Upper Limb Nerve Injuries

Question 1

Diagram of cutaneous nerve innervation in the upper limb:

Answer 1

Question 2

If the cell body of a neuron is injured, what occurs?

Answer 2

• Cell body/neuron dies.
• No regeneration occurs.

Question 3

Where are the cell bodies of motor neurons found?

Answer 3

ventral horn

Question 4

Where are the cell bodies of sensory neurons found?

Answer 4

dorsal root ganglia

Question 5

Compression of an axon may (2):

Answer 5

1. stimulate the axon
2. interfere with axon transmission

dependent on how hard and how long it is being compressed.

Question 6

Severe compression of an axon will lead to:

Answer 6

• death of the part of the axon distal to the compression.
• proximal part of the axon (closest to the cell body) will survive.
• regeneration can occur.

Question 7

Proximal-distal gradient of axonal regeneration:

Answer 7

• Return of function occurs in a proximal-distal gradient:
  
  • sever median nerve around elbow, proximal forearm muscles regain function first, followed by anterior forearm muscles and then hand.

Question 8

Surrounding each axon in the PNS is:

Answer 8

• endoneurium and Schwann Cells.

Question 9

Axonal regeneration following axon compression:

Answer 9

1. axon distal from the cell body and compression dies.
2. empty tube of Schwann Cells and endoneurium formed.
3. Schwann Cells become phagocytic and clean out the pathway for axon to regenerate.
4. regenerating axon grows along empty endoneurium pathway to the muscle cell that was denervated.

Question 10

Axonal regeneration following axon laceration:

Answer 10

1. axon distal from the cell body and laceration dies.
2. endometrium also lacerated.
3. suture epineurium back together in order to restore the pathway for the regenerating axon.

NOTE: you suture the epineurium together, not the endoneurium. The endoneurium is too small to suture together.

Question 11

Motor innervation of long thoracic nerve:

Answer 11

serratus anterior

Question 12

Contraction of the serratus anterior causes:

Answer 12

• protraction of the scapula, which moves the scapula ventrally around the thorax.

Question 13

Ways you can injure the LTN (3):

Answer 13

1. traction on the LTN by pulling the serratus anterior downward, or driving the scapula downward.
2. crush injury compressing the LTN against the thorax.
3. severing the LTN (common in breast lymph node biopsies).

Question 14

Damaging the LTN will lead to:

Answer 14

• weakness and/or paralysis of the serratus anterior muscle.
• limited range of motion in abduction and flexion of shoulder.

WINGED SCAPULA

Question 15

Axillary nerve motor and sensory innervations:

Answer 15

• motor innervations: deltoid and teres minor.
• cutaneous innervation: upper arm/shoulder area directly above the deltoid.

Question 16

Axillary nerve can be damaged via:

Answer 16

1. glenohumeral dislocation
2. dislocates inferior and anterior
3. surgical neck fracture (humerus)
   
   • commonly lead to displacement of the humerus. The deltoid pulls up on the distal end of the fragment, which causes it to override the proximal fragment.

Question 17

Chronic denervation of a muscle will lead to:

Answer 17

• atrophy of that muscle.

Question 18

Long term outcome of untreated axillary nerve damage due to glenohumeral dislocation or surgical neck fracture:

Answer 18

• atrophy of the deltoid
• will see protrusion of the acromion in the shoulder

Question 19

What is the most distal motor function of the radial nerve?

Answer 19

• Wrist extension (forearm extensor muscles).
• A good screening test for radial nerve injury.

Question 20

Radial nerve can be injured via (5):

Answer 20

1. upward pressure on floor of axilla.
2. glenohumeral dislocation.
3. mid-shaft humerus fracture.
4. radial head dislocation.
5. laceration or compression on radial side of wrist.

Question 21

If a patient exhibits wrist drop, what nerve is injured?

Answer 21

radial

Question 22

Radial nerve cutaneous innervation in the hand:

Answer 22

Question 23

Crutch injury and Saturday night palsy will lead to:

Answer 23

• Compression of the radial nerve in the axilla.
• Entire distribution of the radial nerve will be effected.
• All extensor function of arm and sensory innervation on hand.

Question 24

In general, the more distal the nerve injury, the:

Answer 24

• fewer the clinical findings.

Question 25

What is the most functionally debilitating loss due to median nerve injury?

Answer 25

* Loss of cutaneous sensory innervation in the palm of the hand on the radial 3.5 digits.

Question 26

Median nerve cutaneous innervation in the hand:

Answer 26

Question 27

Ways to injure the median nerve (6):

Answer 27

1. Elbow dislocation. 2. Supracondylar fracture. 3. Hypertrophy of the pronator teres, leading to median nerve compression. 4. Compression of the median nerve in the carpal tunnel. 5. Lunate dislocation. 6. Wrist laceration.

Question 28

Carpal tunnel contents:

Answer 28

* median nerve + 9 tendons go through the carpal tunnel.

Question 29

Pronator teres function:

Answer 29

**pronator and flexor** * in extreme flexing (weight-lifting), the pronator teres is * engaged and can hypertrophy. This can causemedian nerve compression.

Question 30

Distal median nerve injury manifestation in the hand (2):

Answer 30

1. loss of opposition (opponens pollicis) 2. claw hand first two digits (first two lumbricals)

Question 31

Proximal median nerve injury manifestation in the hand (1):

Answer 31

* sign of benediction * patient attempts to make fist, but the only two digits that can flex are the 4th and 5th digits since their flexion is mediated by the ulnar nerve in FDP.

Question 32

How to isolate and test the flexor digitorum profundus:

Answer 32

* hold PIP. * This is becauseonly the FDP crosses the DIP.

Question 33

How to isolate and test the flexor digitorum superficialis:

Answer 33

* pull back on the 2, 4, and 5 digits, and flex the middle finger. * This is only FDS since the FDP has one common tendon while the FDS has individual tendons for each digit.

Question 34

Manifestations of Carpal Tunnel Syndrome:

Answer 34

* clawing * thenar atrophy (chronic phase) * More common in post-menopausal women, and at night.

Question 35

Cutaneous innervation of the ulnar nerve in the hand:

Answer 35

Question 36

Places the ulnar nerve can be injured:

Answer 36

* medial epicondyle * palmar carpal ligament (at wrist) * in Guyon's canal next to the Hook of Hamate

Question 37

Manifestations of ulnar nerve injury (3):

Answer 37

1. clawing of the 4th and 5th digits since the lumbricals controlling these digits are innervated by the ulnar nerve. 2. interosseous atrophy since all interossei are innervated by the ulnar nerve. * the most visible is the first dorsal interosseous. 3. loss of abduction and adduction of the digits.

Question 38

Manifestations of upper trunk injuries:

Answer 38

* Waiter's tip sign: * limb at rest will be be adducted and internally rotated. The palm will be facing posteriorly.

Question 39

Muscles weakened/paralyzed by an upper trunk injury:

Answer 39

* abductors, flexors, and external rotators. * will lead to adducted and internally rotated wrist at rest.

Question 40

All of the intrinsic hand muscles are innervated by what roots?

Answer 40

* C8 and T1 (regardless of whether median or ulnar nerve)

Question 41

Lower trunk (C8/T1) injuries can be due to (2):

Answer 41

1. cervical rib (thoracic outlet syndrome) 2. upward traction of the limb

Question 42

Horner’s Syndrome:

Answer 42

* Damage to the T1 cervical root due to ta lower trunk injury. * T1 is part of the sympathetic nervous system outflow (parasympathetic chain). * If you injure a T1 spinal nerve you will effect the sympathetic innervations in the head.