The axillary arch (AA) has been thoroughly studied and described as a supernumerary muscle, present unilaterally or bilaterally. This study aims to provide an in vivo demonstration of the influence of an AA on vascular, biometrical, and hemodynamic parameters. Two-hundred thirty-nine subjects with a mean age of 21.3 ± 2.7 years participated in this study. After visual screening by two independent experts, 20 subjects (8.4%) presented with an AA unilaterally (n = 12) or bilaterally (n = 8). An echo-Doppler examination of the vena and arteria axillaris was performed to measure blood flow, velocity of circulating elements, and blood vessel diameter in different positions of the arm (abduction: 45°, 90°, 90° combined with exorotation 'ER', 120°). The arteria axillaris parameters, measured in the test (n = 9; six women, three men) and control group (n = 11; six women, five men), were equivalent for all tested positions. The axillary vein parameters, compared to variations within the groups, revealed no significant differences. However, when comparing variation between groups, significant differences were found for (i) diameter in 90° abduction + ER and 120° abduction; (ii) velocity in 90° and 120° abduction. Blood flow demonstrated no significant difference between groups in any of the positions. The results of this study indicate that there is no functional vascular implication of the AA in the test samples. This study also questions the interpretation of some hypotheses regarding the AA and entrapment syndromes.
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