Upper extremity nerves Flashcards
What are the 5 parts the brachial plexus is broken into (I.e. its subdivisions)?
Rad Techs Drink Cold Beer
Roots (there are 5)
Trunks (3)
Divisions (2)
Cords (3)
Branches (5)
Brachial plexus roots
Ventral rami of C5-T1 spinal nerves
There are anatomic variants - sometimes C4 contributes to brachial plexus without much from T1 (prefixed brachial plexus). Sometimes T2 contibues to brachial plexus without much from C5 (postfixed)
Most common variant is C5-C6 root passing anterior to or through anterior scalene muscle
Describe the anatomy leading up to the ventral ramus
Ventral (motor) and dorsal (sensory) roots from cord course into neural foramen where they merge to form the spinal nerve. The neural foramen is basically the origin of the brachial plexus.
Neural formanen approximates the location of dorsal root ganglion - bulbous structure along dorsal root located just proximal to union of ventral and dorsal roots. Contains first order sensory nerve cell bodies. It’s a landmark for pre-vs-post ganglion injury
Distal to neural foramen, the spinal nerve divides into ventral and dorsal rami. Dorsal rami extend posteriorly to innervate paraspinal muscles. ventral rami are the roots of the brachial plexus and course anteriorly towards interscalene triangle.
What do the roots of the BP look like on MR? What’s an important landmark to help find them?
Five stacked points on sagittal images.
Look for the proximal aspect of the first rib on sagittal. T1 root is below the rib. C8 root is above.
What is the interscalene triangle?
Formed by anterior and middle scalene muscles. The muscles originate from anterior and posterior tubercles of the c spine transverse processes and insert onto the first rib. Anterior scalene is from C3-6 processes. Middle is from C2-C6. Anterior inserts anteriorly on rib 1. Middle inserts posterolaterally.
Subclavian artery is within this triangle
Within medial aspect of triangle - C5-C7 roots are superior to artery. C8-T1 roots are posterior to artery.
Along lateral border of middle scalene and lateral aspect of the triangle, the 3 trunks can be detected.
Where do the trunks of the BP originate and what are they?
Trunks originate from the roots within the lateral aspect of the interscalene triangle.
Upper trunk - formed by union of C5 and C6 roots
Lower trunk - formed by union of C8 and T1 roots
Middle trunk - continuation of C7 root.
Upper and middle trunks are above the subclavian artery. Lower trunk is posterior.
The trunks look like 3 stacked points on sagittal images
Where do the BP divisions originate and what are they?
As the trunks continue inferolaterally, each trunk separates into an anterior and posterior division at or near the lateral border of the first rib.
This is the same location subclavian artery becomes axillary artery.
together the anterior and posterior divisions of the 3 trunks make a triangular cluster of 6 points just superior to the axillary artery and posterior to the midclavicle
What is the function of BP divisions?
Anterior divisions innervate flexor muscles of upper limb
Posterior divisions innervate extensor muscles of upper limb
Where do the BP cords originate and what are they?
As divisions continue inferolaterally, they make 3 cords - lateral, posterior, and medial cords. Theyre named after their relation to axillary artery. Cords appear at medial border of coracoid process.
The 3 cords + axillary artery make a paw print appearance on sagittal images.
Posterior cord is located between the lateral and medial cords.
Flexor muscle innervation comes from branches of lateral and medial cords
Extensor muscle innervation comes from branches of posterior cord
BP terminal branches
At lateral border of pectoralis minor muscle the cords separate into 5 terminal branches.
Posterior cord - gives off a branch posteriorly, looping under scapular neck to become axillary nerve
The remaining four branches are centered around the axillary or brachial artery.
Median nerve - anterior superior quadrant around the artery
Musculocutaneous nerve - posterior superior quadrant
Radial nerve - posterior inferior
Ulnar nerve - anterior inferior
What are some other nerves that come off the BP?
Phrenic nerve
Long thoracic nerve
Dorsal scapular nerve
Suprascapular nerve
Phrenic nerve - where does it come from and what does it innervate?
From C3-C5 roots and turns anteriorly to pass through or around anterior scalene muscle between subclavian vein and artery as it passes inferiorly into middle region of mediastinum
It is motor supply of diaphragm. sensory fibers to fibrous pericardium, mediastinum, pleura, and diaphragmatic peritoneum
Long thoracic nerve - origination and innervation
From C5-C7 roots and turns posteriorly to pass through or around middle scalene muscle before going down posteriorly to the brachial plexus along surface of serratus anterior muscule. Long course and superficial location means it is prone to injury.
Motor nerve to serratus anterior. Responsible for shoulder protraction (during punching) and upward rotation of scapula during lifting.
Injury leads to winging of scapula. Injury can be from viral illness, repetitive use (athletes, digging, arm stuck in abduction propping up back of head for too long - like while reading), or from mastectomy from LN dissection, single axillary crutch
Dorsal scapular nerve - origin and innervation
From C5 root. It turns posteriorly to pass through middle scalene muscle before continuing inferiorly deep to levator scapulae
Supplies levator scapulae and rhomboid major/minor. These are periscapular stabilizing muscles.
