Brachial Plexus and Arm Nerves

Brachial Plexus

• Originates from the intervertebral foramen
• Nerve roots include C5-T1
• Lies between the anterior and middle scalenes
• It's inferior to the clavicle, superficially located to the first rib
• Runs deep to the pectoralis minor, anterior to the coracoid process
• Situated along the lateral border of the pectoralis minor

MARMU

• An acronym
• Stands for Musculocutaneous, Axillary, Radial, Median, and Ulnar nerves

Musculocutaneous Nerve (C5-C7, supine position)

• Pierces through the coracobrachialis muscle
• Runs deep to the biceps brachii
• Located superficially to the brachialis muscle
• Found lateral to the biceps tendon
• Becomes the lateral antebrachial cutaneous branch
• Innervates the skin of the lateral forearm

Axillary Nerve (C5-C6, side-lying position)

• Located under the armpit
• Runs anterior to the subscapularis muscle
• Exits through the quadrangular space, which includes the teres minor/major, humerus, and the long head of the triceps
• Wraps around the surgical neck of the humerus
• Innervates the skin of the lateral upper to mid-arm
• Innervates the deltoid and teres minor muscles

Radial Nerve (C5-T1, side-lying position)

• Located under the armpit
• Exits through the triangular space, formed by the triceps long head, teres major, and humerus
• Runs along the posterior arm via the spiral/radial groove from medial to lateral
• Pierces the lateral intermuscular septum
• Situated between the brachialis and brachioradialis muscles at the cubital fossa
• Found anterior to the lateral epicondyle of the humerus
• Divides into two branches

Radial Nerve - Superficial Branch

• Runs deep to the brachioradialis muscle
• Crosses the anatomical snuff box distally and is purely sensory
• Innervates the skin on the radial side of the hand

Radial Nerve - Deep Branch

• Pierces through the supinator muscle
• Travels posterior to the forearm
• Innervates the forearm extensor muscles

Median Nerve (C5-T1, supine position)

• Located on the medial side of the arm
• Travels along the brachial artery
• Passes under the bicipital aponeurosis into the cubital fossa
• Pierces through the two heads of the pronator teres muscle
• Runs deep to the flexor digitorum superficialis
• Located superficially to the flexor digitorum profundus
• Runs deep to the carpal tunnel
• Passes under the flexor retinaculum sheath
• Innervates the skin on the finger side of the first, second, and third fingers and wraps around the nails
• Innervates the thenar eminence and some forearm flexor muscles

Ulnar Nerve (C8-T1, supine position)

• Located on the medial side of the arm
• Runs through the medial intermuscular septum
• Posterior to the medial epicondyle of the humerus
• Travels through the groove for the ulnar nerve
• Pierces through the two heads of the flexor carpi ulnaris muscle
• Runs through Guyon's canal (pisiform and hook of hamate)
• Innervates the skin of the fourth and fifth fingers
• Innervates the hypothenar muscles and the flexor carpi ulnaris

Upper Limb Tension Test 1 (ULTT 1) for Median Nerve

• Patient position is supine
• Depress the shoulder
• Abduct the glenohumeral joint to 110 degrees
• Flex the elbow to 90 degrees
• Fully extend the wrist and elbow

Upper Limb Tension Test 2 (ULTT 2) for Median, Axillary, and Musculocutaneous Nerves

• Patient position is supine
• Depress the shoulder with hip
• Abduct the glenohumeral joint to 10 degrees
• Flex the elbow to 90 degrees
• Supinate the forearm
• Extend the elbow and wrist

Upper Limb Tension Test 3 (ULTT 3) for Radial Nerve

• Patient position is supine
• Depress shoulder with hip
• Adduct the glenohumeral joint to 10 degrees
• Flex elbow to 90 degrees
• Pronate the forearm
• Flex wrist, extend elbow

Upper Limb Tension Test 4 (ULTT 4) for Ulnar Nerve

• Patient position is supine
• Depress the shoulder
• Abduct the glenohumeral joint to 90 degrees
• Flex the elbow to 90 degrees
• Pronate the arm
• Fully extend the wrist
• Laterally rotate the shoulder
• Flex elbow bringing fingers towards head

Erb's Palsy

• Affects the C5 and C6 nerve roots of the brachial plexus
• Is often caused by trauma during childbirth
• Causes persistent elbow extension
• It is also known as Waiter's Tip Syndrome
• Affects the axillary nerve, biceps, and brachialis muscles

Horner Syndrome

• Also known as oculosympathetic palsy, affects one side of the face
• Results from damage to the sympathetic nerves connecting the brainstem to the eyes and face
• Ptosis involves drooping of the upper eyelid
• