Thoracic outlet syndrome affects the shoulder, arm, hand or all three locations. Symptomsare caused by compression of the nerves in the brachial plexus (nerves that pass into the arms from the neck) or blood vessels. The hand pain is usually most severe in the fourth and fifth fingers. The pain is aggravated by the use of the arm, and “fatigue” of the arm is often prominent. Causes or thoracic outlet syndrome include trauma to the head or neck area, a fracture of the first rib or clavicle, poor posture, or subluxation of the cervical vertebrae.