USMLE Step 1 Review 02 04 Anatomy Brachial Plexus Injuries: Wrist Drop and Claw Hand

USMLE Step 1 Review 02 04 Anatomy Brachial Plexus Injuries: Wrist Drop and Claw Hand


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Begin 01 02 04 Anatomy Brachial Plexus Injuries: Wrist Drop and Claw Hand Transcription

Continuing with injuries to brachial plexus nerves:

In this next set of symptoms, what are the dermatomes involved?

  • Impairment of wrist flexion and of digital movements, anesthesia medial side of arm forearm and hand.  The C8 and T1 dermatomes.

What is the dermatome of the medial side of the arm?

  • T1.

What dermatomes are on the medial side of forearm and hand?

  • C8 and T1.

What general part of the brachial plexus are C8 and T1?

  • The lower brachial plexus.

Which of the terminal branches is the nerve that only has C8 and T1 in it?

  • The ulnar nerve.

If C8 and T1 are damaged, and the ulnar nerve is then paralyzed, which flexor of the wrist is innervated by ulnar is also going to be paralyzed?

  • Flexor carpi ulnaris.

In addition, two other terminal branches of the brachial plexus receives C8 and T1.  One of them only receives C8, and other receives C8 and T1.  What are these? 

  • The radial nerve receives C8.  The median nerve receives C8 and TI.

With ulnar nerve knocked out, and C8 and T1 missing from radial and median nerves, what is going to be affected in the hand?

  • Various digital movements.

We’re going to look at wrist drop and loss of triceps reflex.  Wrist drop is loss of hand extension.  What nerve is implicated?

  • Radial nerve.

What 3 muscles?

  • Extensor carpi radialis longus and brevis, and extensor carpi ulnaris.

In loss of triceps reflex, what nerve is implicated?

  • Radial nerve.

What are the two muscles?

  • Triceps and anconeus.

What is wrist drop often a sign of?

  • Radial nerve entrapment. The most common site is compression of radial in the middle of the arm often from sleeping on the arm especially when intoxicated.  This is also known as Saturday night palsy.

What nerve is involved in claw hand (when there’s no flexion of the 4th and 5th fingers and apofenanr atrophy? 

  • The ulnar nerve.

What are the levels?

  • C8, T1.

How does this happen? 

  • As the ulnar nerve passes posteriorly to the medial condyle of the elbow, it is often damaged when the elbow is traumatized and the medial epicondyle of the humerus is fractured.

What nerve is involved in numbness and tingling only on the medial side of the palm (the side opposite the thumb) and the 4th and 5th fingers?  Think of the dermatome and you’ll know the answer. 

  • The ulnar nerve, C8, T1.

What is this caused by? 

  • Ulnar nerve entrapment.  Compression at the elbow is common.

What nerve is involved in no thumb opposition, phenar atrophy, no flexion in thumb, index, or middle fingers? 

  • The median nerve, C6 to T1.

How does this happen?

  • The median nerve is often cut proximal to flexor retinaculum from suicide attempts by slashing the wrists with a razor blade, and this affects only these hand structures.

When you have pain and tenderness in the proximal portion of the anterior forearm often following repetitive elbow movements, what nerve is affected? 

  • The median nerve, C6 to T1.  But, compressed in a different location.

How does this often happen?

  • This is caused the pronator syndrome.  The median nerve is then trapped near the elbow between the two heads of the pronator teres muscles due to trauma or repetitive motion injury.

What nerve is involved in loss of elbow flexion and forearm supination and loss of biceps reflex as an isolated set of symptoms? 

  • The musculocutaneous nerve.

What are the 3 muscles involved?

  • Biceps and brachialis and coracoids brachialis muscles.

How does this occur?

  • When the musculocutaenous nerve is severed in the axilla before it has innervated any of the muscles in the arm for flexing and supinating the forearm.

What part of the brachial plexus is involved in temporary numbeness and tingling in the upper limbs and temporary impairment in upper limb motor function?

  • This is characteristic of compression of inferior trunk of the brachial plexus.

This usually involves what 3 nerves? 

  • Sensory and motor portions of ulnar, radial, and median nerves.

What two sensory nerves coming off the inferior part of the brachial plexus are implicated by the temporary numbness and tingling?

  • The medial antebrachial cutaneous nerve and the medial brachial cutaneous nerve coming off the cord.

How is this caused?

  • This is characteristic of thoracic outlet syndrome or cervical rib syndromes, where temporary compression of inferior trunk occurs while carrying a weight with arm hanging, such as when carrying a suitcase, or while performing a repetitive motion with the arm in a raised position.



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