1. POSTERIOR TRIANGLE
OF NECK
STEVEN J. ZEHREN, PH.D.

2. BOUNDARIES
OF POSTERIOR TRIANGLE

3. 1. The POST. TRIANGLE IS BOUNDED BY the sternocleidomastoid (SCM) anteriorly, the trapezius posteriorly and the middle third of the clavicle inferiorly.
2. The apex of the triangle is superior and the base inferior (formed by clavicle).

4. STERNOCLEIDOMASTOID MUSCLE (SCM)
Mastoid process
Origin: Sternal head --- manubrium
Clavicular head --- medial 1/3 of clavicle
Insertion: Mastoid process and lateral ½ of superior nuchal line
Sternal head
Clavicular head

5. Functions: Unilaterally: tilts head toward shoulder on same side (lateral flexion); rotates head so face turns to opposite side.

6. Functions (bilaterally): Flexion of CV when person is supine
Functions (bilaterally): Flexion of CV when person is supine. If head and neck fixed, SCM can elevate sternum and clavicle (forced
Inspiration).

7. TORTICOLLIS
1. Torticollis (L. tortus, twisted + L. collum, neck) is a contraction of the cervical muscles that produces twisting of the neck and slanting of the
head. Occasionally the SCM is injured when an infant’s head is pulled too much during a difficult birth, tearing its fibers. This results in
fibrosis and shortening of the SCM. Surgical release of the SCM from its inferior attachments to the manubrium and clavicle may be
necessary to enable the person to hold and rotate the head normally. (Moore and Dalley, COA, 5th ed., p. 1055).

8. TRAPEZIUS MUSCLE
Origin: Superior nuchal line, ext. occipital protuberance, lig. nuchae, spines of C7 – T12
Insertion: Lateral 1/3 of clavicle, acromion, spine of scapula
Functions: elevation of scapula (sup. fibers), depression of scapula (inf. fibers), retraction of scapula (middle fibers), superior rotation of glenoid fossa of scapula (sup. + inferior fibers).

9. XI. SPINAL ACCESSORY N.
SKELETAL MOTOR --- TO STERNOCLEIDOMASTOID & TRAPEZIUS MUSCLES XI
STERNOCLEIDOMASTOID M.
TRAPEZIUS M.
1. In addition to an innervation by XI, the SCM & trapezius are innervated by the ventral rami of cervical nn. (2-4) (more later).

10. ROOF
OF POSTERIOR TRIANGLE

11. Investing layer of deep cervical fascia Platysma m.
1. The ROOF of the post. triangle is the platysma m. and the investing layer of cervical fascia.
2. The platysma is a muscle of facial expression and will be discussed later.
Platysma m.

12. FLOOR
OF POSTERIOR TRIANGLE

13. MUSCLES OF FLOOR OF POSTERIOR TRIANGLE
Splenius capitis m.
Levator scapulae m.
Post., mid., & ant.
scalene mm.
The FLOOR of the post. triangle is the splenius capitis, levator scapulae, and the posterior, middle, and anterior scalene muscles.

14. FASCIAL FLOOR OF POSTERIOR TRIANGLE
Prevertebral layer
of deep cervical fascia
The muscles of the floor are covered with the prevertebral layer of deep cervical fascia (more later).

15. SPLENIUS CAPITIS MUSCLE
Origin: Lower ½ of lig. nuchae, spines of C7 – T4.
Insertion: Mastoid pr., skull below lateral 1/3 of sup. nuchal line
Innervation: Dorsal rami of cervical nn.
Functions: Bilaterally: Extend head
Unilaterally: Rotate head to same side

16. LEVATOR SCAPULAE MUSCLE
Origin: Transverse prs. C1 – C4.
Insertion: Upper part of medial border of scapula
Function: Elevates scapula

17. INNERVATION OF LEVATOR SCAPULAE M.
In addition to innervation by dorsal scapular n., the levator is innervated by the ventral rami of C3-C4

18. SCALENE MUSCLES Anterior scalene m. Middle scalene m.
Posterior scalene m.
1. Discuss O and I or scalene mm.
a. Ant. scalene m.
O – ant. tubercles of transverse processes of C3 – C6
I - scalene tubercle and ridge of rib 1
b. Middle scalene m.
O - post. tubercles of transverse processes of C2 – C7
I - broad attachment to upper surface of rib 1
c. Posterior scalene m. (only incompletely separated from the middle scalene m.)
O – post. tubercles of transverse processes of C5 – C7
I - lateral surface of rib 2
Rib 1

19. MUSCLES PRODUCING MOVEMENT OF THE CERVICAL INTERVERTEBRAL JOINTS
1. Bilateral action of longus colli and scalene mm., as well as SCM, produce flexion of neck.
Bilateral action of the scalene mm. can also elevate ribs 1-2 (inspiration)
2. Unilateral action of intertransverse and scalene mm. (as well as other mm. not shown) produce lateral flexion of neck.

20. INNERVATION OF PREVETEBRAL AND SCALENE MUSCLES
VENTRAL RAMI:
1. Prevertebral and scalene mm. innervated by ventral rami of cervical nerves.

21. CONTENTS
OF POSTERIOR TRIANGLE

22. OMOHYOID MUSCLE

23. OMOHYOID MUSCLE Omohyoid (superior belly) Omohyoid m. (inferior belly)
1. Only the inferior belly of omohyoid m. lies in the posterior triangle; superior belly in anterior triangle.
2. Will discuss this muscle in connection w/ the other infrahyoid mm. (anterior triangle lecture).
Omohyoid m. (inferior belly)

24. OCCIPITAL AND OMOCLAVICULAR TRIANGLES
Occipital triangle
1. Note that inferior belly of omohyoid subdivides posterior triangle into 2 other triangles.
Omoclavicular triangle
(supraclavicular triangle)
(subclavian triangle)

25. NERVES

26. CAREFREE & CAREFUL ZONES
XI runs posteroinferiorly across the post. triangle and divides it into an upper "CAREFREE ZONE" and a lower "CAREFUL ZONE". This is because superior to XI one can dissect without care (there are not many structures in this area) but inferior to XI great caution must be exercised !

27. CAREFREE & CAREFUL ZONES
Accessory N. (XI)
1. Only some cutaneous nerves and occipital a. (not shown) in CAREFREE ZONE.
2. Point out brachial plexus, 3rd part of subclavian artery, etc. in the CAREFUL ZONE.

28. Sternocleidomastoid m.
F. magnum
Jugular f.
C2 spinal n.
Acessory n. (XI)
Sternocleidomastoid m.
C3 spinal n.
C4 spinal n.
Trapezius m.
1. XI originates from neurons in spinal cord segments Cl-C5. The axons of these neurons leave the cord, join together and ascend as a single nerve through the f. magnum. XI then exits the skull through the jugular f. and passes posteroinferiorly. It supplies only two muscles --- the SCM and trapezius.
2. Note that C2,C3, and C4 spinal nerves also send branches into the SCM and TRAP. According to Netter, these are both efferent (supplementing XI) and afferent (proprioceptive). Books may differ on the function of the cervical nerve innervation of these muscle.
3. Also, we will consider efferent fibers in XI as SVE, although other books may differ on this point.
Efferent fibers
Afferent fibers

29. “Roger Travis Drinks Cold Beer”
5 Roots
(vental rami)
3 Trunks
3 ant. Divisions
3 post. Divisions C5 C6
Superior
3 Cords C7
Middle C8
5 terminal Branches
Inferior T1
Lateral
Musculocutaneous n.
Posterior
The BRACHIAL PLEXUS innervates the upper limb. It has several parts --- Roots, Trunks, Divisions, Cords and Branches (terminal) (Mnemonic: " Roger Travis Drinks Cold Beer"). The roots and trunks are supraclavicular in position and lie within the post. triangle . The "roots" of the plexus are formed by the VENTRAL RAMI of C5-T1. The ventral rami of C5 & C6 join to form the sup. trunk, the ventral ramus of C7 continues as the middle trunk and the ventral rami of C8 & T1 join to form the inf. trunk. Each trunk divides into an anterior and a posterior division. The posterior divisions of all three trunks unite to form the posterior cord; the anterior divisions of the superior and midde trunks unite to form the
lateral cord; the anterior division of the inferior trunk continues as the medial cord. The five terminal branches arise from the various cords as shown here.
Axillary n.
Medial
Radial n.
Median n.
“Roger Travis Drinks Cold Beer”
Ulnar n.

30. BRACHIAL PLEXUS IN RELATIONSHIP TO CLAVICLE
1. Note that roots and trunks are supraclavicular, divisions postclavicular, and cords and terminal branches infraclavicular in position.
2. For anesthesia of upper limb, the anesthetic agent is injected superior to the midpoint of the clavicle.

