Linking the KOOS-PS to PROMIS Physical Function in Knee Patients Evaluated for Surgery

Introduction:The Knee Injury and Osteoarthritis Outcome Score-Physical Function Short-form and the Patient-Reported Outcomes Measurement Information System Physical Function are widely used patient-reported outcome measures in orthopaedic practice and research. It would be helpful for clinicians and researchers to compare scores obtained on one instrument with those collected on another. To achieve this goal, this study conducted a linking analysis and computed a crosswalk table between these two scales.Data:The data of this study were collected as part of the clinical care of total knee arthroplasty patients in a large urban and suburban health system. The sample was a mix of responses from nonsurgical (no surgery performed), preoperative (before surgical intervention), and postoperative (after surgical intervention) groups.Methods:This study applied five linking methods: the item response theory (IRT)-based linking methods including fixed-parameter calibration, separate-parameter calibration with Stocking-Lord constants, and calibrated projection; and the equipercentile methods with log-linear smoothing and nonsmoothing approaches. Before conducting the linking analysis, we checked the linking assumptions including the similar content of the two scales, the unidimensionality of the combined scales, and the population invariance. The results of the five linking methods were evaluated by mean difference, SD, root-mean-squared deviation, intraclass correlation coefficient of the observed T scores and the crosswalk-derived T scores.Results:The linking assumptions were all met. T scores generated from the Stocking-Lord crosswalk had the smallest mean difference (= -0.03) and relatively small SD (= 4.91) and root-mean-squared deviation (= 4.91) among the five linking methods. We validated this crosswalk in a larger sample with the nonsurgical, preoperative, and postoperative groups and in an external sample.Discussion:This study provides clinicians and researchers a practical tool (ie, a crosswalk table) to link scores from two popular physical function measures. Given the diversity of patient-reported outcome measures in use for knee conditions, these crosswalk tables would accelerate clinical and research interpretation of aggregating functional outcomes among the patients evaluated for knee surgery each year.