Can become entrapped by hypertrophied middle scalene muscle. Lead to winging of scapula
Suprascapular nerve - origin and innervation
From the upper trunk at Erb point. It travels laterally along posterior border of the clavicle, turning posteriorly at the superior margin of the scapula to pass through the suprascapular notch before continuing into supraspinatus fossa.
At suprascapular notch the nerve passes under the superior transverse scapular ligament (suprascapular artery goes OVER ligemant). Injury or compression (cysts) here would lead to SS and IS denervation. It continues inferiorly and passes through spinoglenoid notch into infraspinatus fossa. Injury or compression here would lead to IS denervation only.
Motor to supraspinatus and infraspinatus
Sensory to glenohumeral and acromioclavicular joints
See figure
Axillary nerve course and branches
Terminal branch of brachial plexus from C5-C6 posterior cord
Travels through quadrilateral space along with posterior circumflex artery and vein
Mixed motor and sensory
Branches: Anterior, Posterior, and intra-articular branches, lateral cutaneous nerve of arm
At quad space - branch to shoulder joint
Anterior branch - Ant deltoid
Posterior branch - Post deltoid + teres minor. After this the axillary n goes around the lower border of the deltoid and is then called superior lateral cutaneous nerve of the arm - skin of lower deltoid and upper part of long triceps
Articular branch - GH joint
Intra-articular branch - GH joint
Quadrilateral space boundaries
Floor - teres major
Roof - teres minor
Lateral - surg neck of humerus
Medial - long head triceps
Radial nerve course
From posterior cord BP along with axillary nerve. It’s the largest upper extremity nerve
Posterior to axillary nerve and btw coracobrachilias and teres major. Descends between lateral and medial heads of triceps. Through radial groove of humerus. For most of its course it runs with brachial artery.
Wraps around distal humerus and goes anterior to lateral condyle where it penetrates lateral intramuscular septum.
Upon crossing cubital fossa it branches into its terminal branches: superficial (sensory) and deep (motor).
Ulnar nerve course
It’s the distal continuation of medial cord of BP. It is medial to axillary artery. It descends along medial arm, medial to brachial artery and biceps brachii.
In the mid arm It pierces medial intermuscular septum to enter posterior compartment. Here it runs anterior to medial head triceps under arcade of struthers
Then it goes between medial epicondyle and olecrenon in groove for ulnar nerve into the anterior compartment of forearm.
Ulnar nerve typically has no branches in the arm.
Then it runs through cubital tunnel, superficial to the posterior and oblique bands of the UCL. here it gives off articular branches to elbow joint.
Continues into forearm by passing btw humeral and ulnar heads of FCU. In forearm we get 2 muscular branches to FCU and ulnar part of flexor dig profundus (the lateral part of FDP and the rest of the anterior compartment are supplied by median nerve). Enters wrist via Guyons canal. Then hand.
ulnar nerve branches and innervation
Articular branches - elbow joint
Muscular branches - in prox forearm. Motor to FCU and medial half of Flex Dig Profundus
Palmar cutaneous branch - mid forearm, prox to wrist. Skin at medial palm overlaying medial carpal bones
Dorsal cutaneous branch - distal forearm, prox to wrist. Deep to FCU and goes to dorsal hand.
Superficial branch of ulnar n
Deep branch of ulnar n
In all, ulnar n supplies motor innervation to FCU, medial half of flex dig profundus and all intrinsic hand muscles other than LOAF muscles (lateral 2 lumbricals, opponens pollicis, abductor pollicis brevis, flexor pollicis brevis).
Sensory to skin of palmar and dorsal aspects of medial 1.5 digits and adjacent palm. Skin on medial side of dorsal hand.
Musculocutaneous nerve course
Comes from lateral cord BP at the inferior border of pec minor. The first muscle it enters is coracbrachialis and gives branches to this muscle before entering it. Then it runs in flexor compartment superficial to brachialis but deep to biceps. As it descends it innervates both of those muscles.
After giving small branch to humerus and articular branches to elbow it pierces deep fascia and emerges lateral to biceps. It continues as the lateral cutaneous nerve of forearm.
it terminates as lateral cutaneous nerve of forearm that supplies anterolateral skin of forearm.
Inntervation - coracobrachialis, biceps brachii, brachialis
Median Nerve course
After its formation from the brachial plexus the median nerve descends down the center of the arm in a superficial course. It starts out lateral to brachial artery but as it descends it becomes medial
Just before it enters the forearm, the median nerve passes btw tendons of biceps and brachialis. It then AGAIN becomes lateral to brachial artery.
Next, to get to the forearm it passes between the deep and superficial heads of pronator teres. Once it passes that point it dives deeper and runs between flexor dig profundus and flexor dig superficialis
Median nerve then passes through carpal tunnel beneath flexor retinaculum and terminates by dividing into 2 terminal branches - common palmar digital nerves
Median nerve innervation summary
Motor - Flexor muscles in forearm (not FCU and ulnar head of flex dig prof though), muscles of thenar eminence, radial 2 lumbricals
Sensory - Skin of palmar and distal dorsal aspects of lateral 3.5 digits and palm. Palmar and distal dorsal aspects of thumb and radial half 2nd digit. Palmar and distal dorsal aspects of adj sides of 2nd-4th digits. Central palm.
