Anatomy: UL Brachial Plexus

What is the general sequence (without branches) of the brachial plexus? RTDCN.

C5-T1 form the nerve roots. C5-C6 form the superior trunk, C7 forms the middle trunk, and C8-T1 form the inferior trunk. All trunks give nerves to the posterior cord. The superior and middle cord give rise to the lateral cord (anterior division) and the inferior cord becomes the medial cord. The lateral cord's terminal branches are the musculocutaneous nerve and a portion of the median nerve. The medial cord becomes the ulnar nerve and a portion of the median nerve. The posterior cord becomes the axillary and radial nerves.

Where does the ulnar nerve run?

Doesn't branch in the upper arm. Runs in the ulnar groove near the medial epicondyle and is subject to potential injury during medial epicondyle fractures.

What are the pre-plexus nerves? Where can they be found?

Dorsal scapular and long thoracic nerves. The dorsal scapular can be found by finding the levator scapulae, rhomboid minor and major muscles and then finding the nerve that passes through them. The long thoracic runs on the surface of serratus anterior.

What region is tested when an acute axillary nerve injury is suspected?

Following shoulder dislocation or proximal humeral fracture, the lateral portion of the shoulder is tested for sensory numbness.

What is the nerve coming off of the lateral cord prior to termination? Innervation?

Lateral pectoral which innervates the pectoralis major (inferior 2/3).

What are the nerves coming off of the medial cord prior to termination? Innervation of those nerves?

Medial pectoral - pectoralis minor and major. Medial brachial cutaneous - cutaneous only to medial arm. Medial antebrachial cutaneous - cutaneous only to medial forearm.

What are the terminal branches of the medial cord? What do they innervate?

Median nerve - Muscles of the anterior compartment (flexors), thenar muscles, sensory to palmar skin. Ulnar nerve - FCU and intrinsic hand muscles minus thenar.

What nerve innervates the anterior compartment of the arm?

Musculocutaneous nerve.

What is the important landmark of the brachial plexus when finding divisions?

Subclavian artery.

What is the nerve coming off of the superior trunk?

Suprascapular. Innervates supraspinatus and infraspinatus muscles of the rotator cuff.

What relationship between the axillary nerve and the humerus makes it clinically important?

The axillary nerve encircles the surgical neck of the humerus making it vulnerable to injury in proximal humeral fractures at the surgical neck. *****Injury to this nerve would result in flexion, abduction, and extension dysfunction within the arm****

What runs with the radial nerve in the radial groove?

The deep brachial artery.

What nerve innervates the posterior compartment of the arm?

Radial nerve.

What muscles do the brachial plexus nerves pass in between?

Anterior and middle/posterior scalene muscles.

What are the terminal branches of the posterior cord? What do they innervate (cutaneous + motor)?

Axillary - Motor to Deltoid and teres minor. Sensory to the superior lateral cutaneous to the lateral and posterior shoulder. Radial - Motor to the triceps brachii, anconeus, brachioradialis, and ECRL. Deep branch of radial to rest of posterior compartment muscles (extensors). Radial sensory to the dorsal 1st and 2nd web space.

What is significant about testing the lateral antebrachial cutaneous nerve?

Because its the most distal point of the musculocutaneous nerve (and thus the origins of), if sensory testing of this region is good, the nerve is intact back to the nerve root.

What occurs as a result of an injury to the radial nerve?

Loss of wrist extension, finger extension at the MP joints, and thumb extension. Hook'em horns sign indicates the nerve is intact to the nerve roots.

What is the course of the median nerve within the arm?

Passes anterior to the medial epicondyle where it is vulnerable to injury in epicondylar fractures. Doesn't innervate anything within the upper arm. Travels all the way to the tarsal tunnel.

What is the course of the radial nerve within the arm?

Terminal branch of the posterior cord that runs in the radial groove the humerus. After exiting the radial groove, it pierces the lateral intermuscular septoum to enter the anterior compartment. IT lies between the proximal brachialis and brachioradialis. The deep radial enters the cubital fossa and divides to form the superficial (sensory/cutaneous) and deep (motor) branches as it enters the cubital fossa. The deep radial becomes the posterior interosseous when it penetrates the supinator.

What is known if the patient has normal sensory testing in the snuff box but he or she cannot extend the index, small fingers, or thumb?

The neuro deficit or injury is distal to the bifurcation just proximal to the elbow (after the split to deep and superficial).

Where does the supraspinatus nerve run?

Traverses the scapular notch.

What are the nerves coming off of the posterior cord prior to termination? Innervation?

Upper subscapular - superior subscapularis Thoracodorsal - latissimus dorsi Lower subscapular - inferior subscapularis and teres major. NO cutaneous innervation.