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

Abstract

Although the pain visual analog scale (VAS-pain) is a ubiquitous patient-reported outcome instrument, it remains unclear how to interpret changes or differences 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 nonshoulder hand and upper extremity postoperative population. Adult postoperative patients treated by 1 of 5 fellowship-trained orthopedic hand surgeons at a single tertiary academic medical center were identified. Inclusion required VAS-pain scores at baseline (up to 3 months before surgery) and follow-up (up to 4 months after surgery), in addition to a response to a pain-specific anchor question at follow-up. The MCID estimates were calculated with (1) the 1/2 standard deviation method; and (2) an anchor-based approach. The SCB estimates were calculated with (1) an anchor-based approach; and (2) a receiver operator curve method that maximized the sensitivity and specificity for detecting a "much improved" pain status. There were 667 and 148 total patients included in the MCID and SCB analyses, respectively. The 1/2 standard deviation MCID estimate was 1.6, and the anchor-based estimate was 1.9. The anchor-based SCB estimate was 2.2. The receiver operator curve analysis yielded an SCB estimate of 2.6, with an area under the curve of 0.72, consistent with acceptable discrimination. 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 nonshoulder hand and upper extremity postoperative population. 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.