Adson's sign

Adson's sign is seen during abduction and external rotation at the shoulder, where there is loss of the radial pulse in the arm. It can be a sign of thoracic outlet syndrome. Thoracic outlet obstruction may be caused by a number of abnormalities, including degenerative or bony disorders, trauma to the cervical spine, fibromuscular bands, vascular abnormalities, and spasm of the anterior scalene muscle. Symptoms are due to compression of the brachial plexus and subclavian vasculature, and consist of complaints ranging from diffuse arm pain to a sensation of arm fatigue, frequently aggravated by carrying anything in the ipsilateral hand or doing overhead work such as window cleaning.

As cited in the literature the Adson's sign is loss of radial pulse while turning the head to the contralateral side, slightly elevating the chin and breathing in.

How to perform Adson's Test?
With the patient in a sitting position, hands resting on thighs, the examiner palpates both radial pulses as The patient rapidly fills the lungs by deep inspiration and, with breath held, hyperextends the neck and turns the head toward the 'affected' side. If the radial pulse on that side is decidedly or completely obliterated, the result is considered positive.