CN XI runs superficially in the posterior triangle, making it vulnerable to injury
Causes: Surgical procedures in the posterior triangle (lymph node biopsy, radical neck dissection), penetrating trauma
Result: Paralysis of trapezius → drooping of shoulder, winging of scapula (medial rotation of inferior angle of scapula), weakness of abduction of arm beyond 90°
Also paralysis of SCM → weakness of head rotation to opposite side
Cervical Lymphadenopathy
Supraclavicular lymph nodes in the posterior triangle drain the thoracic and abdominal viscera via lymphatics that travel with the thoracic duct
Left supraclavicular node (Virchow’s node): Palpable in advanced malignancies of stomach, colon, lung, breast — called Troisier’s sign
Cervical lymphadenopathy in the posterior triangle is also seen in: tuberculosis, lymphoma, metastatic carcinoma, infectious mononucleosis
Brachial Plexus
Brachial plexus block: Can be performed in the posterior triangle via the interscalene approach (between scalenus anterior and medius) — used for upper limb surgery
Brachial plexus injury: Trunks are vulnerable in the supraclavicular triangle during violent downward traction of the shoulder (e.g., motorcycle accidents)
Upper trunk (Erb’s palsy): C5, C6 — waiter’s tip position
Lower trunk (Klumpke’s palsy): C8, T1 — claw hand
Cervical Rib / Thoracic Outlet Syndrome
A cervical rib (arising from C7 vertebra) may elevate the lower trunk of brachial plexus and compress the subclavian artery in the posterior triangle
Results in: Tingling/numbness in medial forearm and hand (C8, T1 distribution), diminished radial pulse, Raynaud’s phenomenon
This is a form of thoracic outlet syndrome
External Jugular Vein
Visible on surface when raised intrathoracic pressure (Valsalva) or elevated JVP
Can be used for emergency venous access
Distension at 45° head elevation = raised JVP (normal = not distended above clavicle)
Subclavian Artery
Subclavian steal syndrome: Stenosis of subclavian artery proximal to vertebral artery origin → retrograde flow in vertebral artery → symptoms of vertebrobasilar insufficiency on exercise of ipsilateral arm
Aneurysm of subclavian artery (3rd part) may produce a pulsatile swelling in the supraclavicular fossa
