What Is the Most Appropriate Method for Determining Minimally Clinical Important Difference in Grade 2 Spondylolisthesis? A QOD Spine CORe® Study

BACKGROUND AND OBJECTIVES: Minimally clinically important difference (MCID) defines the smallest difference in patient-reported outcomes (PROs) required for a level of clinical improvement. The hypothesis of this study is that at least one of the MCID thresholds in this study will provide appropriate MCID thresholds for the PROs in grade 2 spondylolisthesis. METHODS: This study used the Grade 2 Spondylolisthesis module of the Quality Outcomes Database Spine CORe® Study Group, which included 328 patients from 14 institutions. PROs collected include Oswestry Disability Index (ODI), Numeric Rating Scale (NRS) for back pain and leg pain, and European Quality of Life-5 Dimensions (EQ-5D). Seven MCID thresholds were calculated with North American Spine Society satisfaction scale as the anchor. Each method was evaluated using area under the curve, reflecting the ability to predict satisfaction. RESULTS: There were 328 patients with ≥80% 5-year follow-up. The optimal percentage cutoff method generally demonstrated the highest predictive accuracy for defining MCID in ODI, NRS back pain, and NRS leg pain, whereas the optimal numeric cutoff method generally demonstrated the highest predictive accuracy for EQ-5D. For ODI, 2-year optimal percentage cutoff was 30.4% and 5-year optimal percentage cutoff was 38.1%. For NRS back pain, 2-year optimal percentage cutoff was 75.0% and 5-year optimal percentage cutoff was 42.9%. For NRS leg pain, 2-year optimal percentage cutoff was 62.5% and 5-year optimal percentage cutoff was 66.6%. For EQ-5D, the optimal numeric cutoffs were 0.293 at 2 years and 0.128 at 5 years. CONCLUSION: Using satisfaction as an anchor, this study identified the optimal percentage cutoff as the most appropriate method for determining MCID in ODI and NRS pain scores, while the optimal numeric cutoff was most appropriate for EQ-5D in grade 2 spondylolisthesis. These findings provide reference definitions for evaluating postoperative improvement in this patient population.