Ultrasonographic Measurement of the Thickness of Axillary Recess Capsule in Healthy Volunteers

OBJECTIVE To evaluate the inter-rater and intra-rater reliability of ultrasonographic measurements of axillary recess (AR) thickness in healthy individuals, and to analyze the factors affecting the thickness of the AR capsule. METHODS We recruited 20 healthy individuals (10 male, 10 female) with a mean age of 37 years (standard deviation ±10). Two physiatrists (an experienced and a novice rater) independently investigated the AR thickness in three rounds. The AR thickness was measured for each individual at three shoulder abduction angles (50°, 70°, and 90°). Intra-class correlation (ICC) coefficients were used to assess the reproducibility of each measurement. RESULTS Excellent intra-rater reliability coefficients were observed at the three shoulder abduction angles, in the analysis of both raters. The inter-rater reliability coefficient was also was excellent in both studies. There were significant differences in the AR thickness, according to the angle of shoulder abduction. The AR was thicker at 50° than at 70° and 90° (all p<0.001), and the AR was thicker at 70° than at 90° (p<0.001). Height (r=0.62, p=0.003) and body mass index (r=0.52, p=0.019) were positively correlated with AR thickness. Males had a thicker AR capsule than females at all three angles (all p<0.001). CONCLUSION Ultrasonographic measurements of AR thickness in healthy individuals demonstrate excellent intra-rater and inter-rater reliability. AR thickness may depend on anthropometric variables and position of the shoulder.