Concurrent Validity and Inter-Rater Reliability of the Motor Optimality Score-Revised in a Neonatal Surgical Population

<b>Objectives</b>: This study aims to evaluate the concurrent validity and inter-rater reliability and agreement of the Motor Optimality Score-Revised (MOS-R) in infants following major surgery in the neonatal period. <b>Methods</b>: A cross-sectional study of 211 term infants (mean GA 37.85 weeks, SD 2.10) with congenital anomalies requiring neonatal surgery assessed the concurrent validity of the MOS-R with the Bayley III and HINE at 3 months. Inter-rater reliability and agreement were determined using Gwet's Agreement Coefficient (AC₁), the intraclass correlation coefficient (ICC), and percentage agreement (%). <b>Results</b>: There were 209 infants assessed at 11-16 weeks post-term age (mean 13 weeks, SD 1.21), and a very weak correlation was observed between MOS-R and Bayley III for cognition (<i>p</i> = 0.02), expressive communication (<i>p</i> = 0.04), and gross motor (<i>p</i> < 0.001). When the MOS-R was categorised based on optimality, the only association was gross motor (<i>p</i> < 0.002). The MOS-R had a very weak correlation with the HINE total score (0.18, <i>p</i> < 0.001). The inter-rater reliability for the total MOS-R was substantial (AC₁ = 0.72). When the MOS-R was categorised as optimal, mildly reduced, moderately reduced, or severely reduced, we found good levels of agreement between raters (AC₁ = 0.76, 83% agreement). Perfect agreement (AC₁ = 1.00, 100%) was found for categorising the MOS-R using a predictive cut score for adverse outcomes (<23 vs. ≥23). <b>Conclusions</b>: At three months of age, the MOS-R showed weak associations with the HINE and Bayley III, indicating limited concurrent validity. Despite this, all tools offer valuable clinical insights. The inter-rater reliability for the MOS-R was good for categorising the MOS-R based on optimality and excellent when using a predictive cut-off score.