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

Abstract

Purpose: 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. Methods: 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 395 days 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. Results: Of 1,034 eligible patients, 733 (71%) met the inclusion criteria, with 537 (73%) women and 196 (27%) men having a mean age of 35.3 years (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 –15.0 mm. A change of –22.7 mm on the pain VAS was able to identify those that improved with high sensitivity (0.74) and specificity (0.63). Values of ≤10.4 mm and ≥29.0 mm 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). Conclusions: This study provides surgeons with information to help interpret pain VAS values at a follow-up period ranging from 335 to 395 days with MCID and SCB values of –15.0 mm and –22.7 mm, respectively. Additionally, a patient who assesses a pain level at ≤10.4 mm is likely to have a normal rating of function, whereas a patient who assesses a pain level at ≥29.0 mm is likely to have an abnormal rating of function. Level of Evidence: III, retrospective comparative study.