Establishing measurement properties in the assessment of inter-recti distance of the abdominal muscles in a postnatal women

Abstract

BackgroundDiastasis of the rectus abdominis muscle is often evaluated in clinical practice but it is unknown which clinical method has the best measurement properties. ObjectiveThe aim of this study was to determine: (i) the criterion validity of the callipers, tape measure and finger-width to evaluate the inter-recti distance of the abdominal muscles compared to ultrasound; and (ii) inter-rater and retest reliability of these methods. DesignMeasurement study. MethodsTwo physiotherapists assessed the inter-recti distance of rectus abdominis on 50 women postnatally using the three clinical methods. These measurements were compared to ultrasound and assessed for inter-rater and retest reliability. ResultsCallipers had very good positive correlations with ultrasound (r = 0.85 to 0.99) and narrow limits of agreement (LOA) (<6 mm). Finger-width and tape measure had moderate to very good correlation with ultrasound (tape measure r = 0.82 to 0.98; finger-width r = 0.75 to 0.98) with wider limits of agreement (tape measure LOA <8 mm; finger-width LOA <18 mm). Callipers demonstrated excellent inter-rater (ICC = 0.80 to 0.99) and retest (ICC = 1.00) reliability. Inter-rater reliability testing was very good for tape measure (ICC = 0.80 to 0.97) and moderate to very good (ICC = 0.44 to 0.85) for finger-width. Retest reliability demonstrated very good reliability (ICC = 0.99 to 1.00) for both finger-width and tape measure. The largest inter-recti distances, strongest correlations and reliability were found at the level of the lower umbilicus. ConclusionCallipers, tape measure and finger-width are valid and reliable methods of measuring inter-recti distance in postnatal women. Validity, and relative and absolute reliability were found to be the strongest using the callipers.