Thoracic Outlet Syndrome

Thoracic Outlet Syndrome (TOS) is a medical condition given by compression of the brachial plexus and the subclavian vessels in their passage from the cervical and upper thoracic area toward the axilla and the proximal arm.

The brachial plexus is the nerve network that controls the muscles of the upper limb: it takes origin from 5 spinal nerves or roots. Once the nerve roots originate from the cervical spine, they pass between the anterior and the middle scalene muscles on both its side: then they run forming  an intricate nerve lace that passes underneath the clavicle, then heading toward the upper arm. The subclavian vessels (artery and vein) follow the coursTOSe of the nerves.

It is theoretically considered  that  compression on the neurovascular structures may occur at 3 levels:

  • between the anterior and middle scalene muscles
  • at their passage under the clavicle
  • under the insertion of the pectoralis minor muscle.

Yet it is practically admitted that symptoms related with TOS are generally originated by compression in the interscalenic space whereas the other two sites are seldom involved in its onset.


TOS related-symptoms may be resulting from:

  • anatomical anomalies of the bone structures or the muscles that may cause a static compression on the neurovascular structures during their course: in 10% of cases, TOS is associated with the so called “cervical rib” (supernumerary or extra rib, most frequently incomplete, arising at the level of the 7th cervical vertebra).
  • postural factors leading to the development of  hypertrophy of the scalene muscles. Such dynamic compression is certainly the cause  in the vast majority of cases.


Thoracic outlet syndrome is also known under other names that emphasize the etiology or the topography of the compression on the neurovascular structures:

  • Anterior scalene syndrome
  • Cervical rib syndromeTOS2
  • Costoclavicular syndrome

Symptoms of Thoracic Outlet Syndrome

Medical literature distinguishes 3 clinical forms of Thoracic Outlet Syndrome: arterial TOS, venous Tos and neurogenic TOS. The latter encompasses more than 90 % of overall TOS: therefore, being  the clinical presentation most frequently encountered, it is the one described here below.

Neurogenic TOS definitely  presents a much higher incidence in women in comparison with men. This might be explained as related also with constitutional factors: this entrapment syndrome seems to occur more frequently in slender women with long neck and narrow shoulders or in women with large breasts.

Symptoms of Thoracic Outlet Syndrome are:

  • Numbness along the ring and the little finger. Numbness along the thumb, index and middle finger can occur but it is definitely uncommon.
  • Numbness is constantly associated with pain on the shoulder and radiating along the upper arm, on the shoulder blade, the lateral wall of the chest and the homolateral
  • Numbness and pain are mostly occurring at night, often  becoming  so intense that patients can spend their nights  sleepless,  uselessly  trying to find relief.  Waking up in the morning, in many cases the hand is swollen, sometimes also presenting a different color if compared with the other one.
  • Intense pain and numbness can be elicited or increased after carrying weights (e.g. heavy shopping bags):  ladies even complain about being not able to carry their own bag on the affected shoulder as it constantly makes their symptoms worse.
  • Prolonged abduction (e.g. holding the phone with the affected arm for long conversations or the hairdryer) easily elicit or increase pain and numbness too. This explains why some working conditions predispose to the onset of this syndrome: professional musicians such as flautists and fiddlers, hairdressers, secretaries, carpenters, wall-painters are more prone to develop this syndrome in comparison with people doing other jobs, as they are obliged to work in non-ergonomic postures for long hours. Athletes of disciplines that require frequent and prolonged raising of the hands above the head (e.g. swimmers or volley-bally players) are also likely to develop symptoms related with TOS more frequently than in other sports.      TOS3

Occasionally the symptoms occur in young ladies, during their teenage years or in their early twenties. In such cases there is usually a different clinical presentation:

  • Pain and numbness are mild, inconstantly present or no present at all.
  • Weakness and progressive loss of interossei and thenar muscles may occur.


TOS can be cured. In mild cases, conservative treatment based on physiotherapy aimed to correction of non-TOS4ergonomic posture may be tried with benefit. Nevertheless if recurrence of symptoms occurs, surgery must be considered.

Surgery is the definitive solution and  consists in relieving the compression on the brachial plexus and the subclavian vessels: this is achieved performing a scalenectomy (that means cutting the insertion of the anterior scalene muscle) followed by external neurolysis (removing fibrous bands or scar tissue that may surround the neurovascular structures). Removal of cervical rib (if present) is only seldom needed as decompression and external neurolysis are enough in the vast majority of cases.   The procedure is always  carried under general anesthesia, accessing through a  transversal skin incision above the clavicle.

Postoperative immobilization is not required, postprocedural recovery is generally quick wih no limitation in the range of  movements of the upper limb, although the patient should avoid efforts during the first 3-4 weeks after surgery. Physical therapy aimed to correction of non-ergonomic posture is often advised after surgical treatment.


  • Surgery generally allows relief of pain and numbness
  • Long standing muscle atrophy often persists even after surgeryTOS5

Risk factors

It is well known that the onset of TOS can follow:

  • Traumas such as whiplash injuries
  • Repetitive strain


At the Neuro Spinal Hospital expert medical assessment and treatment are provided.

Diagnosing TOS may not be easy and straightforward for the majority of physicians as there are no specific investigations that reveal the syndrome; moreover its  clinical presentation often  mimics other pathologies (e.g. cervical herniated disk) or it can actually be associated  with other entrapment syndromes (e.g. association of TOS with Carpal Tunnel Syndrome or entrapment of the ulnar nerve at the elbow) in a quite relevant number of cases. Therefore the syndrome is suspected and assessed only on clinical evaluation, this requiring great experience and knowledge of the pathology.

Our staff is also able to offer the physical therapy that is often required in such cases.

Once it is diagnosed and correctly treated  Thoracic Outlet  Syndrome offers a good prognosis, with relief of symptoms.