31. FIVE COMPONENTS OF CERVICAL PLEXUS: XII XI
Cutaneous
NerveS C1
Motor Nerves
To Prevertebral
Muscles
Ansa Cervicalis: C2
SUPERIOR ROOT C3
INFERIOR ROOT
Contributions
From C3 & C4
To XI C4
1. Cervical plexus is the ventral rami of C1 – C4.
2. Orient viewer, pointing out XI and XII.
3. There are 5 parts to the cervical plexus, some of which I have already mentioned. (motor nerves to prevertebral and scalene mm.,
contributions to XI).
4. I will now discuss the cutaneous branches of the plexus.
ANSA
Phrenic Nerve

32. CUTANEOUS BRANCHES OF THE CERVICAL PLEXUS
A number of CUTANEOUS NERVES (BRANCHES OF THE CERVICAL PLEXUS) appear at the post. border of the SCM and radiate in different directions. These include the supraclavicular nn. (to skin of upper chest and shoulder), transverse cervical n. (to skin of ant. triangle), great auricular n. (to skin of ear and parotid region) and lesser occipital n. (to skin of ear and scalp). All of these nerves contain fibers from C2 & C3 except the supraclavicular nn. (C3&C4).
Regional anesthesia of the skin of the neck can be accomplished by a CERVICAL PLEXUS BLOCK. The main site of injection is just superior to the midpoint of the post. border of the SCM. This is known as the NERVE POINT OF THE NECK. (ERB’S POINT).
Lesser occipital n. (C2,3)
Great auricular n.(C2,3)
Transverse cervical n. (C2,3)
Supraclavicular nn. (C3,4)

33. VESSELS

34. ARTERIES IN POSTERIOR TRIANGLE
1. The SUBCLAVIAN A. has 3 PARTS based on its relationship to the ant. scalene m.
2. Only the 3rd part lies in the posterior triangle; after crossing the first rib it becomes the axillary a. (to the upper limb).
3. The transverse cervical a. and the suprascapular a. are also contents of the posterior triangle. They arise from the thyrocervical trunk (1st pt.
of subclavian a.) and course across the anterior scalene m. 1 3

35. ARTERIES IN POSTERIOR TRIANGLE
TRANSVERSE CERVICAL A.
THYROCERVICAL TRUNK
SUPRASCAPULAR A.
1. Transverse cervical and suprascapular aa. distribute to scapular region.

36. EXTERNAL JUGUAR VEIN Subclavian v. Superficial temporal v.
Maxillary v.
Facial v.
Posterior auricular v.
Retromandibular v.
Common facial v.
(to IJV)
External jugular v.
Transverse cervical v.
1. Discuss formation, course and termination of EJV. Also note its tributaries in the inferior part of posterior triangle.
2. Prominence of EJV. The EJV may serve as an “internal barometer”. When venous pressure is in the normal range, the EJV is
usually visible above the clavicle for only a short distance. However, when venous pressure rises (e.g., heart failure), the EJV is
prominent throughout its course. Thus, observation of EJV during physical exam may give diagnostic sign of heart failure, SVC
obstruction, enlarged supraclavicular lymph nodes, or increased intrathoracic pressure.
3. Severance of EJV. If the EJV is severed where it pierces the roof of the posterior triangle, its lumen is held open by the investing layer of deep
cervical fascia, and the negative intrathoracic pressure will suck air into the vein. A venous air embolism produced in this way will fill the right
side of he heart w/ froth, which nearly stops blood flow through it, resulting in dyspnea and cyanosis. The application of firm pressure to the
severed EJV until it can be sutured will prevent this.
Suprascapular v.
Anterior jugular v.
Subclavian v.

37. INTERSCALENE TRIANGLE

38. BOUNDARIES & CONTENTS OF THE INTERSCALENE TRIANGLE
Anterior scalene m.
Middle scalene m.
1. Note the posterior relationships of the anterior scalene m. and define the borders of the interscalene triangle. Discuss clinical significance of interscalene triangle. (see next two slides).
Brachial plexus
Subclavian a.
Rib 1

39. Anterior scalene m. Middle scalene m. Cervical rib compresses
subclavian a.
1. The interscalene triangle may become too narrow due to the presence of a CERVICAL RIB. A cervical rib can compress the subclavian a. leading to ischemia (reduced blood supply) to the upper limb.
2. Cervical ribs ( % occurrence) (RTW).

40. Lowest trunk of brachial plexus elevated by cervical rib
A CERVICAL RIB can also compress the brachial plexus. Note how the lowest TRUNK of the plexus is elevated with consequent compression of the nerve fibers leading to pain, paresthesia and muscular weakness. Compression of the subclavian a. and/or brachial plexus in the interscalene triangle is termed ANT. SCALENE SYNDROME.

