The Knee Injury and Osteoarthritis Outcome Score (KOOS) is distinguished from other knee-specific measures by the inclusion of separate scales for evaluation of activities of daily living, sports and recreation function, and knee-related quality of life, with presentation of separate subscale scores as a profile. However, its applicability in children has not been established. In this study, we examined how well the KOOS could be understood in a cohort of children with knee injury, with a view to preparing a pediatric version (KOOS-Child). A trained researcher conducted cognitive interviews with 34 Swedish children who had symptomatic knee injuries (either primary or repeated). They were 10-16 years of age, and were selected to allow for equal group representation of age and sex. All the interviews were recorded. 4 researchers analyzed the data and modified the original KOOS questionnaire. Many children (n =14) had difficulty in tracking items based on the time frame and an equivalent number of children had trouble in understanding several terms. Mapping errors resulted from misinterpretation of items and from design issues related to the item such as double-barreled format. Most children understood how to use the 5-point Likert response scale. Many children found the instructions confusing from both a lexical and a formatting point of view. Overall, most children found that several items were irrelevant. The original KOOS is not well understood by children. Modifications related to comprehension, mapping of responses, and jargon in the KOOS were made based on qualitative feedback from the children.

Background: The Knee injury and Osteoarthritis Outcome Score (KOOS) is a self-administered valid and reliable questionnaire for adults with joint injury or degenerative disease. Recent data indicate a lack of comprehensibility when this is used with children. Thus, a preliminary KOOS-Child was developed. This study aims to evaluate psychometric properties of the final KOOS-Child when used in children with knee disorders.Methods: 115 children (boys/girls 51/64, 7–16 years) with knee disorders were recruited. All children (n=115) completed the KOOS-Child, the Child-Health Assessment Questionnaire (CHAQ) and the EQ-5D-Youth version (EQ-5D-Y) at baseline to evaluate construct validity. Two additional administrations (1–3 weeks and 3 months) were performed for analyses of reliability (internal consistency and test–retest; n=72) and responsiveness (n=91). An anchor-based approach was used to evaluate responsiveness and interpretability.Results: After item reduction, the final KOOS-Child consists of 39 items divided into five subscales. No floor or ceiling effects (≤15%) were found. An exploratory factor analysis on subscale level demonstrated that items in all subscales except for Symptoms loaded on one factor (Eigenvalues 3.1–5.5, Symptom: 2 factors, Eigenvalue >1). Sufficient homogeneity was found for all subscales (Cronbach's α = 0.80–0.90) except for the Symptoms subscale (α = 0.59). Test–retest reliability was substantial to excellent for all subscales (Intraclass Correlation Coefficient 0.78–0.91, Smallest Detectable Change (SDC)_ind14.6–22.6, SDC_group1.7–2.7). Construct validity was confirmed, and greater effect sizes were seen in those reporting improved clinical status. Minimal important changes greater than the SDCs were found for patients reporting to be better and much better.Conclusions: The final KOOS-Child demonstrates good psychometric properties and supports the use of the KOOS-Child when evaluating children with knee disorders.

Purpose The current literature lacks sufficient information about improvements in gait patterns and function after total knee arthroplasty (TKA) and whether patients return to full function. This study evaluated change in gait, performance-based function, and self-reported function 1 year after TKA in patients with symptomatic knee osteoarthritis and how these aspects interrelate. Methods A total of 28 patients (64 % female) with knee osteoarthritis, with a mean age of 66 (±7) years, and 25 age- and gender-matched controls participated in this prospective cohort study. Three-dimensional gait analysis generated comprehensive measures of kinematic and kinetic gait deviations, respectively. Participants completed the Five Times Sit-to-Stand (5STS) test, and the self-reported questionnaire Knee Injury and Osteoarthritis Outcome Score (KOOS), at baseline prior to surgery and 1 year after TKA. Results Kinetic gait deviations of both the operated and non-operated limb persisted in patients with knee osteoarthritis at 1 year after surgery, while kinematic gait patterns were comparable to controls. Performance on the 5STS and KOOS scores in patients with knee osteoarthritis improved significantly 1 year after surgery (effect size 0.5–1.5), but did not reach the level of controls. Ten patients with knee osteoarthritis (36 %) exceeded the minimally detectable change on the 5STS. Conclusion Measures of overall gait patterns and the 5STS revealed improvements in function 1 year after TKA, but were not restored to the level of healthy controls. Based on change in 5STS performance, we identified patients with substantial improvements in gait patterns. Self-reported measures of function could not detect differences between patients improving in 5STS performance and those who did not. These findings highlight the use of the 5STS in clinical practice since improvement on this test seems to follow the reduction in gait pattern deviations. Level of evidence II.