Definition
- Compression of the brachial plexus, subclavian artery or vein
- Site between the neck root and axilla
- Neurogenic in the large majority, venous or arterial in the rest
Anatomy
- Interscalene triangle, anterior and middle scalene and first rib, containing plexus and artery
- Costoclavicular space between clavicle and first rib, where the vein is compressed
- Subcoracoid space deep to pectoralis minor
- Subclavian vein passes anterior to scalenus anterior
Aetiology
- Cervical rib or elongated C7 transverse process
- Roos fibrous bands and scalene anomalies
- Whiplash and clavicle malunion or nonunion with abundant callus
- Repetitive overhead activity, drooping shoulders and poor posture
Clinical Features
- Neurogenic TOS affects the lower trunk, C8 and T1
- Neck, shoulder and medial arm pain with ulnar paraesthesia, worse overhead
- Gilliatt-Sumner hand, thenar wasting more than hypothenar
- Venous TOS causes swelling, cyanosis and distended veins after exertion (Paget-Schroetter syndrome)
- Arterial TOS is rare, with cervical rib, pallor, claudication and digital emboli
- Adson, Wright hyperabduction and Roos tests have high false positive rates
Investigations
- Cervical spine and chest radiographs for cervical rib or apical lung lesion
- Nerve conduction shows reduced medial antebrachial cutaneous response and low median motor amplitude
- Dynamic duplex ultrasound
- CT or MR angiography and venography for vascular forms
- MRI brachial plexus and diagnostic scalene block
Differential Diagnosis
- C8 radiculopathy
- Cubital and carpal tunnel syndrome
- Pancoast tumour
- Shoulder pathology
- Motor neurone disease
Management
- Physiotherapy for posture, scapular stabilisation and scalene stretching
- Botulinum toxin to the scalenes in some centres
- Surgery for objective neurogenic TOS, failed nonoperative care and vascular TOS
- First rib resection with scalenectomy and excision of cervical rib or band
- Transaxillary, supraclavicular or infraclavicular approach
- Venous TOS, catheter-directed thrombolysis then first rib resection
- Arterial TOS, rib resection with arterial repair or bypass
Complications
- Pneumothorax
- Brachial plexus, long thoracic or phrenic nerve injury
- Subclavian vessel injury
- Left sided thoracic duct lymphatic leak
- Recurrence from scarring
Reviewed by Professor Phong Tran, Head of Orthopaedic Surgery, Western Health. Last updated 10 October 2026.