Ultrasound imaging of the serratus anterior muscle at rest and during contraction.

The purpose of this study is to describe a clinically feasible method for measuring the thickness of the serratus anterior (SA) muscle using rehabilitative ultrasound imaging ( RUSI) and to determine the reliability of repeated measures of that method. An exploratory clinical measurement study using a test-retest methodology was utilized to determine the reliability of the measurements in a sample of 20 healthy subjects. While sitting with the arm flexed 120°, the SA of each subject was imaged at rest, during an active hold and while holding a three pound weight. On Day 1, images were repeated three times for each condition by the same examiner. On Day 2, Examiner 1 and Examiner 2 repeated the scans. Images were examined offline by Examiner 1 with SA thickness measured superior to the most distal rib in the image. Reliability was evaluated using intraclass correlation coefficients ( ICCs) and Bland-Altman plots. The intra-examiner reliability (same day) during rest, active hold and active hold with resistance was ICC3,3 = 0·892; ICC3,3 = 0·951; and ICC3,3 = 0·869-0·971, respectively. Intra-examiner reliability between days ranged from ICC3,2 = 0·613 at rest to ICC3,2 = 0·736 during active hold with resistance. Interexaminer reliability was moderate during active hold (ICC2,2 = 0·526) and active hold with resistance (ICC2,2 = 0·535) and poor during rest (ICC2,2 = 0·425). This study demonstrates that SA thickness can be measured reliably using RUSI by the same examiner and suggests that active movements may increase that reliability. [ABSTRACT FROM AUTHOR]