RESUMEN
STUDY DESIGN: Cohort study. OBJECTIVE: To evaluate heterogeneity (fluctuation) in minimal important change (MIC) and patient acceptable symptom state (PASS) for patient-reported outcomes (PROMs) through 10 years after lumbar fusion. SUMMARY OF BACKGROUND DATA: PROMs have become key determinants in spine surgery outcomes studies. MIC and PASS were established to aid PROM interpretations. However, their long-term stability has not yet been reported. METHODS: A consecutive series of elective lumbar fusions were followed-up using the Oswestry Disability Index (ODI) and Visual Analogue Scale (VAS) for pain. Improvement was rated by a 4-point Likert scale into "improved" or "non-improved". Satisfaction-to-treatment was rated by the patients' willingness to undergo surgery again. Receiver operating characteristics (ROC) curve analysis estimated MIC (95% confidence interval, CI) as the PROM change that best predicted improvement at distinct time-points. PASS (CI) was estimated as the lowest PROM score at which the patients were still satisfied. Heterogeneity across thresholds was evaluated using the DeLong algorithm. RESULTS: MIC for ODI represented heterogeneity across 10-years, ranging from -21 (-24 to -16) at 2-years to -8 (-7 to -4) at 5-years, P <0.001. The areas under the ROC curves (AUCs) (0.79-0.85) indicated acceptable to excellent discrimination. Heterogeneity was not significant in the MICs for the pain scores. At 1-year, MIC for back pain was -24 (-38 to -15), AUC 0.77, and for leg pain it was -26 (-44 to -8), AUC 0.78. No significant heterogeneity was observed in 10-year PASS scores. At 1-year, PASS for ODI was 22 (15 to 29), AUC 0.85. Similarly, 1-year PASS for back pain was 38 (20 to 56), AUC 0.81, and for leg pain it was 49 (26 to 72), AUC 0.81. CONCLUSIONS: MIC for ODI fluctuated over 10-years after lumbar fusions. PASS values for all PROMs seemed most stable over time. Caution is needed when generic MIC values are used in long-term studies. LEVEL OF EVIDENCE: Therapeutic Level III.
