Classifications of good versus poor outcome following knee arthroplasty should not be defined using arbitrary criteria
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(2020) 21:604
CORRESPONDENCE
Open Access
Classifications of good versus poor outcome following knee arthroplasty should not be defined using arbitrary criteria Daniel L. Riddle1*
and Levent Dumenci2
Abstract A recently published paper by te Molder and colleagues in BMC Musculoskeletal Disorders confirmed prior reports indicating that definitions of good versus poor outcome cutoff scores for relevant knee arthroplasty outcomes including pain and function are heterogeneous and that this heterogeneity prevents generalizable inferences. In this Correspondence, we highlight an additional and, in our view, a more important problem with the substantial literature on this topic. There also is high homogeneity in that all studies relied on arbitrarily defined cutoff scores to differentiate good versus poor outcome. We discuss this problem and propose a method to avoid repeating the same problem in future studies designed to group patients into those with good versus those with poor outcome following knee arthroplasty. Keywords: Knee, arthroplasty, outcome, pain, function
Main text The systematic review by te Molder and colleagues [1] summarized various methods used by investigators to dichotomize outcomes of patients with knee arthroplasty (KA) as either good or poor. There are important reasons for wanting to know if a patient’s KA outcome is good or poor. For example, interventions to improve outcome can be specifically designed and targeted to patients fitting the poor outcome phenotype. The dilemma with categorizing outcome, as te Molder et al. and others [2, 3] have noted, is that definitions of good versus poor outcome vary substantially across the many studies that have attempted to categorize outcomes following KA. * Correspondence: [email protected] 1 Departments of Physical Therapy, Orthopaedic Surgery and Rheumatology, Virginia Commonwealth University, Richmond, VA, USA 2 Department of Epidemiology and Biostatistics, 1301 Cecil B. Moore, Ave., Ritter Annex, Room 939, Temple University, Philadelphia, PA 19122, USA
Variation precludes consensus and prevents meaningful comparisons across study cohorts. We noted an additional problem with evidence classifying outcome as good or poor [4]. Definitions of good versus poor outcome are grounded in the use of arbitrary cutoff values, whether based on final outcome score, percent or absolute change from baseline or the Minimal Clinically Important Difference (MCID) family of change indicators. The main conclusion of the study by te Molder and colleagues was that there was substantial heterogeneity in the 47 definitions of good versus poor KA outcomes. In our view, te Molder et al. should also have focused on implications related to the homogeneity of these 47 definitions. All studies in the review used the cutoff method to determine good versus poor outcome. Cutoff scores are, by definition, arbitrary. Supplemental file 3 in the study by te Molder et al.
© The Author(s). 2020 Open Access This article is licensed under a Creative Commons Attribution 4.0 International
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