1. The Brachial Plexus – anatomy, lesions and neurophysiology studies
Jim Lewis, R.NCS.T., CNCT

2. Nerves that originate above or very high in the brachial plexus
Spinal Accessory (CN XI)
Phrenic (C3-C5)
Dorsal Scapular (C5)
Suprascapular (C5-C6)
Long Thoracic (C5-C7)

3. Brachial Plexus
The brachial plexus is an arrangement of nerve fibers (a plexus) running from the spine (vertebrae C5-T1), through the neck, the axilla (armpit region), and into the arm.
There are 5 groups of nerve fiber interconnections, roots, trunks, divisions, cords, and branches (or nerves).

4. Trunks
The 5 roots of the brachial plexus lie deep to below the sternocleidomastiod muscle.
These roots unite to form the trunks.
The upper trunk is formed by the C5 and C6 nerve roots.
The middle trunk has just one nerve root, C7. The so- called axis of symmetry.
The lower trunk is formed by the C8 and T1 roots.

5. Divisions The trunks divide into The anterior division and
The posterior division
These generally indicate if their nerve fibers serve the front (anterior division) or back (posterior division) of the limb.

6. Cords
The divisions pass deep to the clavicle and enter the axilla, where they give rise to three large nerve bundles
The Cords
lateral, medial and posterior
All along the brachial plexus small nerves branch off.

7. Branches or Nerves
The brachial plexus ends within the axilla where the three cords separate into the 5 important nerves of the upper limb;
musculocutaneous,
axillary,
radial,
median and
ulnar

9. The DeMyer Method The 5-3-3-5 method Simple Quick
Draw it right in the procedure room while performing the NCS
Covers 80% of what we need

10. 5 3 3 5
Roots
Trunks
Cords
Branches/Nerves C5
1. Write 5 – 3 – 3 – 5 across the top of the page and label as shown C6
2. Write C5 – T1 across the
left side of the page C7
C7 – Middle Trunk – Posterior cord = axis of symmetry C8 T1
3. Draw an arrow head connecting C5 and C6, then do the same for C8 and T1.
Draw straight lines from the tip of these two arrowheads and from C7, across the page, as shown

11. 5 3 3 5
Roots
Trunks
Cords
Branches/Nerves
4. Label these three trunks
Upper, Middle and Lower as shown C5
Upper C6
5. Draw an arrow head connecting the upper and lower trunks to the middle, as shown.
Middle C7 C8
Lower T1

12. 5 3 3 5
Roots
Trunks
Cords
Branches/Nerves C5
Upper
Lateral
6. Label these three cords Lateral, Posterior and Medial as shown C6
Middle
Posterior C7 C8
Lower
Medial T1
7. Draw an arrow head connecting between the posterior and the medial cord (median nerve). Extend the end as shown.

13. 5 3 3 5
Roots
Trunks
Cords
Branches/Nerves C5
Upper
Lateral C6
Middle
Posterior C7 C8
Lower
Medial
8. Draw a connector (median nerve fibers) from the Middle trunk to the lateral cord, as shown T1
9. Draw an connector off the posterior cord (axillary nerve) , as shown

14. 5 3 3 5
Roots
Trunks
Cords
Branches/Nerves C5
Upper
Lateral
Musculocutaneous C6
Axillary
Radial
Middle
Posterior C7
Median C8
Lower
Medial
Ulnar T1
10. Label the 5 nerves, as shown

15. The Upper Trunk The upper trunk is formed by the C5-C6 nerve roots.
The upper trunk divides:
The anterior division proceeds to the lateral cord
The posterior division proceeds to the posterior cord

16. The Anterior Division of the Upper trunk
The anterior division proceeds to the lateral cord and finally, the
Outer branch of the median nerve
Both motor and sensory fibers. The motor fibers innervate the pronator teres and flexor carpi radialis (with fibers from C7, middle trunk) while the sensory fibers continue to the lateral portion of the hand, and
Musculocutaneous nerve
Both motor and sensory fibers. Motor fibers innervate the biceps, coracobrachialis, and brachialis muscles. The sensory branch, called the lateral antebrachial cutaneous nerve supplies the skin over the lateral aspect of the forearm

