Minimal important improvement thresholds for the six-minute walk test in a knee arthroplasty cohort: triangulation of anchor- and distribution-based methods

Abstract

BackgroundThe 6-minute walk test (6MWT) is a commonly used metric for measuring change in mobility after knee arthroplasty, however, what is considered an improvement after surgery has not been defined. The determination of important change in an outcome assessment tool is controversial and may require more than one approach. This study, nested within a combined randomised and observational trial, aimed to define a minimal important improvement threshold for the 6MWT in a knee arthroplasty cohort through a triangulation of methods including patient-perceived anchor-based thresholds and distribution-based thresholds.MethodsIndividuals with osteoarthritis performed a 6MWT pre-arthroplasty then at 10 and 26 weeks post-surgery. Each rated their perceived improvement in mobility post-surgery on a 7-point transition scale anchored from “much better” to “much worse”. Based on these responses the cohort was dichotomised into ‘improved’ and ‘not improved’. The thresholds for patient-perceived improvements were then identified using two receiver operating curve methods producing sensitivity and specificity indices. Distribution-based change thresholds were determined using two methods utilising effect size (ES). Agreement between the anchor- and distribution-based methods was assessed using kappa.ResultsOne hundred fifty-eight from 166 participants in the randomised cohort and 222 from 243 in the combined randomised and observational cohort were included at 10 and 26 weeks, respectively. The slightly or more patient-perceived improvement threshold at 26 weeks (an absolute improvement of 26 m) was the only one to demonstrate sensitivity and specificity results both better than chance. At 10- and 26-weeks, the ES based on the mean change score divided by the baseline standard deviation (SD), was an absolute change of 24.5 and 37.9 m, respectively. The threshold based on a moderate ES (a 0.5 SD of the baseline score) was a change of 55.0 and 55.4 m at 10- and 26-weeks, respectively. The level of agreement between the 26-week anchor-based and distribution-based minimal absolute changes was very good (k = 0.88 (95 % CI 0.81 0.95)).ConclusionA valid threshold of improvement for the 6MWT can only be proposed for changes identified from baseline to 26 weeks post-surgery. The level of agreement between anchor- and distribution-based methods indicates that a true minimal or more threshold of meaningful improvement following surgery is likely within the ranges proposed by the triangulation of all four methods, that is, 26 to 55 m.

Improved walking distance and range of motion predict patient satisfaction after TKA

“…This cut-off value is similar to the results of Naylor et al who described the threshold of improvement for the 6MWT, at 26 weeks post TKA, between 26 and 55 m [33]. While they used a 7-point transition scale of improvement, we used the aforementioned clusters to define the threshold.…”

Assessment of Outcomes of Inpatient or Clinic-Based vs Home-Based Rehabilitation After Total Knee Arthroplasty

“…However, research indicates that this difference is not clinically important. Using a triangulation of methods, including patient-perceived anchor-based thresholds and distribution-based thresholds, Naylor and colleagues 41 proposed that the threshold for minimal or more improvement for the 6MWT after TKA is expected to range from 26 to 55 m. For patients with chronic obstructive pulmonary disease, Rasekaba and colleagues 42 determined the minimal clinically important distance for the 6MWT is 54 m, with a similar figure (50 m) determined for a population of older adults and those with stroke by Perera et al 43 …”

A Combination of Tamarindus indica seeds and Curcuma longa Rhizome Extracts Improves Knee Joint Function and Alleviates Pain in Non-Arthritic Adults Following Physical Activity

“…The SMWT is a simple, validated and reliable physical test to evaluate improvement in musculoskeletal functions 24,34. SMWT measures submaximal functional performance 35 and assesses a senior person's fitness as part of the LifeSpan Wellness Program 36.…”