Minimal Clinically Important Difference and Substantial Clinical Benefit Values for a Pain Visual Analog Scale After Hip Arthroscopy

Abstract

To define minimal clinically important difference (MCID) and substantial clinical benefit (SCB) values for a pain visual analog scale (VAS) in patients undergoing hip arthroscopy for femoroacetabular impingement or chondrolabral pathology. This was a retrospective review of prospective collected data on patients having hip arthroscopy for femoroacetabular impingement and/or chondrolabral pathology. On initial assessment and follow-up between 335 and 395days postsurgery, subjects completed a pain VAS and categorical self-rating of function. MCID was calculated using one-half the standard deviation (SD) of the change in 1-year pain VAS values. Receiver operator characteristic analysis was performed to determine SCB values. A change in SCB value was determined based on change in categorical self-rating of function to create "improved" and "not improved" groups. Absolute postoperative SCB scores were calculated to determine scores that would be associated with "normal" or "abnormal" function ratings. Of 1,034 eligible patients, 733 (71%) met the inclusion criteria, with 537 (73%) women and 196 (27%) men having a mean age of 35.3years (SD 13). At a mean of 352 (SD 21) days postsurgery, 536 (73%) were in the improved group and 197 (27%) in the not improved group. MCID was -15.0mm. A change of -22.7mm on the pain VAS was able to identify those that improved with high sensitivity (0.74) and specificity (0.63). Values of ≤10.4mm and ≥29.0mm were cutoffs identifying subjects that rated their function as normal or abnormal, respectively, with high sensitivity (0.79 and 0.76) and specificity (0.88 and 0.76). This study provides surgeons with information to help interpret pain VAS values at a follow-up period ranging from 335 to 395days with MCID and SCB values of -15.0mm and -22.7mm, respectively. Additionally, a patient who assesses a pain level at ≤10.4mm is likely to have a normal rating of function, whereas a patient who assesses a pain level at ≥29.0mm is likely to have an abnormal rating of function. III, retrospective comparative study.