Intra-rater and inter-rater reliability of rehabilitative ultrasound imaging(RUSI) for assessing muscle thickness in upper extremity muscles in healthy adults

Background: Rehabilitative ultrasound imaging (RUSI)-based measurement is increasingly used for quantitative assessment of skeletal muscle morphology in clinical and rehabilitation settings.However, evidence regarding the reliability of upperextremity muscle thickness measurements is limited.Design: Cross-sectional study Objective: : To investigate the intra-rater and inter-rater reliabilities of RUSI for measuring the thickness of the extensor carpi radialis longus (ECRL) and the flexor carpi ulnaris (FCU) in healthy adults.Methods: : Twenty-three healthy adults participated in this cross-sectional repeated-measures study.Two experienced physical therapists independently measured the thicknesses of the ECRL and FCU using RUSI under standardized conditions.Intra-rater(3,1), and inter-rater reliability were assessed using correlation analysis (2,1).Standard error of measurement (SEM), minimal detectable change (MDC), and Bland-Altman plots were additionally used to evaluate measurement agreement.Results: Intra-rater reliability was excellent for both muscles, with correlation coefficients ranging from 0.94 to 0.98.Inter-rater ICC point estimates ranged from 0.85 to 0.90, indicating good-to-excellent reliability, although the confidence interval for FCU inter-rater reliability was relatively wide.SEM values ranged from 0.30 to 0.83 mm, and MDC values ranged from 0.83 to 2.30 mm.Bland-Altman plots showed that most measurements were distributed within the 95% limits of agreement, indicating acceptable agreement between repeated measurements and raters.Inter-rater measurements had wider limits of agreement than intra-rater measurements, particularly for the FCU.Conclusions: RUSI showed that for measuring upper-extremity muscle thickness in healthy adults, intra-rater reliability was excellent, and while FCU inter-rater reliability was relatively wide, inter-rater reliability ranged from good to excellent.These findings support the potential clinical applicabilityof RUSI for the quantitative assessment of forearm muscle morphology, although examiner consistency and standardized measurement protocols remain important to minimize measurement variability.