17. The Posterior Division of the Upper trunk
The posterior division proceeds to the posterior cord and branches to the:
Axillary nerve
Both motor and sensory fibers. Motor fibers innervate the deltoid muscle while sensory fibers innervate sensation over the deltoid region, and
Radial nerve
Both motor and sensory fibers. Motor fibers innervate the brachioradialis and extensor carpi radialis (longus and brevis) with some contributions to the triceps and supinator. Sensory fibers continue to the lateral dorsum of the hand.
Also exiting high in the upper trunk is the suprascapular nerve
A motor nerve innervating the supraspinatus and infraspinatus muscles in the scapular region.

18. The Middle Trunk The middle trunk is formed entirely from the C7 root.
Sometimes called the “Axis of Symmetry,” because C7 runs directly into its cord while C5-C6 unites into the upper trunk and C8-T1 unites into the lower trunk.
The posterior division goes directly to the posterior cord
The anterior division carrying median sensory fibers proceeds to the lateral cord

19. The Posterior Division of the Middle trunk
The posterior division goes directly to the posterior cord which,
Becomes the axillary nerve (although all fibers supplying the axillary nerve come from the upper trunk),
Radial nerve,
Motor fibers innervate most of the triceps, and portions of the extensor digitorum communis and extensor indicis proprius as well as the rest of the extensor muscles in the forearm. The muscles in the forearm are innervated after the radial nerve splits and the motor branch becomes the posterior interosseous nerve.
Thoracodorsal nerve, innervating a portion of the latissimus dorsi and
Subscapular nerve which innervates a portion of the teres major.

20. The Anterior Division of the Middle trunk
The anterior division proceeds to the lateral cord
Outer branch of the median nerve
Innervating sensory fibers to the middle finger.
In NCS this is a very important point.
When evaluating for brachial plexopathies, not recording from the middle finger means you miss middle trunk fibers.
Remember the radial SNC is upper trunk.

21. The Lower Trunk The lower trunk is formed by the C8-T1 nerve roots.
The anterior division continues to the medial cord
The posterior division of the lower trunk proceeds to the posterior cord

22. The Anterior Division of the Lower trunk
The anterior division continues to the medial cord and finally, the
Ulnar nerve
Both motor and sensory fibers. The motor fibers innervate the flexor carpi ulnaris in the forearm and the abductor digiti minimi, first dorsal interosseous and the deep head of the flexor pollicis brevis muscles in the hand. Sensory fibers innervate the fourth and fifth digit of the hand.
Inner branch of the median nerve
Motor fibers to the abductor pollicis brevis, the superficial head of the flexor pollicis brevis and the opponens pollicis

23. The Posterior Division of the Lower trunk
The posterior division of the lower trunk proceeds to the posterior cord
Radial nerve
Innervates the additional portions of the radial/posterior interosseous muscles not supplied from C7 and middle trunk

24. Medial Antebrachial Cutaneous nerve
Additionally, the medial antebrachial cutaneous branches from the medial cord and innervates sensation to the medial forearm.

25. 5 3 3 5
Roots
Trunks
Cords
Branches/Nerves C5
Upper
Lateral
Musculocutaneous
LABC C6
Axillary
Radial
Middle
Posterior C7
Median C8
Ulnar
Lower
Medial T1
MABC

26. Lesions of the Brachial Plexus
Injuries and diseases can affect the plexus and cause damage.
Upper trunk plexopathies can be caused by a birth trauma, radiation therapy, and neuralgic amyotrophy.
Middle trunk plexopathy is rare and usually caused by injury.
Lower trunk plexopathy is usually caused by trauma, a Pancoast tumor, Dejerine-Klumpke, CABG (associated with a jugular vein), and metastatic disease.

27. Lesions of the Brachial Plexus
Traumatic injuries are the most common cause of brachial plexus lesions.
automobile,
motorcycle,
bicycle accidents,
penetrating knife, or
gunshot wounds.
Most Traumatic plexopathies are the result of traction and stretch injuries.
Severe traction injuries may result in damage to the roots as well as the plexus.

