Longitudinal Invariance Testing Of The Knee Injury Osteoarthritis Outcome Score For Joint Replacement Scale (KOOS-JR).
Alexandra Dluzniewski, Caleb Allred, Madeline P Casanova and 3 others
PMID 37795315WHAT IT FOUND
The KOOS-JR is valid for comparing knee health between groups, but its stiffness item causes measurement bias over time.
Use the six-item version (KOOS-JR-6) to track patient recovery longitudinally. The full seven-item scale should not be used to measure change.
Key findings
01The seven-item KOOS-JR failed longitudinal invariance testing because the first item (stiffness) was interpreted differently by patients over time.
02Removing the stiffness item created a six-item version (KOOS-JR-6) that demonstrated sound longitudinal measurement invariance and detected significant improvement in knee health from baseline to 12 months.
03The original seven-item scale remained valid for comparing baseline scores across sex, age, and intervention groups.
STILL TO COME
How it was doneWhat they foundWhat it means for PTsWhat it means for OTs
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What it does not show
The study did not establish other key psychometric properties for the new six-item version, such as minimal clinically important differences (MCIDs) or responsiveness. The dataset lacked detailed demographic information (e.g., ethnicity, socioeconomic status, specific pathology severity), preventing invariance testing in these subgroups. The sample included very few patients under 41 years of age, so invariance was not tested in younger populations. The six-item version was derived from the existing data but has not yet been cross-validated in a new sample that only completed those six items.
Declared interests
The authors declare no competing interests. The work was supported by grants from the National Institutes of Health and the Idaho WWAMI Research Training Support Award.
The easy way to misread this
Do not assume the standard seven-item KOOS-JR is valid for tracking individual patient recovery over time. The study found that the morning stiffness item caused measurement bias longitudinally. Using the full scale to assess change may yield inaccurate results; use the six-item version (KOOS-JR-6) instead.