USMLE Step 1 Review 02 03 Anatomy Brachial Plexus Injuries Winged Scapula and Waiters Tip

USMLE Step 1 Review 02 03 Anatomy Brachial Plexus Injuries Winged Scapula and Waiters Tip

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Begin 02 03 Anatomy Brachial Plexus Injuries Winged Scapula and Waiters Tip Transcription

Injuries to nerves of the brachial plexus: The first key to this is to associate the symptoms with the part of a plexus or the particular nerve hurt.

What’s the nerve involved with winged scapula, accentuated when pushing against the wall?

  • The long thoracic nerve.

What muscle is innervated?

  • Serratus anterior muscle.

What’s a common cause of winged scapula caused by trauma to the long thoracic nerve? 

  • Carrying a very heavy load on the shoulder, crushing the long thoracic nerve between first rib and clavicle.

 What nerve is involved in anesthesia of lateral upper portion of the arm and partial or complete loss of AB-duction or anteversion of arm?

  • The axillary nerve.

What muscles are involved?

  • Primarily, the deltoid muscle.  Also, teres minor.

What does this often result from?

  • Shoulder dislocation.

What nerve is associated with a partial loss of abilities to depress the shoulder, AD-duct arm, or extend arm behind the back?

  • The thoracodorsal nerve.

What’s the muscle? 

  • Latissimus Dorsi.

What’s a common cause of injury to the thoracodorsal nerve? 

  • It’s vulnerable to injury during surgery to the axilla, such as in removal of axillary lymph nodes during breast cancer surgery.

What part of the brachial plexus is most probably affected in the following set of symptoms? 

  • Extensive and variable paralysis of shoulder and upper limb.  Waiter’s tip sign (which is the arm hanging down straight, rotated inward medially, and straight hand is adducted as if the hand is going backwards underneath to receive a tip from behind).

Included in the constellation of symptoms, variable anesthesia of upper back and upper limb?

  • Superior trunk of brachial plexus and can include nerve roots above.

There are three nerves most affected in injuries to superior trunk of the brachial plexus.  One is an extension of the lateral cord.  The other two terminal branches of the posterior cord.  What are they?

  • The musculocutaneous nerve, the axillary nerve, and the radial nerve.

What are some of the common causes of damage to the superior trunk of the brachial plexus?

  • Motorcycle accidents are the biggest. Also, falls on the shoulder in sports or other falls, violent stretching of an infant’s neck during delivery, and sometimes stab or bullet wounds to the neck.

The waiter’s tip sign involves 4 positions of the arm -what are they?

  • The arm hangs down, the arm hangs straight, the arm is rotated medially, and the straight hand is adducted.

What is lost when the arm hangs straight down?

  • Loss of AB-duction.

What is lost with the arm hanging straight, even a little hyperextended at the elbow?

  • Loss of flexion at the elbow.

And what is lost with the arm rotated medially?

  • Loss of lateral rotation of the arm.

What is lost with straight hand adduction?

  • Loss of extension at the wrist and loss of flexion in the fingers.

Let’s include the nerves and muscles now.

The arm hanging down – what two muscles are paralyzed so that we have loss of AB-duction?

  • Deltoid and supraspinatus.

What are the nerves?

  • The axillary to the deltoid and the suprascapular to the supraspinatus.

The arm hanging straight down where we have loss of flexion of forearm – what four muscles are paralyzed?

  • Biceps and brachialis muscles, coracobrachialis, and the brachioradialis.

And what are the nerves to those muscles?

  • Biceps and brachialis muscles and coracobrachialis muscle are all via the musculocutaneous nerve.  The brachioradialis muscle is by the radial nerve.

Now, the arm rotated medially (loss of lateral rotation of arm) – what two lateral rotators are paralyzed?

  • Teres minor and infraspinatus muscles.

What are the nerves innervating those?

  • Teres minor by the axillary nerve and infraspinatus by the suprascapular nerve.

The straight hand adducted where we have loss of hand extension gets a little complicated, but we’re going to leave it simple.  What is the nerve?

  • The radial nerve.

And what are the three most obvious muscles? 

  • Extensor carpi radialis longus and brevis, and extensor carpi ulnaris – all via the radial nerve.



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