Establishing the Minimal Clinically Important Difference and Substantial Clinical Benefit for the Pain Visual Analog Scale in a Postoperative Hand Surgery Population

BACKGROUND: Although the pain visual analog scale (VAS-pain) is a ubiquitous patient-reported outcome instrument, it remains unclear how to interpret changes in scores. Therefore, our purpose was to calculate the minimal clinically important difference (MCID) and substantial clinical benefit (SCB) for the VAS-pain instrument in a non-shoulder hand and upper extremity postoperative population. METHODS: Adult postoperative patients treated by one of five fellowship-trained orthopaedic hand surgeons at a single tertiary academic medical center were identified. Inclusion required VAS-pain scores at baseline (up to 3 months preoperatively) and follow-up (up to 4 months postoperatively) in addition to a response to a pain-specific anchor question at follow-up. MCID estimates were calculated with 1) the 1/2 standard deviation (SD) method and 2) an anchor-based approach. SCB estimates were calculated with 1) an anchor-based approach and 2) a receiver operator curve (ROC) method that maximized the sensitivity and specificity for detecting a “Much improved” status. RESULTS: A total of 667 and 148 patients were included in the MCID and SCB analyses, respectively. The 1/2 SD MCID estimate was 1.6, and the anchor-based estimate was 1.9. The anchor-based SCB estimate was 2.2. ROC analysis yielded an SCB estimate of 2.6, with an area under the curve of 0.72 consistent with acceptable discrimination. CONCLUSIONS: We propose MCID values in the range of 1.6 to 1.9 and SCB values in the range of 2.2 to 2.6 for the VAS-pain instrument in a non-shoulder hand and upper extremity postoperative population. CLINICAL RELEVANCE: These MCID and SCB estimates may be useful for powering clinical studies, and when interpreting VAS-Pain score changes or differences reported in the hand surgery literature. These values are to be applied at a population level, and should not be applied to assess the improvement, or lack thereof, for individual patients.