Is there discordance between achieving the minimal clinically important difference in Neck Disability Index score and patient satisfaction after surgery for cervical spondylotic myelopathy? A Spine CORe™ 5-year analysis of QOD data

OBJECTIVE: Minimal clinically important difference (MCID) thresholds are widely used to evaluate outcomes after surgery for cervical spondylotic myelopathy (CSM), but they may not fully reflect patient satisfaction. The authors hypothesized that discordance exists between MCID achievement in Neck Disability Index (NDI) score and satisfaction at long-term follow-up in a minority of patients after surgery for CSM. METHODS: The 14-site Spine CORe™ study group performed a post hoc analysis of their prospectively collected data from the Quality Outcomes Database, which included 1085 patients who underwent surgery for CSM. Patients with complete baseline and 5-year NDI scores as well as 5-year satisfaction data were included. Satisfaction was assessed using the North American Spine Society (NASS) satisfaction index, and the MCID was defined for the NDI score. Baseline characteristics and patient-reported outcomes were compared between satisfied and dissatisfied patients within the cohort who met the MCID for NDI score. Multivariate logistic regression identified predictors of dissatisfaction despite the MCID. RESULTS: In total, 1085 patients underwent surgery for CSM. The 5-year follow-up rate was 82% (106 died within 5 years, and 782 had both 5-year satisfaction and NDI data). At 5 years postoperatively, 497 patients (63.6%) achieved the MCID in NDI score. Among MCID achievers, 463 (93%) were satisfied and 34 (7%) were not satisfied. On univariate analysis, of those who met the MCID, dissatisfied patients were more likely to be current smokers (32.4% vs 15.8%, p = 0.029) and less likely to participate in outside activities (58.8% vs 85.1%, p < 0.001). They also presented with greater baseline disability (NDI score: 47.9 ± 18.2 vs 41.1 ± 19.5, p = 0.021), lower quality of life (EQ-5D score: 0.50 ± 0.19 vs 0.58 ± 0.22, p = 0.029), and lower preoperative functional status (mJOA score: 11.2 ± 2.8 vs 12.3 ± 2.7, p = 0.025) compared with satisfied patients. On multivariate analysis, of those who met the MCID, smoking showed a trend toward higher odds of dissatisfaction (OR 2.12, p = 0.065), while participation in outside activities was protective (OR 0.28, p < 0.001). CONCLUSIONS: In this study, only 7% of patients were dissatisfied despite achieving the MCID for NDI score. Participation in outside activities was independently associated with greater satisfaction, whereas smoking showed a trend toward increased dissatisfaction despite meeting the MCID for NDI score. The MCID and satisfaction capture distinct yet complementary aspects of recovery and should be jointly considered during preoperative counseling and postoperative outcome assessment.