Minimum Clinically Important Difference: Current Trends in the Orthopaedic Literature, Part II: Lower Extremity
Authors: Copay Anne G. , Eyberg Blake , Chung Andrew S. , Zurcher Kenneth S. , Chutkan Norman , Spangehl Mark J. 
Published: August 2018

Background:
The minimum clinically important difference (MCID) attempts to define the patient’s experience of treatment outcomes. Efforts at calculating the MCID have yielded multiple and inconsistent MCID values. The purposes of this review were to describe the usage of the MCID in the most recent orthopaedic literature, to explain the limitations of its current uses, and to clarify the underpinnings of the MCID calculation, so as to help practitioners to understand and utilize the MCID and to guide future efforts to calculate the MCID. In Part I of this review, we sampled the orthopaedic literature in relation to the upper extremity. In this part, Part II, of the review, we will focus on the lower-extremity literature.

Methods:
A review was conducted of the 2014 to 2016 MCID-related publications in The Journal of Arthroplasty, The Journal of Bone & Joint Surgery, The American Journal of Sports Medicine, Foot & Ankle International, Journal of Orthopaedic Trauma, Journal of Pediatric Orthopaedics, and Journal of Shoulder and Elbow Surgery. Only clinical science articles utilizing patient-reported outcome measures (PROMs) were included in the analysis. A keyword search was then performed to identify articles that used the MCID. Articles were then further categorized into upper-extremity and lower-extremity publications. The MCID utilization in the selected articles was characterized and was recorded.

Results:
The MCID was referenced in 129 (7.5%) of 1,709 clinical science articles that utilized PROMs: 79 (61.2%) of the 129 articles were related to the lower extremity; of these, 11 (13.9%) independently calculated the MCID values and 68 (86.1%) used previously published MCID values as a gauge of their own results. The MCID values were calculated or were considered for 31 PROMs, of which 24 were specific to the lower extremity. Eleven different methods were used to calculate the MCID. The MCID had a wide range of values for the same questionnaires, for instance, 5.8 to 31.3 points for the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC).

Conclusions:
There are more than twice as many PROMs for the lower extremity (24) than for the upper extremity (11), confirming that the determination of useful MCID values is, in part, hampered by the proliferation of PROMs in the field of orthopaedics. The difference between significance and clinical importance needs to be further clarified. For instance, the common use of determining sample size with the MCID and comparing group means with the MCID implies that a significant result will also be clinically important. Further, the study of the MCID would benefit from consensus agreement on relevant terminology and the appropriate usage of the MCID determining equations.

Clinical Relevance:
MCID is increasingly used as a measure of patients’ improvement. However, MCID does not yet adequately capture the clinical importance of patients’ improvement.