The term ‘thoracic outlet syndrome’ describes compression of the neurovascular structures as they exit through the thoracic outlet (cervicothoracobrachial region). The thoracic outlet is marked by the anterior scalene muscle anteriorly, the middle scalene posteriorly, and the first rib inferiorly.

Certain anatomical abnormalities can be potentially compromising to the thoracic outlet as well. These include the presence of a cervical rib, congenital soft tissue abnormalities, clavicular hypomobility, and functionally acquired anatomical changes. Soft tissue abnormalities may create compression or tension loading of the neurovascular structures found within the thoracic outlet (such as hypertrophy, a broader middle scalene attachment on the 1st rib or fibrous bands that increase the stiffness…). 

Congenital Factors:

• Cervical rib
• Prolonged transverse process
• Anomalous muscles
• Abnormalities of the insertion of the scalene muscles
• Fibrous muscular bands
• Exostosis of the first rib
• Cervicodorsal scoliosis
• Congenital uni- or bilateral elevated scapula
• Location of the A. or V. Subclavian in relation to the M. scalene anterior

Acquired Conditions:

• Postural factors
• Dropped shoulder condition
• Wrong work posture (standing or sitting without paying attention to the physiological curvature of the spine)
• Heavy mammaries
• Trauma
• Clavicle fracture
• Rib fracture
• Hyperextension neck injury, whiplash
• Repetitive stress injuries (repetitive injury most often from sitting at a keyboard for long hours)
  

Muscular Causes:

• Hypertrophy of the scalene muscles
• Decrease of the tonus of the M. trapezius, M. levator scapulae, M.rhomboids
• Shortening of the scalene muscles, M. trapezius, M. levator scapulae, pectoral muscles

Clinical symptoms

Signs and symptoms of thoracic outlet syndrome vary from patient to patient due to the location of the nerve and/or vessel involvement. Symptoms range from mild pain and sensory changes to limb-threatening complications in severe cases.

Patients with thoracic outlet syndrome will most likely present pain anywhere between the neck, face, and occipital region or into the chest, shoulder, and upper extremity and paresthesia in the upper extremity. The patient may also complain of altered or absent sensation, weakness, fatigue, and a feeling of heaviness in the arm and hand. The skin can also be blotchy or discoloured. A different temperature can also be observed.

Signs and symptoms are typically worse when the arm is abducted overhead and externally rotated with the head rotated to the same or the opposite side. As a result activities such as overhead throwing, serving a tennis ball, painting a ceiling, driving, or typing may exacerbate symptoms.