2021 ISAKOS Biennial Congress Paper
Creating A Crosswalk For Knee Outcomes After ACLR From The KOOS(5) To The IKDC-SKF
Jessica L. Johnson, DPT, PhD, Minneapolis, MN UNITED STATES
Aaron Boulton, PhD, Newark, DE UNITED STATES
Kurt Paul Spindler, MD, Hillsboro Beach, FL UNITED STATES
Laura J. Huston, MS, Nashville, TN UNITED STATES
Tim Spalding, FRCS(Orth), Leamington Spa, Warwickshire UNITED KINGDOM
Laura Asplin, Coventry UNITED KINGDOM
May Arna Risberg, PT, PhD, Oslo NORWAY
Lynn Snyder-Mackler, PT, ScD, FAPTA, Newark, DE UNITED STATES
University of Delaware, Newark, DE, UNITED STATES
FDA Status Not Applicable
Summary
We created a statistical method to convert KOOS scores to IKDC-SKF scores pre- and post-ACLR using three large datasets to enable more rigorous comparisons and pooling for meta-analysis.
Abstract
The variance of patient reported outcomes measures (PROM) used in both clinical and research practice limits the comparison of outcomes and prevents pooling of data for meta-analysis. Two commonly used PROM in anterior cruciate ligament (ACL) registries and cohorts are the Knee Injury Osteoarthritis Outcomes Survey (KOOS) and International Knee Documentation Committee-Subjective Knee Form (IKDC-SKF), but few studies collect or report both scores. Our objective was to create a statistical method to convert averaged KOOS scores to IKDC-SKF scores to enable more rigorous comparisons and pooling for meta-analysis.
Methods
We used equipercentile equating methods to create a statistical crosswalk in one ACL cohort at three time-points: pre-ACL reconstruction (ACLR) and 24- and 72-months after ACLR; this was validated in two other ACL cohorts at similar time-points: pre-ACLR and 24- and 60-months post-ACLR.
Results
We observed high correlations (r=0.81-0.90), unidimensionality (first to second eigenvalues= 8.7-13.3), and subpopulation invariance (root expected mean squared difference=0.009-0.017). The smallest disagreements between crosswalked and true scores was using the 24-month scores; these had a bias of less than 0.1 standard deviation unit.
Conclusion
Our crosswalk is statistically merited and accurately converts group level average KOOS scores to IKDC-SKF scores. This tool will allow for more comparisons and meta-analyses of outcomes after ACL reconstruction, improving our treatment of and outcomes after ACL injury and reconstruction.