Validity of the Japanese Core Outcome Measures Index (COMI)-Back for thoracic and lumbar spine surgery: a prospective cohort study.

Purpose: To investigate the psychometric properties of the Japanese version of the Core Outcome Measures Index-Back (COMI-Back), only recently published according to the established linguistic and cultural conversion guidelines, in patients undergoing spine surgery.

Methods: We recruited 145 patients who underwent thoracic or lumbar spine surgery in one of the five specific tertiary care institutions. They were asked to complete a booklet questionnaire (the COMI-Back, the Numerical Rating Scale for pain, the Short Form-12, Euro-QOL-5 dimensions, and Oswestry Disability Index) at baseline and 12 months postoperatively to investigate floor/ceiling effect, construct validity, and postoperative responsiveness. The patients were also asked to answer an anchor question (Global Treatment Outcome) to analyze the minimum clinically important difference (MCID) by receiver operating characteristics curves. Of the 145 patients, 112 completed the study. Another group of 59 volunteers with chronic symptoms completed the questionnaire twice within a 7-14-day interval for the test-retest reproducibility.

Results: The COMI summary score displayed no notable floor or ceiling effects. Except for symptom-specific well-being, the individual COMI domains and the COMI summary score correlated as expected with the scores of the chosen reference measures (ρ = 0.4-0.8). A similar trend was observed between the pre-/postoperative changes in the COMI score and those in the reference measures. The MCID for the COMI summary score was 2.5. The intraclass correlation coefficient and minimum detectable change (MDC95%) were 0.93 and 1.26, respectively.

Conclusion: The Japanese COMI-Back was a reliable and responsive questionnaire in our Japanese patients undergoing thoracic/lumbar spine surgery. These slides can be retrieved under Electronic Supplementary Material.