Extreme variability of vascular responses to slightly different abduction angles during abduction and external rotation tests, in patients with suspected thoracic outlet syndrome

<i>Objective.</i>Patients may not always perform a perfect 90° upper limb abduction when doing an abduction, external rotation test for the evaluation of thoracic outlet syndrome (TOS). We aimed to study the vascular responses to three slightly different abduction angles.<i>Approach.</i>We recorded fingertip arterial (A-PPG) and forearm venous (V-PPG) photo-plethysmography in 111 patients referred for suspicion or follow up of TOS. The measurements were made bilaterally during a 30 s surrender position, followed by moving elbows in the frontal plane without changing elbow and hand level to open the costo-clavicular angle (prayer position) to standardize venous results, either: slightly below (<90°), at the same level of (∼90°), or slightly above (>90°) the shoulder level, in a random order.<i>Main results.</i>With abnormal results defined as A-PPG <5%rest and V-PPG < 70%max in the surrender position, 54 of the 222 upper limbs were normal at all three tests. The proportion of abnormal tests decreased with the increase in abduction angle (Cochran<i>Q</i>< 0.05), 135 upper limbs showed impaired venous outflow for one (<i>n</i>= 74), two (<i>n</i>= 47) or the three angles (<i>n</i>= 14) without arterial inflow impairment at any of the three tests.<i>Significance.</i>Slight changes from a 'perfect' 90° abduction angle gave unreliable results during elevation, abduction, external rotation stress tests. A venous outflow impairment should probably be considered a physiologic response at <90° abduction.