Measuring clinically relevant improvement after lumbar spine surgery: is it time for something new?

Background Context: Minimum clinically important difference (MCID) for patient-reported outcome measures is commonly used to assess clinical improvement. However, recent literature suggests that an absolute point-change may not be an effective or reliable marker of response to treatment for patients with low or high baseline patient-reported outcome scores. The multitude of established MCIDs also makes it difficult to compare outcomes across studies and different spine surgery procedures.
Purpose: To determine whether a 30% reduction from baseline in disability and pain is a valid method for determining clinical improvement after lumbar spine surgery.
Study Design: Retrospective analysis of prospective data from a national spine registry, the Quality Outcomes Database.
Patient Sample: There were 23,280 participants undergoing elective lumbar spine surgery for degenerative disease who completed a baseline and follow-up assessment at 12 months.
Outcome Measures: Patient-reported disability (Oswestry Disability Index [ODI]), back and leg pain (11-point Numeric Rating Scale [NRS]), and satisfaction (NASS scale).
Methods: Patients completed baseline and a 12-month postoperative assessment to evaluate the outcomes of disability, pain, and satisfaction. The change in ODI and NRS pain scores was categorized as met (≥30%) or not met (<30%) percent reduction MCID. The 30% reduction from baseline was compared with a wide range of well-established absolute point-change MCID values. The relationship between 30% reduction and absolute change values and satisfaction were primarily compared using receiver operating characteristic (ROC) curves, area under the curve (AUROC), and logistic regression analyses. Analyses were conducted for overall scores and for disability and pain severity categories and by surgical procedure.
Results: Thirty percent reduction in ODI and back and leg pain predicted satisfaction with more accuracy than absolute point-change values for the total population and across all procedure categories (p<.001), except for when compared with the highest absolute point-change threshold for leg pain (3.5-point reduction). The largest AUROC differences, in favor of 30% reduction, were found for the lowest disability (ODI 0-20%: 21.8%) and bed-bound disability (ODI 81%-100%: 13.9%) categories. For pain, there was a 3.4%-12.4% and 1.3%-9.8% AUROC difference for no/mild back and leg pain (NRS 0-4), respectively, in favor of a 30% reduction threshold.
Conclusions: A 30% reduction MCID either outperformed or was similar to absolute point-change MCID values. Results indicate that a 30% reduction (baseline to 12 months after surgery) in disability and pain is a valid method for determining clinically relevant improvement in a broad spine surgery population. Furthermore, a 30% reduction was most accurate for patients in the lowest and highest disability and lowest pain severity categories. A 30% reduction MCID allows for a standard cut-off for disability and pain that can be used to compare outcomes across various spine surgery procedures.
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