Upper Limb Nerve Injuries Flashcards
Diagram of cutaneous nerve innervation in the upper limb:
If the cell body of a neuron is injured, what occurs?
- Cell body/neuron dies.
- No regeneration occurs.
Where are the cell bodies of motor neurons found?
ventral horn
Where are the cell bodies of sensory neurons found?
dorsal root ganglia
Compression of an axon may (2):
- stimulate the axon
- interfere with axon transmission
dependent on how hard and how long it is being compressed.
Severe compression of an axon will lead to:
- 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.
Proximal-distal gradient of axonal regeneration:
- 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.
Surrounding each axon in the PNS is:
- endoneurium and Schwann Cells.
Axonal regeneration following axon compression:
- axon distal from the cell body and compression dies.
- empty tube of Schwann Cells and endoneurium formed.
- Schwann Cells become phagocytic and clean out the pathway for axon to regenerate.
- regenerating axon grows along empty endoneurium pathway to the muscle cell that was denervated.
Axonal regeneration following axon laceration:
- axon distal from the cell body and laceration dies.
- endometrium also lacerated.
- 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.
Motor innervation of long thoracic nerve:
serratus anterior
Contraction of the serratus anterior causes:
- protraction of the scapula, which moves the scapula ventrally around the thorax.
Ways you can injure the LTN (3):
- traction on the LTN by pulling the serratus anterior downward, or driving the scapula downward.
- crush injury compressing the LTN against the thorax.
- severing the LTN (common in breast lymph node biopsies).
Damaging the LTN will lead to:
- weakness and/or paralysis of the serratus anterior muscle.
- limited range of motion in abduction and flexion of shoulder.
WINGED SCAPULA
Axillary nerve motor and sensory innervations:
- motor innervations: deltoid and teres minor.
- cutaneous innervation: upper arm/shoulder area directly above the deltoid.
Axillary nerve can be damaged via:
- glenohumeral dislocation
- dislocates inferior and anterior
- 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.
Chronic denervation of a muscle will lead to:
- atrophy of that muscle.
Long term outcome of untreated axillary nerve damage due to glenohumeral dislocation or surgical neck fracture:
- atrophy of the deltoid
- will see protrusion of the acromion in the shoulder
What is the most distal motor function of the radial nerve?
- Wrist extension (forearm extensor muscles).
- A good screening test for radial nerve injury.
Radial nerve can be injured via (5):
- upward pressure on floor of axilla.
- glenohumeral dislocation.
- mid-shaft humerus fracture.
- radial head dislocation.
- laceration or compression on radial side of wrist.
If a patient exhibits wrist drop, what nerve is injured?
radial
Radial nerve cutaneous innervation in the hand:
Crutch injury and Saturday night palsy will lead to:
- 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.
In general, the more distal the nerve injury, the:
- fewer the clinical findings.
What is the most functionally debilitating loss due to median nerve injury?
- Loss of cutaneous sensory innervation in the palm of the hand on the radial 3.5 digits.
Median nerve cutaneous innervation in the hand:
Ways to injure the median nerve (6):
- Elbow dislocation.
- Supracondylar fracture.
- Hypertrophy of the pronator teres, leading to median nerve compression.
- Compression of the median nerve in the carpal tunnel.
- Lunate dislocation.
- Wrist laceration.
Carpal tunnel contents:
- median nerve + 9 tendons go through the carpal tunnel.
Pronator teres function:
pronator and flexor
- in extreme flexing (weight-lifting), the pronator teres is
- engaged and can hypertrophy. This can causemedian nerve compression.
Distal median nerve injury manifestation in the hand (2):
- loss of opposition (opponens pollicis)
- claw hand first two digits (first two lumbricals)
Proximal median nerve injury manifestation in the hand (1):
- 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.
How to isolate and test the flexor digitorum profundus:
- hold PIP.
- This is becauseonly the FDP crosses the DIP.
How to isolate and test the flexor digitorum superficialis:
- 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.
Manifestations of Carpal Tunnel Syndrome:
- clawing
- thenar atrophy (chronic phase)
- More common in post-menopausal women, and at night.
Cutaneous innervation of the ulnar nerve in the hand:
Places the ulnar nerve can be injured:
- medial epicondyle
- palmar carpal ligament (at wrist)
- in Guyon’s canal next to the Hook of Hamate
Manifestations of ulnar nerve injury (3):
- clawing of the 4th and 5th digits since the lumbricals controlling these digits are innervated by the ulnar nerve.
- interosseous atrophy since all interossei are innervated by the ulnar nerve.
- the most visible is the first dorsal interosseous.
- loss of abduction and adduction of the digits.
Manifestations of upper trunk injuries:
- Waiter’s tip sign:
- limb at rest will be be adducted and internally rotated. The palm will be facing posteriorly.
Muscles weakened/paralyzed by an upper trunk injury:
- abductors, flexors, and external rotators.
- will lead to adducted and internally rotated wrist at rest.
All of the intrinsic hand muscles are innervated by what roots?
- C8 and T1 (regardless of whether median or ulnar nerve)
Lower trunk (C8/T1) injuries can be due to (2):
- cervical rib (thoracic outlet syndrome)
- upward traction of the limb
Horner’s Syndrome:
- 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.