28. Lesions of the Brachial Plexus
Root avulsions are when the nerve roots are torn and axons are damaged beyond repair.
They often occur in combination with brachial plexus injuries.
The most common roots affected in root avulsions are C8/T1.

29. Lesions of the Brachial Plexus
Nontraumatic plexopathies include neuralgic amyotrophy (sometimes called Parsonage-Turner syndrome or idiopathic brachial plexopathy),
hereditary brachial plexopathy,
neoplastic or radiation induced brachial plexopathy and
neurogenic thoracic outlet syndrome to mention a few.

30. Some needle stuff Panplexus: Complete Brachial plexopathy.
Muscles Affected:
all except the
serratus anterior and
rhomboids
these are innervated by nerves (long thoracic and dorsal scapular, respectively) that come directly off the roots, proximal to the plexus.

31. Upper trunk plexopathies
These are the most common brachial plexopathies.
Weakness occurs in nearly all muscles with C5-6 innervation including the deltoid, biceps brachii, brachioradialis, supraspinatus and infraspinatus (the patient has difficulty lifting their arms).
Muscles with partial upper trunk contribution such as pronator teres (C6/7) and triceps(C6/7/8) may be affected
Sensory loss occurs in the lateral arm, lateral forearm, lateral hand, and thumb.

32. DTR’s
Biceps and brachioradialis reflex depressed
Triceps preserved

33. Nerve Conduction Studies
Exclude a C5/6 radiculopathy or other mononeuropathies
Sensory Nerve Conductions
Abnormal
Median (thumb and index finger), radial and lateral antebrachial cutaneous sensory nerves will show reduced amplitudes particularly when compared to the unaffected arm.
Normal
The median (to the middle and ring finger), ulnar and medial antebrachial cutaneous nerves would be normal
If the patient has a C5/6 radiculopathy or a root avulison the sensory nerves would be unaffected

34. Nerve Conduction Studies
Motor nerve conduction studies
Abnormal
Musculocutaneous and axillary motor nerve studies would show decreased CMAP amplitude as compared to the unaffected side.
Normal
Routine motor nerve conduction studies of the median and ulnar nerves are not particularly useful in distinguishing upper trunk or C5- 6 radiculopathies, but MNC’s would be absent in avulsion injuries to C5-6.
Of note, you could spare the patient the musculocutaneous nerve as you have already performed the LABC sensory, an extension of that nerve.

35. Some needle stuff
Upper trunk plexopathy: Upper trunk lesion (C5-C6 roots).
Muscles Affected:
Deltoid,
biceps,
brachioradialis,
supraspinatus, and
infraspinatus .
Of note: the lesion could be distal to the suprascapular nerve which would spare the supraspinatus and infraspinatus.
Muscles partially affected are the
pronator teres (C6-7) and
triceps (C6-C7-C8).

36. 5 3 3 5
Roots
Trunks
Cords
Branches/Nerves C5
Upper
Lateral
Musculocutaneous
LABC C6
Axillary
Radial
Middle
Posterior C7
Median C8
Ulnar
Lower
Medial T1
MABC

37. Middle trunk plexopathies
Isolated middle trunk plexopathies are rare.
Signs and symptoms resemble those of a C7 radiculopathy.
Weakness occurs in the elbow, wrist and finger extensors.
Sensory loss occurs in the posterior forearm and the dorsal and palmar aspect of the middle finger.
Only triceps DTR abnormal

38. Nerve Conduction Studies
Sensory nerve conduction studies
Abnormal
Median sensory response to the middle and ring finger will be reduced as compared to the unaffected side.
While median sensory fibers to the thumb and index finger transverse the upper trunk the sensory fibers to the middle finger originate in the C7 nerve root and go through the middle trunk and anterior division before joining the rest of the median sensory fibers in the lateral cord.
Normal
The remaining sensory nerve conduction studies should be unaffected

39. Nerve Conduction Studies
Motor nerve conduction studies
Abnormal
Radial motor conduction study may show reduced amplitude (has lower trunk innervation as well)
Normal
The remaining motor nerves of the upper limb will be spared
It can be difficult to distinguish a lesion involving the middle trunk from one involving the posterior cord as there are no nerve branches arising directly from the middle trunk.

