What is the average time frame of clinically meaningful improvement in surgical decompression for cervical spondylotic myelopathy? A Spine CORe™ analysis of QOD data: 5-year follow-up

OBJECTIVE: The objective of this study was to determine the time frame of clinical improvement in patient-reported outcomes (PROs) following surgical decompression for cervical spondylotic myelopathy (CSM). Based on previously published 12-month data from this group, the authors hypothesized that the average time to minimal clinically important difference (MCID) improvement would primarily occur by 3 months postoperatively regardless of preoperative myelopathy severity. They also hypothesized that there would be minimal additional improvement between 3 months and 5 years after surgery. METHODS: This was a post hoc analysis of prospectively collected data from the 14-site Spine CORe™ study group of the Quality Outcomes Database (QOD). Patients were stratified according to myelopathy severity using the modified Japanese Orthopaedic Association (mJOA) myelopathy scale into mild (mJOA score 15-17), moderate (mJOA score 12-14) or severe (mJOA score < 12). PRO measures included the Neck Disability Index (NDI), numeric rating scale (NRS) for neck and arm pain, and EQ-5D for quality-adjusted life years. PROs were recorded at baseline, 3-month, 12-month, 2-year, and 5-year intervals. MCID thresholds were calculated using previously validated methods in this cohort. Time to meet the MCID cutoff and the proportion of patients achieving MCID at each time point were determined. RESULTS: A total of 1085 patients (with ≥ 80% follow-up at 60 months for all PRO measures [PROMs]) were enrolled. Patients with more severe myelopathy had worse baseline comorbidities (e.g., BMI, American Society of Anesthesiology class, ambulation dependence) and lower PRO scores. Average PROs met the MCID threshold in each category at 3 months postoperatively, regardless of baseline myelopathy severity. Of the patients with complete 5-year follow-up data, the majority achieved the MCID cutoff threshold for PROMs at 3 months (50%-73%, depending on the PROM). A minority of patients went on to meet the MCID for PROMs at 12 months (12%-21%), 2 years (4%-8%), and 5 years (1%-6%). Between 4% and 25% of patients never achieved MCID cutoffs at any time point. CONCLUSIONS: On average, patients achieved clinically meaningful improvement in PROs at 3 months postoperatively, regardless of preoperative severity. While the majority (50%-73%, depending on the PROM) reached MCID within 3 months, an additional 12%-21% improved by 12 months, 4%-8% by 2 years, and only 1%-6% by 5 years; 4%-25% never reach the MCID. This 5-year follow-up study clarifies the timeline of clinical improvement after surgery for CSM and provides a useful tool for both surgeon planning and patient counseling.