What Is Thoracic Outlet Syndrome?

Thoracic outlet syndrome (TOS) refers to a spectrum of conditions arising from compression of the neurovascular structures — the brachial plexus, subclavian artery, and subclavian vein — as they pass through the thoracic outlet: the triangular space bordered by the anterior scalene muscle anteriorly, the middle scalene posteriorly, and the first rib inferiorly. Three subtypes are recognised based on the primary structure compressed: neurogenic TOS (by far the most common, accounting for over 90% of cases) involves brachial plexus compression, producing arm and hand symptoms; venous TOS involves subclavian vein compression, producing arm swelling and venous engorgement; and arterial TOS — the rarest but most serious — involves subclavian arterial compression, producing ischaemic symptoms in the hand. Neurogenic TOS, while common, is frequently misdiagnosed or missed entirely because its symptom pattern overlaps substantially with cervical radiculopathy, carpal tunnel syndrome, and shoulder pathology.

Causes and Predisposing Factors

The thoracic outlet has limited space. Several factors reduce this space further and compress its contents. Structural anomalies — a cervical rib (an accessory rib arising from C7), elongated C7 transverse process, or fibromuscular bands — are present in 10–15% of the population and significantly narrow the costoclavicular space. Scalene muscle hypertrophy or spasm — common in overhead workers, swimmers, and after whiplash injury — compresses the neurovascular bundle between the anterior and middle scalenes. Postural dysfunction — forward head posture with protracted, anteriorly tilted scapulae and elevated first ribs — reduces the thoracic outlet dimensions during sustained arm positions. Repetitive overhead activities in occupational and sporting contexts load the thoracic outlet repeatedly. Trauma — particularly motor vehicle accidents with cervical injury — can initiate scalene fibrosis and scarring that chronically compresses the brachial plexus.

Recognising Neurogenic TOS

Neurogenic TOS produces a characteristic but variable symptom complex. The most common complaint is aching pain and paraesthesiae (tingling, numbness) in the arm, hand, and often the neck and shoulder, following the distribution of the lower brachial plexus (C8–T1) — the medial forearm, ring finger, and little finger. Symptoms are consistently provoked by sustained overhead arm positions, carrying heavy bags, and prolonged arm use in front of the body. Night symptoms are common. Weakness in the intrinsic hand muscles may accompany advanced cases. The EAST test (elevated arm stress test) — sustained arm abduction at 90 degrees and external rotation with repetitive hand opening for three minutes — reliably reproduces symptoms in neurogenic TOS. Adson's test (pulse change with neck rotation and extension) is less sensitive but more specific for arterial involvement.

Overlap with other conditions: TOS commonly coexists with cervical radiculopathy, carpal tunnel syndrome, and cubital tunnel syndrome — a phenomenon called double crush syndrome, where proximal neural compression sensitises the nerve to secondary compression distally. Assessment must evaluate the entire neural pathway from the cervical spine to the hand.

Conservative Treatment

Conservative management is appropriate for neurogenic TOS and resolves symptoms in the majority of patients when diligently applied. Treatment targets the structures creating the compression. Scalene manual therapy — myofascial release, trigger point treatment, and dry needling to the anterior and middle scalenes — directly reduces the muscular compression on the brachial plexus. First rib mobilisation — reducing first rib elevation, which narrows the costoclavicular space — is a key manual intervention. Postural rehabilitation addresses forward head position, scapular protraction, and thoracic kyphosis; exercises for the deep cervical flexors, serratus anterior, and lower trapezius are central. Neural mobilisation — median, ulnar, and brachial plexus sliders — improves neural tissue mobility and reduces neural hypersensitivity. Ergonomic modification of workstation setup and activity patterns reduces provocative loading. Surgery — first rib resection and scalenectomy — is reserved for refractory cases or vascular TOS.

References & Further Reading

  1. Sanders RJ, Hammond SL, Rao NM. Diagnosis of thoracic outlet syndrome. J Vasc Surg. 2007;46(3):601–604.
  2. Hooper TL, et al. Thoracic outlet syndrome: a controversial clinical condition. J Man Manip Ther. 2010;18(2):74–83.
  3. Likes K, et al. Prospective evaluation of prevalence of TOS. J Vasc Surg. 2014;59(3):709–712.