40. Some needle stuff
Middle Trunk Plexopathy: Middle trunk is formed from C7 root.
Muscles Affected:
Triceps,
flexor carpi radialis, and
pronator teres muscles.
Middle trunk lesions mimic C7 radiculopathies, so needle examination of the cervical paraspinals is necessary.

41. 5 3 3 5
Roots
Trunks
Cords
Branches/Nerves C5
Upper
Lateral
Musculocutaneous
LABC C6
Axillary
Radial
Middle
Posterior C7
Median C8
Ulnar
Lower
Medial T1
MABC

42. Lower trunk plexopathies
Lower trunk plexopathies present with symptoms similar to C8-T1 radiculopathies, medial cord plexopathies and even ulnar neuropathies.
Weakness is evident in all median and ulnar innervated hand muscles as well as radial innervated distal forearm and wrist muscles.
The involvements of radial C8 muscles (lower trunk, posterior cord) help localize the lesion to the lower trunk by excluding the medial cord.
Sensory disturbance is seen in the medial aspect of the arm, forearm and hand in a larger distribution than an ulnar neuropathy.
No DTR changes

43. Nerve Conduction Studies
Sensory nerve conduction studies
Abnormal
Ulnar and medial antebrachial cutaneous nerves reveal reduced amplitudes especially when compared to the unaffected side.
Normal
Median sensory nerves remain unaffected
Motor nerve conduction studies
There would be decreased CMAP amplitude in both ulnar and median motor NCS, although this might be true in severe a severe C8-T1 radiculopathy as well. Distal radial response to the EIP may be decreased (has middle trunk innervation as well).
Remaining motor nerves are unaffected.

44. Some needle stuff
Lower Trunk Plexopathy: Lower trunk is formed from C8-T1 nerve.
Muscles Affected:
All ulnar nerve innervated muscles (flexor carpi ulnaris, flexor digitorum profundis, lumbrical muscles, opponens digiti minimi, flexor digiti minimi, abductor digiti minimi, interossei, adductor pollicis), in addition to
median C8-T1 muscles (abductor pollicis brevis, flexor pollicis longus, flexor digitorum profundus), and
radial C8 innervated muscles (extensor indicis proprius and extensor pollicis brevis).

45. 5 3 3 5
Roots
Trunks
Cords
Branches/Nerves C5
Upper
Lateral
Musculocutaneous
LABC C6
Axillary
Radial
Middle
Posterior C7
Median C8
Ulnar
Lower
Medial T1
MABC

46. Lateral cord plexopathies
Weakness of shoulder flexion and abduction, elbow, arm pronation and wrist flexion.
Sensory loss can be found in lateral forearm, lateral hand, and first three fingers.
Biceps DTR’s are abnormal, triceps and brachioradialis spared

47. Nerve Conduction Studies
Sensory nerve conduction studies
Abnormal
Median innervated first three digits and the lateral antebrachial cutaneous innervated lateral forearm should show reduced amplitude as compared to the unaffected side.
Normal
The radial innervated thumb would be preserved in lateral cord lesions (posterior cord), but would be involved if the lesion were in the upper trunk

48. Nerve Conduction Studies
Motor nerve conduction studies
Abnormal
Musculocutaneous nerve to the biceps would show reduced amplitude as compared to the unaffected side.
Normal
Median and ulnar nerves originate from C8-T1, lower trunk and medial cord thus would be unaffected in lateral cord lesions.
Study of the axillary nerve should be preserved in lateral cord lesions as it originated in the upper trunk, but transverses the posterior division and continues through the posterior cord.

49. Some needle stuff
Lateral cord Plexopathy: Musculocutaneous nerve and C6-C7 portions of the median nerve.
Muscles Affected:
Pronator teres,
flexor carpi radialis, and
biceps.

