Brachial/Lumbar plexopathies/median-ulnar-radial nerve anatomy

Question 1

Describe the anatomical course of the median nerve in the arm.

Answer 1

In the arm the median nerve is with the axillary/brachial artery as it descends distally in the arm. This bundle course somewhat anteriorly from the axilla, over the brachialis mm and medial intermuscular septum, until it reaches the antecubital fossa. By mid arm level the median nerve is no longer associated with any other neural structures. It is 1st located laterally, but then crosses the brachial artery to lie medial to it. (Good thing to know when stimulating it. In the antecubital fossa, the median nerve is associated with the brachial artery. At the elbow the median nerve lies on the brachialis tendons. Lateral to the median nerve is the biceps tendon and medially lies the pronator teres muscle.

Question 2

Describe the anatomical course of the median nerve in the forearm.

Answer 2

The median nerve enters the forearm by passing between the two heads(superficial/humeral heads) of the pronator teres muscle. In the forearm, the nerve is located between and posterior to the flexor digitorum superficialis muscle and anterior to the deep forearm flexor muscles. 5 cm proximal to the flexor retinaculum the median nerve lies just medial to the flexor carpi radialis and lateral to the palmaris longus tendons.

Question 3

What is the AIN nerve anatomical course.

Answer 3

Approx. 2-8 cm distal to the medial epicondyle, the AIN branches @ulnar deep/head of PT and courses distally and superficial to the flexor digitorum profundus mm.

Question 4

What is the last branch of the median nerve in the forearm?

Answer 4

The last branch given off main branch of median nerve in forearm is the palmar cutaneous branch 5-8cm proximal to the distal wrist crease.

Question 5

What NCV/EMG findings would you see with upper trunk lesion?

Answer 5

SNAP decreased: radial & median D1-D3 CMAP decreased: deltoid, biceps and supraspinatus EMG +: supra/infraspinatus, deltoid, biceps and brachioradialis; serratus/rhomboid/paraspinals normal

Question 6

What clinical findings would you see with middle trunk lesion (rare)?

Answer 6

Sensory loss of middle finger. Weakness of triceps, FCR and pronator teres C7 reflex is depressed

Question 7

What NCV/EMG findings would you see with middle trunk lesion?

Answer 7

SNAP decreased: D3 CMAP decreased: extensor indices EMG+: lat, pec major (lower sternal), serratus anterior

Question 8

What clinical findings would you see with lower trunk lesion?

Answer 8

(most likely will get a C8-T1 nerve root avulsion) weak structure Sensory loss of medial arm/forearm, hand and D4&D5 Weakness of grip

Question 9

What NCV/EMG findings would you see with lower trunk lesion?

Answer 9

SNAP: D5 and MABC CMAP: decreased APB and ADM, EI EMG: +APB, ADM, FDI, EI, lat

Question 10

What clinical findings would you find with a lateral cord lesion?

Answer 10

Sensory loss: lateral forearm, hand and D1-D3 Weakness of pronation, wrist and elbow flexion Biceps reflex decreased

Question 11

What NCV/EMG findings would you see with lateral cord lesion?

Answer 11

SNAP decreased: LABC, Median D1&D2 EMG: +FCR, PT, biceps Radial SNAP should be fine as it comes from UT and descends in Posterior Cord not lateral cord

Question 12

What clinical findings would you find with posterior cord lesion?

Answer 12

Sensory loss: lateral arm, posterior arm and forearm and radial dorsal hand Weakness: wrist/finger drop, arm/elbow extension, shoulder ABD and ADD(lat) Triceps and brachioradialis reflex decreased

Question 13

What NCV/EMG findings would you see with posterior cord lesion?

Answer 13

CMAP decreased: radial and deltoid EMG: +deltoid, teres minor, lat, elbow/wrist/finger extensors

Question 14

What clinical findings would you find with medial cord lesion?

Answer 14

Sensory loss: medial arm/forearm/hand and D4&D5 Weakness: grip

Question 15

What NCV/EMG findings would you find with medial cord lesion?

Answer 15

CMAP decreased: APB, ADM SNAP decreased: D4&D5 and MABC EMG: +APB, ADM, FDI, FPL, FDP

Question 16

Describe the carpal tunnel.

Answer 16

The carpal tunnel roof is the transverse carpal ligament pisiform and hook of hamate medially and scaphoid tubercle and trapezium bone laterally. Its contents include 8 tendons of FDS, FDP and FPL tendon.

Question 17

Where does the recurrent motor branch of median nerve arise from?

Answer 17

At the distal edge of the transverse carpal ligament a recurrent motor branch to innervate the thenar mass (APB, OP, SHFPB).

Question 18

Describe the anatomical course of the ulnar nerve in the arm.

Answer 18

in the proximal arm, it is positioned medial to the brachial artery while the median nerve is lateral to the vessel forming a neurovascular bundle. This bundle lies in the groove between the coracobrachialis muscle laterally and the 3 heads to the triceps posteriorly and anterior to the intermuscular septum. At the midportion of the upper arm the ulnar departs the neurovascular bundle and pierces the septum to enter the posterior compartment of the arm near the internal brachial ligament. The ulnar nerve then lies on the medial surface of the medial head of triceps mm in a deep groove (called the arcade of Struthers).

Question 19

Describe the anatomical course of the ulnar nerve in forearm.

