Cross-cultural adaptation and psychometric validation of the Dutch version of the Core Outcome Measures Index for the back (COMI -back) in patients undergoing surgery for degenerative disease of the lumbar spine

Introduction: Patient-reported outcome measures (PROMs) are the preferred outcomes measured in patients with lumbar spinal degenerative diseases. As PROMs can be lengthy and therefore pose a burden to patients and re-searchers, short and standardized PROMs are needed, such as the Core Outcome Measures Index (COMI). Research question: Is the Dutch version of the COMI-back a reliable and responsive PROM to measure outcomes in lumbar degenerative spinal surgery?Methods: After translating and cross-cultural adapting the COMI-back into Dutch, patients who were on the waiting-list for lumbar decompression surgery in a secondary referral center, were enrolled in the validation study. Patients completed a baseline booklet consisting of the COMI-back, likert scales measuring back and leg pain, the Roland-Morris Disability questionnaire, the EuroQoL-5 dimensions and the WHO-Quality-of-Life-BREF questionnaire to test construct validity. Within 2 weeks and before undergoing surgery, patients completed the COMI-back again, to measure test-retest stability. Three months after surgery, a global treatment outcome (GTO) question and the COMI-back were completed to test responsiveness.Results: The COMI-back was successfully translated and adapted into Dutch. One-hundred-thirty-five patients completed the baseline booklet, 93 the test-retest questionnaire and 102 the responsiveness questionnaire. The COMI-summary score and four of five COMI-domains, showed good to very good correlation to the reference questionnaires (& rho; > 0.41). The COMI-back showed a good test-retest stability with an intraclass correlation co-efficient of 0.81 for the summary score. Furthermore, the standard error of agreement was 0.65 and the minimal detectable change was 1.8 points. The ROC-curve showed an area under the curve of 0.89 (95% CI 0.82 to 0.95). Conclusion: The Dutch version of the COMI-back has satisfactory psychometric properties and is a reliable and responsive patient-reported outcome measure in patients undergoing surgery for lumbar degenerative disease.