The Brachial Plexus – anatomy, lesions and neurophysiology studies

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 Cords Branches/Nerves Trunks 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 Cords Branches/Nerves Trunks 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 Cords Branches/Nerves Trunks 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 Cords Branches/Nerves Trunks 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 Cords Branches/Nerves Trunks C5 Upper Lateral Musculocutaneous Axillary C6 Radial Middle Posterior C7 Median C8 Ulnar Lower Medial 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 carpiradialis (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 digitorumcommunis and extensor indicispropriusas 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 Axillary C6 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 • serratusanterior 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 Axillary C6 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 Axillary C6 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 • Abnormal • 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). • Normal • 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 digitorumprofundis, lumbrical muscles, opponensdigitiminimi, flexor digitiminimi, abductor digitiminimi, interossei, adductor pollicis), in addition to • median C8-T1 muscles (abductor pollicisbrevis, flexor pollicislongus, flexor digitorumprofundus), and • radial C8 innervated muscles (extensor indicisproprius and extensor pollicisbrevis).

45. 5 3 3 5 Roots Trunks Cords Branches/Nerves C5 Upper Lateral Musculocutaneous LABC Axillary C6 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 brachioradialisspared

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 Axillary C6 Radial Middle Posterior C7 Median C8 Ulnar Lower Medial T1 MABC