Answer 19

Just proximal to the elbow/olecranon the ulnar nerve departs from the triceps and lies posterior to the medial humeral epicondyle and medial to the olecranon process (postcondylar groove). It then passes between the humeral and ulnar heads of the FCU. Distal to the cubital tunnel the nerve lies deep to the FCU and superficial to the FDP. Enters hand by passing superficial to tranverse carpal ligament and deep to thin volar carpal ligament between hook of hamate and pisiform ‘Guyon’s canal’. In Guyon’s canal the nerve divides into superficial and deep branch. The superficial branch innervates the palmaris brevis.

Question 20

Where does the dorsal ulnar cutaneous nerve arise?

Answer 20

5-10 cm proximal to the wrist the dorsal ulnar cutaneous nerve branches and goes posteriorly to between ulnar and tendon of the FCU, reaching dorsum of hand

Question 21

Where does the ulnar palmar cutaneous branch arise?

Answer 21

Proximal to the doral ulnar cutaneous nerve, the palmar cutaneous branch arises and supplies skin over the hypothenar eminence.

Question 22

What does the ulnar Proper palmar digital branch innervate?

Answer 22

medial aspect of 5th digit

Question 23

What does the ulnar Common palmar digital branch innervate?

Answer 23

the lateral aspect of D5 and medial aspect of D4

Question 24

Which nerve is the largest branch off the brachial plexus?

Answer 24

Radial nerve

Question 25

Describe the course of the radial nerve in the arm.

Answer 25

In the axilla, the radial nerve is posterior to the axillary artery, the nerve descends in a groove between the long and medial heads of the triceps, until it reaches the spiral groove. In the spiral groove it is deep to the lateral head of the triceps. Approx. 10 cm proximal to the lateral epicondyle it pierces the intermuscular septum entering the anterior compartment. It then continues distally between the brachialis and brachioradialis mms. In the lateral 3rd of arm it descends under the brachioradialis, ECRL and ECRB.

Question 26

Describe the course of the radial nerve as it crosses the elbow joint.

Answer 26

It then crosses the elbow joint and divides into the superficial radial and PIN prior to the supinator mm. The PIN enters the supinator via Arcade of Froshe and exits; courses under the forearm extensors distally, it finally provides branches to the carpal joints. The superficial radial nerve descends under the brachioradialis mm. It passes superficial to the supinator and flexor pollicis longus. It crosses the wrist joint to supply the lateral aspect of the hand’s dorsum.

Question 27

Can you diagram the course of the ulnar nerve and its branches through Guyon’s Canal.

Answer 27

Question 28

Is it common to have a lesion of the Lx and Sacral plexus at same time?

Answer 28

No, lesions do not normally affect both the Lx and sacral plexus at same time.

Question 29

What nerves make up the anterior division of LxSacral plexus?

Answer 29

Tibial, superior gluteal, inferior gluteal, peroneal

Question 30

What nerves make up the posterior division of the LxSacral plexus?

Answer 30

Femoral and obturator

Question 31

What are some nerves that contribute to the Lx plexus?

Answer 31

Femoral (innervates psoas), obturator, lateral femoral cutaneous nerve

Question 32

What are some nerves that contribute to the sacral plexus?

Answer 32

Tibial, superior gluteal, inferior gluteal, common peroneal and post cutaneous nerve of thigh.

Question 33

What is the largest nerve in the human body?

Answer 33

Sciatic nerve

Question 34

What are some Lx plexus SNAPs and CMAPs?

Answer 34

LFCN(L2-L3) and saphenous(L4) SNAPs, femoral CMAP (stim inguinal region and record at VMO)

Question 35

What are some sacral plexus SNAPs and CMAPs?

Answer 35

Sural, superficial peroneal SNAPs, tibial and peroneal CMAPs

Question 36

What type of plexopathy would you suspect with findings in femoral and obturator regions?

Answer 36

Lx plexopathy

Question 37

If you found fibs in superior/inferior gluteal nerves with normal paraspinals what plexopathy would you suspect?

Answer 37

Sacral plexopathy

Question 38

What clinical findings would you see with peroneal division lesion?

Answer 38

Footdrop, weak DF and EV, weak toe ext, numbness dorsum of foot

Question 39

What muscles and nerves are involved in someone with weak hip ext and abd?

Answer 39

Hip ext- glut max- inferior gluteal and Hip abd- glut med- superior gluteal

Question 40

What region does the sural nerve innervate?

Answer 40

Posterolateral leg and lateral margin of foot

Question 41

What type of things may cause a sciatic neuropathy?

Answer 41

Hip replacement and pelvic fracture. Glut max and med is spared in sciatic injury.

Question 42

What nerves could a hip dislocation compromise?

Answer 42

Peroneal and tibial nerves

Question 43

What nerves could a SIJ separation/dislocation compromise?

Answer 43

Sacral plexus and tibial nerves

Question 44

What would you suspect with acute onset of pain f/b mm weakness?

Answer 44

Neuralgic amyotrophy, spontaneous recovery

Question 45

What are some things that may cause a lumbosacral plexopathy?

Answer 45

Hx of pelvic tumor, radiation, trauma to pelvis or complicated delivery f/b weakness in lower limb

Question 46

What are CMAPs NMJ transmission time?

Answer 46

1.5ms; (latency of activation .5ms)+(NMJ transmission delay 1.0ms)

Question 47

If you look at CMAP amplitude 8 days post initial onset of sxs, what is the prognosis with a small amplitude vs large amplitude CMAPs?

Answer 47

Small amplitude- axonal loss- poor
Large amplitude- conduction block- good