THE POSTERIOR TRIANGLE OF THE NECK

Using a simplified lateral view of the neck we can once again easily identify the Borders of the posterior triangle of the neck:

  • Sternocleidomastoid anteriorly
  • Trapezius posteriorly
  • Clavicle inferiorly

 

Roof of the posterior triangle: Platysma and superficial layer of the deep cervical fascia (Only platysma covers the vulnerable spinal accessory nerve crossing the posterior triangle)

Floor of the posterior triangle: A muscular floor and consists of the following muscles which are arranged, in order, from posterosuperior to anteroinferior:

1. Splenius capitis - ligamentum nuchae and upper thoracic spinous vertebrae to the mastoid process and occipital bone (draws head backward or to the respective side).

2. Levator scapulae - processes of C1-C4 to the superior aspect of the medial border of the scapula (elevates scapula).

3. Scalenus muscles

a. scalenus anterior - anterior tubercles of the transverse cervical processes to the scalene tubercle of the 1st rib.

b. scalenus medius - posterior tubercles of all of the transverse cervical processes to the first rib.

c. scalenus posterior - posterior tubercles of the transverse cervical processes to the 2nd rib.

All muscles of the posterior triangle, whether boundary or floor muscles, are enclosed by separate subdivisions of the deep investing fascia of the neck.

The posterior triangle of the neck can be further subdivided into:

BOUNDARIES OF THE OCCIPITAL TRIANGLE:

CONTENTS OF THE OCCIPITAL TRIANGLE:

  1. Spinal Accessory nerve (XI) - crosses the upper half of the triangle diagonally and, passing from the deep surface of sternocleidomastoid inferiorly on levator scapulae to reach the deep surface of trapezius, innervates sternocleidomastoid and trapezius.
  2. Superficial cervical cutaneous branches of Cervical plexus - formed from ventral primary rami of spinal nerves C2-C4, which emerge from posterior border of sternocleidomastoid
    1. Lesser Occipital (C2) – follows posterior border of SCM to innervate the scalp behind and above the ear.
    2. Great Auricular Nerve (C2,3) - crosses superficial to SCM and innervates the skin over the parotid gland, angle of the jaw and the posterior ear
    3. Transverse Cervical Cutaneous Nerve of the neck (C2,3) - crosses SCM superficially and, is cutaneous for the skin of the front and side of the neck (anterior triangle).
    4. Supraclavicular Nerves (C3,4) - divides into medial, intermediate, and lateral branches, which supply sensation over the shoulder(from the sternoclavicular joint to the acromion process), lateral neck and anterior upper thoracic wall.
  3. Part of the occipital and parts of the transverse cervical and suprascapular arteries are also found in the occipital triangle.

     

Some words about the Brachial Plexus and its relevance in the Occipital Triangle…..

The lower four cervical nerves (C5,C6,C7,C8) are found in the scalene gap (space between scalenus anterior and scalenus medius muscles) and they, along with the first thoracic nerve (T1), make up the brachial plexus. Cervical nerves C5, C6, join to form the superior (upper) trunk of the brachial plexus, and these nerves as well as part of the superior trunk are found in the occipital triangle. Branches from the roots of C5, C6, and C7, as well as from the superior trunk include:

  1. Dorsal scapular nerve - from the root of C5, pierces scalenus medius, and continues caudally on the deep surface of levator scapulae. This nerve innervates levator scapulae, rhomboids and it is accompanied by the dorsal scapular artery (deep branch of the transverse cervical artery).
  2. Long thoracic nerve - from the roots of C5, C6, C7. Once formed, it passes posterior to the brachial plexus and then along the chest wall (close to the mid-axillary line) to innervate serratus anterior.
  3. Superior trunk of the brachial plexus – Present in both triangles, this trunk will be discussed in detail in the next section

BOUNDARIES OF THE SUPRACLAVICULAR (Omoclavicular) TRIANGLE

CONTENTS OF THE SUPRACLAVICULAR (Omoclavicular) TRIANGLE

  1. Superior trunk of the brachial plexus - this trunk is formed by the union of C5 and C6 and two nerves come from this trunk. (Also present in Occipital Triangle)
  2. Suprascapular - through the suprascapular foramen to innervate supraspinatus and infraspinatus
    1. Suprascapular - through the suprascapular notch to innervate supraspinatus and infraspinatus

b. Nerve to subclavius - innervates subclavius

  1. Middle trunk of the brachial plexus - this trunk is the continuation of the anterior primary division of the 7th cervical nerve.
  2. Lower trunk of the brachial plexus - this trunk is formed from the anterior primary division of the 8th cervical and 1st thoracic nerves.
  3. Subclavian artery (3rd part) - the first part of the subclavian artery lies medial to scalenus anterior, the second part lies posterior to this muscle, and the third part lies lateral to the scalenus anterior. The thyrocervical trunk arises from the first part of the subclavian, and two of its several branches (transverse cervical, suprascapular), pass through both the supraclavicular and occipital triangles in route to their destinations. The transverse cervical supplies trapezius, subscapularis, levator scapulae and the rhomboids, while the suprascapular supplies supra and infraspinatus. Occasionally there are no branches from the third part of the subclavian. An exception is when the descending scapular (dorsal scapular) arises from the second or third part of the artery (deep part of the transverse cervical artery).
  4. External Jugular Vein: Derived from the Following Overview of venous drainage in the head and neck.
    1. Superficial Temporal and Maxillary veins unite to form Retromandibular vein.
    2. Retromandibular vein divides at angle of mandible into Anterior and Posterior divisions.
    3. Anterior division joins Facial Vein to form Common Facial vein which drains into Internal Jugular vein.
    4. Posterior division joins Posterior Auricular vein to form External Jugular vein.
    5. External Jugular vein descends across Sternocleidomastoid muscle to drain into Subclavian vein.
    6. Anterior Jugular vein forms from small veins below mandible;descends to join Ext. Jugular vein above clavicle. After lying superficial to the sternocleidomastoid muscle, the external jugular vein descends to the anterior angle of the posterior triangle where it enters the subclavian vein.

Region Anterior to Supraclavicular Triangle

An important landmark in this region is the scalenus anterior muscle which passes from the anterior tubercles of C3 - C6 to its attachment at the scalene tubercle on the first rib.

Using scalenous anterior as a landmark Subclavian Artery is divided into three main parts with several important branches:

First - lies medial to scalenus anterior

Second - lies posterior to scalenus anterior

Third - lies lateral to the lateral border of scalenous anterior as far as the outer border of the first rib