41. ANTERIOR RELATIONSHIPS OF ANTERIOR SCALENE MUSCLE
Ascending cervical a.
Anterior scalene m.
Phrenic n.
Inferior thyroid a.
Transverse cervical a.
1. Note that anterior scalene m. is the KEY muscle in the root of the neck with regard to important relationships.
Point out the anterior relationships of this muscle.
2. Note that phrenic nerve can be blocked with anesthetic or surgically crushed on anterior surface of ant. scalene m. to achieve paralysis of
hemidiaphragm (see COA, 5th ed., p.1064 for details).
Suprascapular a.
Thyrocervical trunk
Subclavian v.

42. SUBCLAVIAN VEIN PUNCTURE
1. The subclavian vein is often the point of entry to the venous system (for central line placement). Central lines are inserted to administer
nutritional fluids and medications, and to measure central venous pressure.
2. In an infraclavicular subclavian v. approach , the thumb of one hand is placed on the middle part of the clavicle and the index finger in the
jugular notch. The needle punctures the skin inferior to the thumb and is advanced medially toward the tip of the index finger until the tip
enters the right venous angle, posterior to the sternoclavicular joint.
3. If the needle is not inserted carefully, it may puncture the pleura and lung, resulting in a pneumothorax. It may also puncture the subclavian a.
(see next slide).
4. If possible, right subcalvian vein puncture is desirable in order to avoid damage to the thoracic duct.

43. CERVICAL PLEURA (CUPULA)
1. If the needle is not inserted carefully, it may puncture the pleura and lung, resulting in a pneumothorax. It may also puncture the subclavian a.
Cervical pleura

44. DEEP FASCIAE OF NECK

45. Retropharyngeal space
Investing fascia
Retropharyngeal space
Pretracheal fascia *
Buccopharyngeal fascia *
Carotid sheath
Common carotid a.
Internal jugular v.
Vagus n.
The DEEP CERVICAL FASCIA is arranged in three layers. The INVESTING LAYER (red) is the most superficial. It forms a "tubular sleeve" or "investment" around the neck. It splits to enclose the SCM and trapezius; between these muscles it is a single layer that contributes to the roof of the post. triangle. The PREVERTEBRAL LAYER (orange) covers the prevertebral muscles (eg, longus colli) but it is more extensive than its name suggests. It continues laterally and posteriorly to cover the scalene and levator scapulae mm., thus contributing to the floor of the post. triangle. The VISCERAL LAYER of cervical fascia has two components --- PRETRACHEAL (blue) and BUCCOPHARYNGEAL (green). Together, these two components form a tubular sleeve around the cervical viscera (trachea, esophagus, thyroid gland). The pretracheal fascia forms a sheath for the thyroid gland. The buccopharyngeal fascia connects the two lobes of the thyroid gland; it also covers the post. surface of the esophagus.
The CAROTID SHEATH is another fascial structure in the neck. It is a tubular sheath enclosing the common (or internal) carotid a. (medially), the internal jugular v. (laterally) and the vagus n. (posteriorly). Just outside the sheath is the sympathetic trunk.
The RETROPHARYNGEAL SPACE is the most important fascial space in the neck. Its boundaries are as follows: buccopharyngeal fascia (ignore the alar fascia) (anterior), prevertebral fascia (posterior) and carotid sheath (lateral). This space is CLINICALLY IMPORTANT BECAUSE IT PROVIDES A ROUTE FOR THE SPREAD OF INFECTION. Infectious material (eg, from an abscessed tooth) can enter the space and pass inferiorly into the chest.
Note the ANTERIOR SCALENE M. and the nerves related to it. The phrenic n. is directly anteior. Directly posterior is a structure labelled "spinal nerve". Can you be more specific in its identification? (Hint: What nervous structure lies between the ant. and middle scalene mm.?)
Prevertebral fascia
* = Component of visceral fascia

46. Buccopharyngeal fascia
Base of skull
Buccopharyngeal fascia
Retropharyngeal space
Prevertebral fascia
1. The VERTICAL EXTENT OF THE RETROPHARYNGEAL SPACE is from the base of the skull to the posterior mediastinum (area of chest post. to heart and pericardium).
2. Retropharyngeal space filled w/loose areolar tissue to allow pharynx and esophagus to expand when swallowing.
Mediastinum