Health-related quality of life (HRQOL) measures have become the mainstay for outcome appraisal in spine surgery. Clinically meaningful interpretation of HRQOL improvement has centered on the minimum clinically important difference (MCID). The purpose of this study was to calculate clinically important deterioration (CIDET) thresholds and determine a CIDET value for each HRQOL measure for patients undergoing lumbar fusion.
Seven hundred twenty-two patients (248 males, 127 smokers, mean age 60.8 years) were identified with complete preoperative and 1-year postoperative HRQOLs including the Oswestry Disability Index (ODI), 36-Item Short Form Health Survey (SF-36), and numeric rating scales (0–10) for back and leg pain following primary, instrumented, posterior lumbar fusion. Anchor-based and distribution-based methods were used to calculate CIDET for each HRQOL. Anchor-based methods included change score, change difference, and receiver operating characteristic curve analysis. The Health Transition Item, an independent item of the SF-36, was used as the external anchor. Patients who responded “somewhat worse” and “much worse” were combined and compared with patients responding “about the same.” Distribution-based methods were minimum detectable change and effect size.
Diagnoses included spondylolisthesis (n = 332), scoliosis (n = 54), instability (n = 37), disc pathology (n = 146), and stenosis (n = 153). There was a statistically significant change (p < 0.0001) for each HRQOL measure from preoperatively to 1-year postoperatively. Only 107 patients (15%) reported being “somewhat worse” (n = 81) or “much worse” (n = 26). Calculation methods yielded a range of CIDET values for ODI (0.17–9.06), SF-36 physical component summary (−0.32 to 4.43), back pain (0.02–1.50), and leg pain (0.02–1.50).
A threshold for clinical deterioration was difficult to identify. This may be due to the small number of patients reporting being worse after surgery and the variability across methods to determine CIDET thresholds. Overall, it appears that patients may interpret the absence of change as deterioration.