IKDC or KOOS: which one captures symptoms and disabilities most important to patients who have undergone initial anterior cruciate ligament reconstruction?

Background: Knee-specific patient-reported outcome measures are frequently used after anterior cruciate ligament reconstruction but little is known about whether they measure outcomes important to patients.
Purpose: The aim of this study was to identify which instrument, the Knee injury and Osteoarthritis Outcome Score (KOOS) or the International Knee Documentation Committee Subjective Knee Form (IKDC), captures symptoms and disabilities most important to patients who have undergone initial anterior cruciate ligament reconstruction.
Study Design: Cross-sectional study; Level of evidence, 3.
Methods: Data were collected from 126 participants of an Internet knee forum. A self-reported online questionnaire was developed consisting of demographic and surgical data, the Tegner Activity Scale, and 49 consolidated items from the KOOS and the IKDC. Item importance, frequency, and frequency-importance product were calculated.
Results: Seventy-eight percent of the items from the IKDC were experienced by more than half of the patients, compared with 57% from the KOOS. Items extracted from the Function in Sports/Recreation and Quality of Life KOOS subscales were highly important to this group of patients. For patients 12 months or more after anterior cruciate ligament reconstruction, 94% of the IKDC items had a frequency-importance product of 1 or less compared with 86% of the KOOS items.
Conclusion: Overall, the IKDC items outperformed the KOOS items on all of the 5 criteria with the exception of the frequency-importance product for patients who were 12 months after anterior cruciate ligament reconstruction. The KOOS Function in Sports/Recreation and Knee-Related Quality of Life subscales outperformed the IKDC for the total cohort as well as for male and female subgroups. However, differences in individual items were not always evident from either total scale or subscale ratings. Studies should use patient-reported outcomes that reflect patients' most important concerns and further prospective longitudinal research is required in this area.