Evaluating Psychometric Properties of the International Knee Documentation Committee Subjective Knee Form in a Heterogeneous Sample of Post-Operative Patients

BACKGROUND: The International Knee Document Committee Subjective Knee Form (IKDC-SKF) is a patient-reported outcome measure used in orthopedics and sports medicine. Further psychometric assessment is necessary to confirm measurement properties in a large, heterogenous sample. PURPOSE: The purpose of the study was to assess the psychometric properties of the IKDC-SKF in a large, heterogenous sample. STUDY DESIGN: Cross-Sectional Study METHODS: An exploratory factor analysis (EFA) was conducted to identify a sound latent structure and to assess internal consistency in a large sample of patients who underwent knee arthroscopy. A confirmatory factor analysis (CFA) was conducted to confirm structural validity. Multi-group invariance was conducted to assess factorial stability across sex and age groups, while longitudinal invariance procedures were performed to assess stability over time. RESULTS: A 3-factor, 9-item IKDC-SKF short form was identified with EFA procedures. The model was confirmed with CFA (CFI = 0.983; TLI = 0.975; IFI = 0.983; RMSEA = 0.057), while a sound 2-factor, 6-item model was also identified (CFI = 1.0; TLI = 0.999; IFI = 1.0; RMSEA = 0.11). The 9-item IKDC-SKF short form was invariant across groups but not time; removal of a single item (i.e., 8-item IKDC-SKF short form) resulted in longitudinal invariance. The 6-item IKDC-SKF short form was invariant across groups and time. CONCLUSION: The 6-item, 8-item, and 9-item short form versions of the IKDC-SKF exceed contemporary fit recommendations and present as plausible alternatives to the IKDC-SKF with improved measurement properties, reduced scale response burden, and evidence of multi-group and longitudinal invariance. Further, the 6- and 8-item IKDC-SKF short forms may be used to assess group differences or change across time. # Level of evidence here Level 3