Download Posterior Triangle of the Neck HO

Posterior Triangle of the Neck
By
Prof. Dr. Muhammad Imran Qureshi
For the purpose of anatomical description the neck is sub divided into two major
triangles, the ‘Anterior’ and the ‘Posterior’ by muscle bellies and bones.
The Sternocleidomastoid muscle separates the posterior triangle from the anterior.
Each of these is further divided into sub triangles.
The Posterior triangle: There is one triangle on
each side of the neck and each is bounded by:
The Sternocleidomastoid
The Trapezius and
The middle third of the Clavicle.
The Posterior triangle is divided by the Inferior belly
of the Omohyoid muscle into:
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The Occipital triangle (bounded by the
Sternocleidomastoid, Trapezius and Inferior belly of Omohyoid muscle)
The Subclavian / Supraclavicular / Omoclavicular triangle (bounded by the
Sternocleidomastoid, middle third of the Clavicle and the Inferior belly of
Omohyoid).
The Occipital triangle is larger than the Subclavian triangle
The Anterior triangle: There is one triangle on each side of the neck and each is
bounded by:
The Sternocleidomastoid
The Inferior border of the Mandible, and
The Midline of the Neck.
It is further subdivided into:
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The Digastric triangle, bounded by the anterior and posterior bellies of the
Digastric muscle and the inferior border of the Mandible.
The Submental triangle, bounded by the two anterior bellies of the Digastric
muscles and the body of the Hyoid bone.
The Carotid triangle bounded by the Sternocleidomastoid, the Posterior belly
of the Digastric muscle, and the Superior belly of the Omohyoid muscle, and
The Muscular triangle, which is bounded by the Sternocleidomastoid,
Superior belly of the Omohyoid and the Midline of the Neck.
The Posterior Triangle
Boundaries:
Anterior: Posterior border of
Sternocleidomastoid muscle
Posterior: Anterior border of Trapezius
muscle
Inferior (Base): Middle third of the Clavicle
Roof: Investing layer of deep Cervical fascia.
It encircles the neck, covers the posterior
triangle, splits to envelop the
Sternocleidomastoid and Trapezius and
attaches to the clavicle. In the lower part,
Platysma also forms part of the roof
Floor: the floor is formed (from above
downwards) by the Splenius capitis, Levator
scapulae, Scalenus anterior, Scalenus
Medius and Scalenus posterior muscles.
These muscles are covered by the
Prevertebral fascia
CONTENTS OF THE POSTERIOR TRIANGLE:
Cutaneous Nerves and Spinal part of
Accessory Nerve
The External Jugular Vein
Brachial Plexus (Roots and Trunks)
Inferior belly of Omohyoid muscle
Lymph nodes
Subclavian artery and vein,
Suprascapular and transverse cervical
arteries, Dorsal scapular artery and
Occipital artery
STRUCTURES DEEP TO THE
STERNOCLEIDOMASTOID:
The Carotid Sheath
The Internal Jugular Vein
THE CAROTID ARTERIES
Sternocleidomastoid & Trapezius: These split
from one sheet of embryonic muscle. Above,
these two muscles have a continuous
attachment extending from the mastoid process (behind the ear) to the inion (in the
midline). Since this attachment is aponeurotic, it produces a ridge, the Superior Nuchal
line. These two muscles separate as they descend below. Therefore, they have
discontinuous attachment on the clavicle.
A part of the sternocleidomastoid crosses the
sternoclavicular joint.
Spinal Part of the Accessory nerve: It is the
nerve to sternocleidomastoid and Trapezius
muscles and spans the gap between the two. Here
it is quite superficial
It divides the triangle into nearly two equal parts:
The upper part is carefree part for there is
no important structure to damage but below
one must be very careful
As it emerges from the jugular foramen
(Accompanied with other nerves and vessels) it
passes obliquely downwards and backwards
from the transverse process of the atlas to
the superior angle of the scapula. Along its
course it burrows through the
sternocleidomastoid a short distance below
the mastoid process. Here lymph nodes
surround it. It crosses the posterior triangle
and disappears under cover of the trapezius,
just above the clavicle. Sensory twigs from
C2, C3 and C4 join it.
Injury to this nerve in the posterior triangle
results in a dropping of the shoulder
downward and forward .
