Brachial plexus: anatomical course and lesions

This issue has come up in  Question 14.3from the first paper of 2013. The candidates were invited to differentiate between an ulnar nerve injury and a lower brachial plexus injury in a patient who had returned from cardiac surgery.

The images and text content in included below for the purposes of rapid revision.

However, as far as point-form summaries from an authoritative source are concerned, Wheeless' Textbook of Orthopaedics does it much better.

Structure of the Brachial Plexus

Relations of the Brachial Plexus

Supply distribution of the brachial plexus

Lesions of the Brachial Plexus

Erb's palsy: upper brachial plexus injury

• arm cannot be raised, since deltoid (axillary nerve ) & spinati muscles (suprascapular nerve) are paralyzed
• elbow flexion is weakened because of weakness in biceps & brachialis;
• weakness in retraction and protraction of scapula - due to paralysis of rhomboids and serratus anterior, if roots are damaged above their junction
• Lateral arm loses sensation
• "Waiter's Tip" position, where the limb hangs limp in a medially rotated position
• Usually caused by an increased angle between neck and shoulder, eg. falling on your head.

Compression of the cords

• Pain radiating dfown the arm
• Hand numbness
• Hand weakness
• Caused by prolonged hyperabduction, eg. painting the ceiling; cords get pinched between coracoid process and pectoralis minor tendon.

Klumpke paralysis: lower brachial plexus injury

• Weakness in intrinsics of hand as well as long flexors & extensors of the fingers, and you get a "claw hand"
• A sensory deficit ialong the medial aspect of the arm, forearm, hand
• Associated Horner's syndrome
• Caused when the arm is suddenly pulled superiorly, eg. when you grab something while falling vertically down.