50. 5 3 3 5
Roots
Trunks
Cords
Branches/Nerves C5
Upper
Lateral
Musculocutaneous
LABC C6
Axillary
Radial
Middle
Posterior C7
Median C8
Ulnar
Lower
Medial T1
MABC

51. Posterior cord plexopathies
Poserior cord plexopathies, like middle trunk plexopathies, are uncommon.
The radial, axillary, upper and lower subscapular and thoracodorsal nerves are derived from the posterior cord.
Symptoms of posterior cord lesions include weakness of shoulder abduction and adduction, wrist drop and finger drop, and arm extension weakness.
Sensory loss is evident in the lateral arm, posterior arm, forearm, and radial dorsal hand.
Triceps and brachioradialis reflexes abnormal

52. Nerve Conduction Studies
Sensory nerve conduction studies
Abnormal
The superficial radial nerve (upper trunk, posterior cord) would show low amplitude especially compared to the unaffected side.
Normal
The lateral antebrachial cutaneous (upper trunk, lateral cord), median (upper and middle trunks, lateral cord), ulnar and medial antebrachial cutaneous (lower trunk, medial cord) nerves should be normal.

53. Nerve Conduction Studies
Motor nerve conduction studies
Abnormal
Motor study to the radial innervated extensor indicis proprius would be expected to show reduced amplitude.
The axilla to the deltoid, while originating in the upper trunk travels through the posterior cord and should show changes in the affected side.
Normal
Median, ulnar and musculocutaneous nerves would be unaffected in posterior cord lesions.

54. Some needle stuff
Posterior Cord Plexopathy: Radial, axillary, and thoracodorsal nerves are derived from the posterior cord.
Muscles affected:
latissimus dorsi,
deltoid, triceps,
brachii, anconeus,
brachioradialis, extensor carpi radialis longus,
Extensor carpi radialis brevis,
Supinator,
Extensor digitorum,
Extensor digiti minimi,
Extensor carpi ulnaris,
Abductor pollicis longus,
Extensor pollicis brevis,
Extensor pollicis longus,
Extensor indicis.

55. 5 3 3 5
Roots
Trunks
Cords
Branches/Nerves C5
Upper
Lateral
Musculocutaneous
LABC C6
Axillary
Radial
Middle
Posterior C7
Median C8
Ulnar
Lower
Medial T1
MABC

56. Medial cord plexopathies
Findings of medial cord lesions are the same as lower trunk lesions with one notable exception: the radial MNC.
Remember, the C8 motor fibers of the radial nerve go thru the lower trunk then the posterior cord while C8 and T1 motor fibers of the median and ulnar nerves also transverse the lower trunk, but these go thru the medial cord.
Therefore only median and ulnar innervated muscles will be affected in medial cord lesions.
DTR’s are normal

57. Nerve Conduction Studies
Sensory nerve conduction studies
Abnormal
Ulnar and medial antebrachial cutaneous nerves, are both C8/T1, lower trunk and medial cord nerves, thus they reveal reduced amplitudes as compared to the unaffected side.
Normal
Median sensory nerve, from C6/7, upper and middle trunks and lateral cord, remains normal

58. Nerve Conduction Studies
Motor nerve conduction studies
Abnormal
There would be decreased CMAP amplitude in both ulnar and median motor NCS, but this could be true in lower trunk and C8/T1 lesions as well.
Normal
Motor nerve conduction study of the radial nerve (C7/8, lower trunk, posterior cord) to the extensor indicis proprius would be symmetrical, side-to-side.

59. Some needle stuff
Medial Cord Plexopathy: Direct continuation of the anterior division of the lower trunk.
Muscles affected:
All ulnar muscles and
C8-T1median muscles.

60. 5 3 3 5
Roots
Trunks
Cords
Branches/Nerves C5
Upper
Lateral
Musculocutaneous
LABC C6
Axillary
Radial
Middle
Posterior C7
Median C8
Ulnar
Lower
Medial T1
MABC

61. Conclusion
Brachial plexus lesions and injuries can be most challenging.
When evaluating brachial plexus injuries, motor amplitudes may not add much to the diagnostic localization. However, sensory studies comparing the affected limb to the contralateral limb are helpful for anatomic localization, especially when determining localization as well as pre- and postganglionic injuries.

62. Questions