In the posterior triangle there is an area about
the size of a coin whose center is at the
midpoint of the posterior border of the
sternocleidomastoid muscle. From here, the
cutaneous nerves of the cervical plexus
radiate. All of them leave the triangle in various
directions. The lesser occipital (from cervical
segment C2) parallels the posterior border of
the sternocleidomastoid muscle after hooking
around the 11th nerve and ascends to the
occipital region; The great auricular (C2 and
C3) crosses the sternocleidomastoid
obliquely toward the lobe of the ear; The
anterior / transverse cutaneous (C2 and C3)
leaves the triangle by crossing the sternocleidomastoid muscle transversely to reach the
skin of the anterior triangle. The medial, intermediate, and lateral supraclavicular nerves
stem from a trunk formed by anterior rami of C3 and C4 and supply the skin over the
lower part of the posterior triangle. In addition, the medial and intermediate
supraclaviculars cross the clavicle to supply the skin of the upper pectoral region. The
lateral supraclavicular crosses the anterior
border of the trapezius muscle superficial
to the angle of the trapezius and clavicle to
supply the skin over the shoulder tip.
Inferior belly of Omohyoid Muscle: It
passes about an inch above the clavicle to
which it is bound by an inverted sling of
fascia. It subdivides the posterior triangle
into a smaller lower subclavian triangle and
a larger upper occipital triangle.
External Jugular vein: This large vein
descends subcutaneously across the
sternocleidomastoid and pierces the deep
fascia to end in the subclavian vein. Its tributaries in
the posterior triangle are the transverse cervical,
suprascapular, and anterior jugular veins. The last
communicate with each other.
The Floor: The fibres of the muscles of the floor run
obliquely downward and backward.
Levator scapulae occupies a middle position. It lies
deep to the accessory nerve and runs parallel to it.
Above it lies the Splenius Capitis. Below it are the
three Scalene muscles. Above the Splenius Capitis a
small part of Semispinalis capitis can sometimes be
seen.
The muscular floor of the triangle is carpeted with a layer of fascia (The prevertebral
fascia). This carpet covers the subclavian vessels and the roots of the brachial plexus
and thus provides them with a covering (the Axillary sheath) as they enter the axilla. It
also covers and guards the motor nerves to four important muscles (Levator scapulae,
Rhomboids, Serratus anterior and Diaphragm)
Lymph Nodes: They are embedded in the fat between the
fascial roof and the fascial floor and form the lateral group of
Inferior deep cervical (Supraclavicular) lymph nodes.
They drain the back of the scalp and neck. Usually they receive
some efferent vessels from the upper deep cervical, axillary and
deltopectoral nodes. These nodes empty into the subclavian
lymph trunk. The axillary nodes empty into the subclavian lymph
trunk, which follows the subclavian vein to the thoracic or right
lymph duct. They Get enlarged in Infections of the Scalp and
Rubella.
Subclavian Artery: Its only branch given off in the
posterior triangle is the dorsal scapular artery. The
branches from the subclavian artery usually come
from the second part (behind scalenus anterior) and
first part (proximal to that muscle).
Other Arteries in the Posterior Triangle: The
Suprascapular and Transverse cervical arteries,
which arise from the first part of the artery via
thyrocervical trunk. They pass laterally in front of the
scalenus anterior and its fascia and the phrenic
nerve. Across the apex of the triangle one can have
the glimpse of the occipital artery
Brachial Plexus: Roots are located behind the
Scalenus anterior muscle. Trunks are located in the
lower part of the triangle. The roots receive gray
rami from the middle and inferior cervical ganglia
and first and second thoracic ganglia.
Cutaneous Nerves: C1 has no cutaneous branch.
The ventral rami of C5 to T1 form the brachial
plexus. Thus C2, C3 and C4 supply the cutaneous
territory between the Trigeminal nerve above and T 2
below. They do this by means of FOUR nerves that
radiate from about the middle of the posterior border
of sternocleidomastoid
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The Lesser Occipital Nerve (C2, C3): It
hooks around the accessory nerve and
ascends just behind and parallel to the
posterior border of the
sternocleidomastoid to supply the
scalp.
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The Greater Auricular Nerve (C2,
C3): It runs vertically across the
sternocleidomastoid to the lobe of the
ear, with the external jugular vein. It
has mastoid, auricular and facial
branches
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The Anterior Cutaneous Nerve of the
Neck / Transverse Cervical nerve
(C2,C3): It crosses the
sternocleidomastoid and the external
jugular vein and supplies the skin between the jaw and the sternum
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The Supraclavicular Nerves (C3, C4): These
are three sensory branches to the lower part of
the posterior triangle and upper chest wall
down to the level of the second rib.