC differences, in favor of 30% reduction, were found for the lowest disability (ODI 0-20%: 16.8%) and bed-bound disability (ODI 81%-100%: 16.6%) categories. For pain, there was a 1.9% to 11% and 1.6% to 9.6% AUROC difference for no/mild neck and arm pain (NRS 0-4), respectively, in favor of a 30% reduction threshold.


CONCLUSION
A 30% reduction from baseline is a valid method for determining MCID in disability and pain for patients undergoing cervical spine surgery.Level of Evidence: 3.