Brachial Plexus

Question 1

Where does the brachial plexus arise from?

Answer 1

The ventral primary rami of spinal nerve roots C5-T1

Question 2

Thoracic outlet syndrome (TOS)

Answer 2

The space between your clavicle and first rib is compressed compressing the brachial plexus with it. This can cause numbness and tingling in the arm

Question 3

Dorsal scapular nerve

Answer 3

(C4) C5

Innervates rhomboid major and minor and occasionally supplies a branch to the levator scapulae

Accompanied by branches of the transverse cervical artery

Muscle tests: position of attention (retraction of scapulae)
Muscle testing of the rhomboids can distinguish upper plexus injuries from C5 nerve root injuries. In a spinal nerve root injury the weakness will be more diffuse than if the injury is to the upper plexus. It may also be very difficult to see atrophy of the rhomboids given the overlying trapezius muscle

Question 4

Long thoracic nerve

Answer 4

C5, 6, 7 (c8)

Innervates the serratus anterior

Possible compression occurs between the anterior and middle scalene resulting in weakness of the serratus (scapular winging)

Muscle test: reach test, scapular winging on performing a push-up or pushing against the wall.

Question 5

Long thoracic nerve syndrome

Answer 5

Possible causes include: caring heavy backpacks on the shoulders, poorly fitted crutches, tight casts, or blows to the shoulder, Lyme disease, and axillary surgery

Causes paresis of shoulder abduction and elevation (serratus anterior function), vague shoulder weakness and pain, difficulty with overhead tasks and lifting arms straight up, winging of the scapula, abnormal scapular movements

Question 6

Subclavius innervation

Answer 6

C5, 6

Functionally, this is an anterior division nerve, from the upper trunk of the brachial plexus.

Muscle test: patient holds arm up and tight to the side of their head with palm facing out while the examiner pulls their arm away from the head

Injuries to the upper trunk may caused weakness of the subclavius and weakness of the subclavius may also contribute frozen shoulder syndrome. Strengthening this muscle by isometric contraction can be very helpful.

When the subclavius is weak, the shoulder muscles are often dysfunctional as the clavicle is unstable

Question 7

Suprascapular nerve

Answer 7

(C4), C5, (C6)

Innervates the supraspinatus muscle (and the infraspinatus muscle)
Provides sensory fibers to the acromioclavicular joint as well as the glenohumeral joint

Muscle test: shoulder abduction. Patient’s arm extended at their side with about 15° of abduction and a bit anterior. The palm should be facing the area of the groin. The patient hold this position while the examiner pushes arm in toward the midline against the patient’s resistance

Question 8

Suprascapular nerve

Answer 8

(C4), C5-6

Innervates the infraspinatus muscle

Muscle test: external rotation of the shoulder

Super scapular nerve syndrome: entrapment at the super scapular notch often as a result of overuse injuries, such as strenuous overhead activities (Volleyball serving and hitting) or work postures. Sleeping with the arm overhead or holding a cell phone between the head and shoulder can also put a great deal of stress on the nerve. Other causes include resting heavy objects on the shoulder, scapular fracture, and arthrodesis of the shoulder.

Question 9

Lateral pectoral nerve

Answer 9

C5, 6, 7

Derived from the lateral cord of BP

Innervates the upper and lower fibers of the pectoralis major

Muscle tests: shoulder flexion, abduction, and internal rotation

Question 10

Medial pectoral nerve

Answer 10

(C6,7), C8, T1

Innervates the lower fibers of the pectoralis major in the pectoralis minor

Muscle test: shoulder abduction and internal rotation (pec minor)

The pec minor is a primarily involved as an accessory inspiratory muscles of respiration and stabilizer of the scapula. Spasm or hyper trophy of the pectoralis minor muscle is an important contributor to the Costco pick Torrell space form of thoracic outlet syndrome, especially when the patient’s primary symptoms involve the lower trunk and inferior cord branches

