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KOOS-Child exhibits inadequate structural validity in a cohort of paediatric patients with ACL deficiency
  1. Christian Fugl Hansen1,
  2. Maria Østergaard Madsen1,
  3. Susan Warming2,
  4. Martin Wyman Rathcke1,
  5. Michael Krogsgaard1,
  6. Karl Bang Christensen3
  1. 1 Section of Sports Traumatology, Orthopedic Surgery Department, Bispebjerg and Frederiksberg Copenhagen University Hospital, Copenhagen, Denmark
  2. 2 Department of Physical and Occupational Therapy, Bispebjerg and Frederiksberg Copenhagen University Hospital, Copenhagen, Denmark
  3. 3 Department of Biostatistics, University of Copenhagen, Copenhagen, Denmark
  1. Correspondence to Dr Christian Fugl Hansen, Section for Sports Traumatology, Bispebjerg Hospital Orthopedic Surgery Department M, Copenhagen 2400, Denmark; christian.hansen{at}


Objectives Knee injury and Osteoarthritis Outcome Score (KOOS)-Child is a modification of the adult KOOS aiming to evaluate knee injury, including ACL deficiency. However, the measurement properties of KOOS-Child have not been assessed in a cohort of children with ACL deficiency. We aimed to study the structure of KOOS-Child using modern test theory models (Rasch analysis and confirmatory factor analysis (CFA)).

Methods Data were collected prospectively in a cohort of children with ACL deficiency at three time points: before-and-after ACL surgery, and at 1-year follow-up. For each subscale, structural validity through the fit of a CFA model was evaluated for 153 respondents. Modification indices were examined to find the model of best fit, confirmed using Rasch analysis. Responsiveness was reported for each subscale. Reliability was calculated for each item. Floor and ceiling effects, and Person-item distribution were reported.

Results All subscales showed inadequate fit to a unidimensional CFA model. Rasch analysis confirmed these results. Adjusting the subscales improved model fit, although this was still quite poor, except for the quality of life subscale. With one exception, all items demonstrated ceiling effects. Person-item distribution confirmed this. Due to lack of fit, reliability was not reported. All subscales were able to detect change from baseline to 1-year follow-up.

Conclusions KOOS-Child exhibits inadequate measurement properties in its current form for children with ACL deficiency. Suggestions to make the subscales fit the models better and improve accuracy of KOOS-Child are presented. However, the large ceiling effects observed may reduce sensitivity and induce type 2 errors.

  • Anterior Cruciate Ligament
  • Pediatrics
  • Statistics
  • Surveys and Questionnaires
  • Child Health

Data availability statement

Data are available on reasonable request.

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Data availability statement

Data are available on reasonable request.

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  • Contributors CFH (guarantor) and MK conceived and planned the project. CFH, MØM, MWR and SW collected data for the project, and KBC completed data analyses. All authors participated in writing the manuscript. CFH, MK and KBC directed the project.

  • Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.

  • Competing interests None declared.

  • Patient and public involvement Patients and/or the public were not involved in the design, or conduct, or reporting, or dissemination plans of this research.

  • Provenance and peer review Not commissioned; externally peer reviewed.

  • Supplemental material This content has been supplied by the author(s). It has not been vetted by BMJ Publishing Group Limited (BMJ) and may not have been peer-reviewed. Any opinions or recommendations discussed are solely those of the author(s) and are not endorsed by BMJ. BMJ disclaims all liability and responsibility arising from any reliance placed on the content. Where the content includes any translated material, BMJ does not warrant the accuracy and reliability of the translations (including but not limited to local regulations, clinical guidelines, terminology, drug names and drug dosages), and is not responsible for any error and/or omissions arising from translation and adaptation or otherwise.