Validity and responsiveness of the Core Outcome Measures Index (COMI) for the neck

Patient-orientated outcome questionnaires are essential to evaluate treatment success. To compare different treatments, hospitals, and surgeons, standardised questionnaires are required. The present study examined the validity and responsiveness of the Core Outcome Measurement Index for neck pain (COMI-neck), a short, multidimensional outcome instrument.

Questionnaires were completed by patients with degenerative problems of the cervical spine undergoing cervical disc arthroplasty before (N = 89) and 3 months after (N = 75) surgery. The questionnaires comprised the EuroQol-Five Dimension (EQ-5D), the North American Spine Society Cervical Spine Outcome Assessment Instrument (NASS-cervical) and the COMI-neck.

The COMI and NASS-cervical scores displayed no notable floor or ceiling effects at any time point whereas for the EQ-5D, the highest values [corrected] were reached in around 32.5% of patients at follow-up. With one exception (symptom-specific well-being), the individual COMI items and the COMI summary score correlated to the expected extent (R = 0.4-0.8) with the scores of the chosen reference questionnaires. The area under the curve (AUC) generated by ROC analysis was significantly higher for the COMI (0.96) than for any other instrument/subscale when self reported treatment outcome was used as the external criterion, dichotomised as "good" (operation helped a lot/helped) versus "poor" (operation helped only a little/didn't help/made things worse). The COMI had a high effect size (standardised response mean; SRM) (2.34) for the good global outcome group and a low SRM for the poor outcome group (0.34). The EQ-5D and the NASS-cervical lacked this ability to differentiate between the two groups, showing less distinct SRMs for good and poor outcome groups.

This study provides evidence that the COMI-neck is a valid and responsive questionnaire in the population of patients examined. Further investigations should examine its applicability in other patient groups with less severe neck pain or undergoing other treatment modalities.