Posterior triangle of the neck

Boundaries

It has the following boundaries:

Apex: Union of the sternocleidomastoid and the trapezius muscles at the superior nuchal line of the occipital bone

Anterior: Posterior border of the sternocleidomastoideus

Posterior: Anterior border of the trapezius

Base: Middle one third of the clavicle

Roof: Investing layer of the deep cervical fascia

Divisions

The posterior triangle is crossed, about 2.5 cm above the clavicle, by the inferior belly of the omohyoid muscle, which divides the space into two triangles:

an upper or occipital triangle

a lower or subclavian triangle (or supraclavicular triangle)

Contents

A) Nerves and Plexuses:

Spinal accessory nerve (Cranial Nerve XI)

Branches of cervical plexus

Roots and trunks of brachial plexus

Phrenic nerve (C3,4,5)

B) Vessels:

Subclavian artery (Third part)

Transverse cervical artery

Suprascapular artery

Terminal part of external jugular vein

C) Lymph Nodes:

Occipital

Supraclavicular

D) Muscles:

Inferior belly of omohyoid muscle

Anterior Scalene

Middle Scalene

Posterior Scalene

Levator Scapulae Muscle

Splenius

Clinical significance

The accessory nerve (CN XI) is particularly vulnerable to damage during lymph node biopsy. Damage results in an inability to shrug the shoulders or raise the arm above the head (e.g., for brushing hair), particularly due to compromised trapezius muscle innervation.

The external jugular vein's superficial location within the posterior triangle also makes it vulnerable to injury. It is also the site of clinical examination of Jugular venous pressure.

The right atrial pressure is reflected in it because there are no valve in the entire course of this vein and is straight, therefore used to examine Jugular Venous Pressure.

As external jugular vein pierces the fascia, the margins of the vein get adherent to fascia. So if the vein gets cut, it cannot close and air is sucked in due to negative intrathoracic pressure causes air embolism. To prevent this, fascia colli has to be cut.