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Responsiveness and Minimal Important Changes for the Knee Injury and Osteoarthritis Outcome Score in Subjects Undergoing Rehabilitation After Total Knee Arthroplasty

Monticone, Marco MD, PhD; Ferrante, Simona PhD; Salvaderi, Stefano MD; Motta, Lorenzo MD; Cerri, Cesare MD

American Journal of Physical Medicine & Rehabilitation: October 2013 - Volume 92 - Issue 10 - p 864–870
doi: 10.1097/PHM.0b013e31829f19d8
Original Research Article

Objective The aim of this study was to evaluate the responsiveness and minimal important changes for the Knee Injury and Osteoarthritis Outcome Score (KOOS) in subjects undergoing rehabilitation after total knee arthroplasty.

Design At the beginning and end of a rehabilitation program, 148 patients completed the KOOS. A global perception of change scale was also completed at the end of the program and collapsed to produce a dichotomous outcome (improved vs. stable). Responsiveness was assessed on the KOOS subscales and calculated by distribution methods (effect size; standardized response mean). The minimal important changes of the KOOS subscales were assessed using anchor-based methods (receiver operating characteristic curves) to compute the best cutoff levels between the improved and stable subjects.

Results The effect sizes ranged from 0.83 to 1.35, and the standardized response means ranged from 0.76 to 1.22. The receiver operating characteristic analyses revealed an area under the curve of 0.89, 0.88, 0.94, 0.93, and 0.85 for the Pain, Symptoms, Activities of Daily Living, Sport/Recreation, and Quality of Life subscales, respectively, showing discriminative capacities; the minimal important changes were 16.7 for Pain (sensitivity: 83%; specificity: 82%), 10.7 for Symptoms (80%; 80%), 18.4 for Activities of Daily Living (82%; 82%), 12.5 for Sport/Recreation (96%; 78%), and 15.6 for Quality of Life (88%; 67%).

Conclusions The KOOS was sensitive in detecting clinical changes. The authors recommend taking the minimal important changes provided into account when assessing patient improvement or planning studies in this clinical context.

From the Physical Medicine and Rehabilitation Unit, Scientific Institute of Lissone, Salvatore Maugeri Foundation, Institute of Care and Research (IRCCS) Lissone, Milano, Italy (MM, SF, SS); Neuroengineering and Medical Robotics Laboratory, Dipartimento di Elettronica, Informazione e Bioingegneria, Politecnico di Milano, Milano, Italy (SF); School of Physical Medicine and Rehabilitation, “Bicocca” University of Milan, Milano, Italy (LM, CC).

All correspondence and requests for reprints should be addressed to: Marco Monticone, MD, PhD, Physical Medicine and Rehabilitation Unit, Scientific Institute of Lissone, Salvatore Maugeri Foundation, Institute of Care and Research (IRCCS), Via Monsignor Bernasconi 16, 20035 Lissone Milano, Italy.

Abstract previously published in the National Congress of the Italian PMR Schools meeting program, 2012 edition.

Financial disclosure statements have been obtained, and no conflicts of interest have been reported by the authors or by any individuals in control of the content of this article.

© 2013 by Lippincott Williams & Wilkins