The posterior triangle of the neck has the following boundaries and contents: 1) It is bounded by the middle third of the clavicle above, the investing layer of deep cervical fascia above, and the prevertebral fascia below. 2) It contains the upper trunk of the brachial plexus, apex of the lung, lymph nodes, subclavian artery and vein, external jugular vein, and spinal part of the accessory nerve. 3) A stab wound here could injure the upper trunk of the brachial plexus, cause bleeding from the subclavian artery or apex of the lung, and damage the 11th cranial nerve.

1. Posterior Triangle of Neck Dr. Skantha Kandiah MBA, MSc (NUI), MB BCh BAO (NUI), LRCP & SI Senior Lecturer in Anatomy and Lecturer in Healthcare Management RCSI

2. Posterior Triangle

3. Posterior Triangle Base: Middle 1/3 of the clavicle Roof: Investing layer of deep cervical fascia Floor: prevertebral fascia lying on splenius, levator scapulae and scalenus medius

4. Contents Upper trunk of Brachial Plexus Apex of the lung extends to 2cm above the middle 1/3 of the clavicle Lymph nodes Subclavian artery – at root of neck Subclavian vein – at root of neck External Jugular Vein Spinal part of XI

5. External Jugular Vein

6. XI Accessory nerve Spinal and Cranial parts Spinal part accessory nerve – superficial structure in posterior triangle 1/3 down the posterior border of SCM to 2/3 down the anterior border of trapezius

7. XI

8. XI SCM Trapezius How do you test above muscles? Spinal and cranial parts

9. Other Nerves…..

10. Cervical Plexus: Muscular Branches Anterior primary rami of the upper cervical nerves form the cervical plexus ansa cervicalis: C1,2,3 and XII (descendens hypoglossi) Ansa cervicalis supplies the strap muscles Phrenic nerve: C3,4,5

11. Cervical Plexus: Cutaneous Branches Lesser occipital C2: upper triangle, behind ear Great Auricular C2,3: skin over parotid Transverse Cervical C2,3: chin to sternum Supraclavicular C3,4

12. Stab Wound to Posterior Triangle Upper trunk brachial plexus injury What is it called? Apex of the lung is here, so what might happen? Bleeding from?

13. Sample Question Describe the boundaries and contents of the posterior triangle of the neck. Explain the consequences of a stab injury to the posterior triangle. Give surface markings of any important structures you name.