Adson's sign is the loss of the radial pulse in the arm by rotating head to the ipsilateral side with extended neck following deep inspiration.
Limitations, and pathophysiology of thoracic outlet syndrome 
Adson's sign is no longer used as a positive diagnosis of TOS since many people without TOS will show a positive Adson's.
There is minimal evidence of interexaminer reliability.
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 ipsilateral 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 (feels) 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.
See also