Psychometric findings for LIMB-Q kids based on an international study of 800 children and adolescents with lower limb differences

Abstract

BACKGROUND: LIMB-Q Kids is a new patient-reported outcome measure (PROM) for children and adolescents with Lower limb differences (LLDs). This international field test study aimed to evaluate the psychometric properties of LIMB-Q Kids. METHODOLOGY: Patients from pediatric orthopaedic clinics with a diagnosis of LLDs were recruited. Participants completed LIMB-Q Kids and 2 generic quality of life questionnaires, i.e., PROMIS Pediatric Short Form v2.0 - Mobility 8a, and PedsQL. Demographic and clinical data were collected including the LLRS AIM Index, a measure of clinical severity for LLDs. Rasch measurement theory (RMT) analysis was used to examine the psychometric properties of LIMB-Q Kids. Test-retest (TRT) reliability was examined and tests of construct validity were performed. RESULTS: Participants (N = 800) were recruited from 16 sites in 7 countries. Participants were aged 8 years and older (mean = 13, standard deviation = 3.2, range 8-25 years) and had a broad range of LLDs (e.g., Leg Length Discrepancy, Fibular Hemimelia, Skeletal Dysplasia, Blount's disease, Posteromedial Tibial Bowing, Osteogenesis Imperfecta, Congenital Pseudarthrosis of Tibia, Tibial Hemimelia and Amputations). RMT analysis provided evidence of the reliability and validity of 9 independently functioning scales that measure leg appearance, physical function, symptoms (hip, leg, knee, ankle, and foot), leg-related distress, and social, and psychological function. In addition, TRT reliability based on a sample of 46 participants was high for all 9 scales (Intraclass correlation coefficient ranges from 0.76-0.95). LIMB-Q Kids Physical Function scale correlated strongly with the PROMIS Pediatric Short Form v2.0 - Mobility 8a (Pearson correlation 0.82) and the PedsQL Physical Function total score (Pearson correlation 0.77). As hypothesized, participants with more severe LLDs based on the LLRS AIM index scores reported lower scores on all LIMB-Q Kids scales, indicating more impact on the patients. CONCLUSIONS: This study provided evidence for the validity and reliability of LIMB-Q Kids. This new PROM can be used to inform research, quality improvement efforts, and clinical care. By measuring outcomes that matter most to children and adolescents with LLDs, LIMB-Q Kids can provide information to support evidence-based decisions. LEVEL OF EVIDENCE: Level III.