Statistical Comparison of the Pediatric Versus Adult IKDC Subjective Knee Evaluation Form in Adolescents

Abstract

Background: The International Knee Documentation Committee (IKDC) Subjective Knee Evaluation Form is a patient-reported outcome with adult (1998) and pediatric (2011) versions validated at different ages. Prior longitudinal studies of patients aged 13 to 17 years who tore their anterior cruciate ligament (ACL) have used the only available adult IKDC, whereas currently the pediatric IKDC is the accepted form of choice. Purpose/Hypothesis: This study compared the adult and pediatric IKDC forms and tested whether the differences were clinically significant. The hypothesis was that the pediatric and adult IKDC questionnaires would show no clinically significant differences in score when completed by patients aged 13 to 17 years. Study Design: Cohort study (diagnosis); Level of evidence, 2. Methods: A total of 100 participants aged 13 to 17 years with knee injuries were split into 2 groups by use of simple randomization. One group answered the adult IKDC form first and then the pediatric form. The second group answered the pediatric IKDC form first and then the adult form. A 10-minute break was given between form administrations to prevent rote repetition of answers. Study design was based on established methods to compare 2 forms of patient-reported outcomes. A 5-point threshold for clinical significance was set below previously published minimum clinically important differences for the adult IKDC. Paired t tests were used to test both differences and equivalence between scores. By ordinary least-squares models, scores were modeled to predict adult scores given certain pediatric scores and vice versa. Results: Comparison between adult and pediatric IKDC scores showed a statistically significant difference of 1.5 points; however, the 95% CI (0.3-2.6) fell below the threshold of 5 points set for clinical significance. Further equivalence testing showed the 95% CI (0.5-2.4) between adult and pediatric scores being within the defined 5-point equivalence region. The scores were highly correlated, with a linear relationship (R2 = 92%). Conclusion: There was no clinically significant difference between the pediatric and adult IKDC form scores in adolescents aged 13 to 17 years. This result allows use of whichever form is most practical for long-term tracking of patients. A simple linear equation can convert one form into the other. If the adult questionnaire is used at this age, it can be consistently used during follow-up.