Psychometric properties of functional mobility outcome measures in children with arthrogryposis multiplex congenita.

The study was cross-sectional, so it cannot tell us how sensitive these measures are to change over time or how well they track progress in response to intervention. MIDs were calculated using only statistical methods because patient-reported 'change' data was not available. These are initial benchmarks and may not fully reflect what patients consider a meaningful improvement. Agreement between measures was assessed using the median score of this specific sample as a cut-off, which may not be applicable to other populations. The PROMIS Pediatric self-report had approximately 40% missing data because it was only given to children aged 8 and older, which may affect the reliability of those specific findings.

The authors declared no conflicts of interest. The study was funded by the Islamic Development Bank, Shriners Hospitals for Children, Fonds de Recherche du Québec - Santé, Centre for Interdisciplinary Research in Rehabilitation, Faculty of Medicine at McGill University, and the American Society for Bone and Mineral Research.

Do not assume that a small numerical improvement on one scale means the child's mobility has meaningfully changed. The study found that these four measures often disagree on a child's mobility level, and the Minimal Important Difference is a statistical estimate from a cross-sectional sample, not a proven clinical threshold for tracking progress over time.