Initial psychometric evaluation of an upper extremity arthrogryposis multiplex congenita-specific measure using Rasch analysis.

BACKGROUND

In the absence of an upper extremity outcome measure specific to children with arthrogryposis multiplex congenita, a new outcome measure, the SHAPE-UP, was developed to help guide clinicians in their evaluation and decision making for treatment. It is designed for children with arthrogryposis multiplex congenita aged 1-21, consists of six descriptive questions and a video-recorded evaluation, divided into Task Completion and Analysis of Joint Motion and Position scales.

PURPOSE: The study aimed to evaluate the psychometric properties of the SHAPE-UP Task Completion scale using Rasch analysis and determine the correlation between the number of joints involved and the Task Completion score.

STUDY

DESIGN

This is a cross-sectional study including six participating Shriners hospitals.

METHODS

One hundred and one participants completed the SHAPE-UP, with 92 (54 female, mean age = 10.35 years, SD = 5.18 years) having upper limb involvement and included in the analysis. A Rash Analysis was used and the scoring was revised to improve fit.

RESULTS

The original SHAPE-UP included 11 tasks (46 items), scored on a five-point scale. Rasch analysis revealed a significant item-trait interaction (χ2 = 129.55; p < 0.05), with disordered thresholds in most items. Specialists revised the SHAPE-UP, collapsing the scoring options to three and removing four tasks, which improved the fit (χ2 = 29.9026; p = 0.968233). Content validity was adequate (-10 to 7 logits). Construct validity was achieved, and excellent reliability was established (0.96130). However, high local dependency was observed in multiple item sets. A correlation coefficient of r = -0.0466 (p < 0.05) was calculated.

CONCLUSIONS

The SHAPE-UP Task Completion scale aligns with Rasch model expectations. However, clinical interpretation of the Analysis of Joint Motion and Position scale is needed. Future studies should explore the reliability, validity, and responsiveness of SHAPE-UP.