What does/should the minimum clinically important difference measure? A reconsideration of its clinical value in evaluating efficacy of lumbar fusion surgery

Objectives: The Minimum Clinical Important Difference (MCID) was initially intended to provide outcome measures that would be more clinically meaningful than measurements based simply on mean improvement in some outcomes. Indeed, a basic concept behind the MCID was that statistically significant differences in measures did not necessarily reflect clinically meaningful benefits. Methods: This study provides a review of the literature suggesting that the MCID metric is not being applied and interpreted in practice in a manner that realizes its potential. The MCID has often been used as a means of delineating whether patients are "feeling better." This does not, though, necessarily indicate that they are "doing better" in terms of physical or socioeconomic functioning. Results: The imperfect correlation between "feeling" and "doing" better makes it difficult to interpret the clinical implications of articles using MCID measures, particularly in the lumbar spine fusion literature. Alternative and more scientifically rigorous approaches to the MCID are presented. Discussion: A call is made for a more comprehensive approach to synthesize a nearly decade's worth of clinical research that has still not yielded consensus concerning the best MCID approach to objectively document lumbar spine fusion patients' outcomes.