Any MRIs? Or x rays?
Those check for extra cervical ribs or any other anomalies like larger bones than usual.
Vascular doppler test?
Doppler Ultrasound Test: Why It'''s Done, Risks, What to Expect

With an abnormal shoulder position/injury I might consider looking for a very good chiropractor or body worker.. Read reviews and ask around to find the really good ones..

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