Question 11

Lower subscapular nerve

Answer 11

C5, 6, (C7)

Innervates the teres major (C6) and subscapularis muscles (C5)

Muscle tests: extension, adduction (teres major) and internal rotation (subscapularis)

Question 12

Thoracodorsal nerve

Answer 12

C6, 7, 8

Innervates the latissimus dorsi

Muscle tests: adduction, internal rotation and extension of the shoulder

Question 13

Musculocutaneous nerve

Answer 13

C5, 6, 7

Innervates: biceps (C5,6), Brachialis (C5,6), Coracobrachialis (C5, 6, 7)

Cutaneous contribution: lateral antebrachial cutaneous nerve. Distribution to the lateral forearm, largely from C6. The C6 dermatome continues down to the thumb and includes the web. This is an important distinction when differentiating damage to the musculocutaneous or to C6

Question 14

Axillary nerve

Answer 14

C5, 6

Innervates: deltoid (C5, 6) and Teres Minor (C6)

Neurological level: deltoid, C5

Cutaneous contribution: superior lateral cutaneous nerve: regimental badge area

Quadrangular space syndrome: weakness of the deltoid and teres minor. Paresthesia in the “regimental badge“ area is noted. No loss of biceps reflex

Question 15

Median nerve

Answer 15

C6-T1

Innervates: pronator teres (C5-6), flexor carpi radialis (C6-7), Palmaris longus (C7-8), flexor digitorum superficialis

Possible entrapment: pronator teres and carpal tunnel

Question 16

Anterior interosseous nerve

Answer 16

Branch of the median nerve

Innervates:

• flexor digitorum profundus (median nerve portion, digits 2,3): C7-T1
• Flexor pollicis longus: C7-T1
• pronator quadratus: C8-T1

Entrapment tests: The sign of benediction in the sign of OK 👌

Question 17

Recurrent branch of the median nerve

Answer 17

(C8-T1)

Innervates: abductor pollicis brevis, flexor pollicis brevis (superficial head), Opponens pollicis

Question 18

Palmer digital branch of the median nerve

Answer 18

(C8-T1)

Innervates: lumbricals I and II of digits I and III (thumb has no lumbricals)

Question 19

Ulnar nerve

Answer 19

C8-T1

Innervates: flexor carpi ulnaris, flexor digitorum profundus (ulnar portion), Thenar eminence (adductor pollicis and flexor pollicis brevis), hypothenar eminence (Palmaris brevis, abductor digital minimi, flexor digitorum anime, opponents Digitimer am I, lumbricals III and IV, PAD & DAB)

Cutaneous: The Palmer cutaneous branch (medial half of the palm), The dorsal cutaneous branch (anterior and posterior aspect of the medial 1 1/2 fingers)

Tunnel of guyon syndrome and cubital tunnel syndrome from entrapment

Question 20

Radial nerve

Answer 20

C5-T1

Innervates: triceps, Anconeus, brachioradialis (C5, 6), supinator (C6), extensor carpi radialis longus (C6, 7)

Cutaneous innervations: The lower lateral cutaneous nerve, the posterior brachial cutaneous nerve, the posterior antibrachial cutaneous nerve, the superficial radial nerve

Radial nerve syndrome: Saturday night palsy: Muscular weakness of the wrist extensors (wrist drop)

Question 21

Deep radial nerve (a.k.a posterior interosseous nerve)

Answer 21

Muscles innervated: 
extensor carpi radialis brevis 
Extensor carpi ulnaris 
Extensor digitorum 
Extensor digitorum minimi
Extensor indicis 
Extensor pollicis longus
Extensor pollicis brevis
Abductor pollicis longus

Entrapment: posterior interosseous nerve syndrome (entrapment at the arcade of frohse) Present mainly is muscle weakness, there’s weakness of rest, finger, and thumb extension, especially extension of the third digit. There are no parastesis as there are no cutaneous branches of this nerve