OBJECTIVE The visual analog scale (VAS) is frequently used to measure treatment outcome in patients with cervical spine disorders. The minimum clinically important difference (MCID) is the smallest change in a score that has clinical importance to the patient. Although it has been established for other medical fields, knowledge of the VAS MCID for the cervical spine is sparse, and it has rarely been considered in relation to measurement noise. The goals in this study were as follows: 1) to validate the VAS-neck and VAS-arm instruments for the cervical spine (e.g., repeatability); 2) to investigate the possible influence of predictive factors and the Hospital Anxiety and Depression Scale (HADS) score on repeatability; and 3) to compute the MCID with 5 different methods. METHODS A post hoc analysis of a prospective randomized controlled trial with 151 patients undergoing surgery for cervical radiculopathy due to degenerative disc disease was performed. Information on age, sex, smoking habits, exercise, employment status, HADS score, and VAS-neck and VAS-arm scores was gathered before surgery and after 1 year. The VAS was applied twice on every occasion, with 15 minutes in between. Repeatability and the association with predictors and HADS score were analyzed using the 1-sample t-test, linear regression models, and Spearman correlation. The MCID was calculated with the following methods: average change, change difference, receiver operating characteristic curve, effect size, and minimum detectable change (MDC). RESULTS The repeatability in VAS-neck was 8.1 mm, and in VAS-arm it was 10.4 mm. Less consistent values on the VAS correlated to female sex and higher values on the HADS. For VAS-neck the MCID ranged from 4.6 to 21.4, and for VAS-arm it ranged from 1.1 to 29.1. The highest MCID came from the MDC method, which was the only method that gave values above the measurement noise in both VAS-neck and VAS-arm. CONCLUSIONS Measurement noise in VAS-neck and VAS-arm for the cervical spine was influenced by female sex and HADS score. The only method to compute MCID that consistently gave results above the measurement noise in VAS-neck and VAS-arm was the MDC. Clinical trial registration no.: 44347115 ( www.isrctn.com ).
Keywords: CI = confidence interval; DDD = degenerative disc disease; HADS = Hospital Anxiety and Depression Scale; Hospital Anxiety and Depression Scale; MCID = minimum clinically important difference; MDC = minimum detectable change; PROM = patient-reported outcome measures; ROC = receiver operating characteristic; SD = standard deviation; SEM = standard error of measurement; VAS = visual analog scale; cervical degenerative disc disease; minimum clinically important difference; surgical treatment; visual analog scale.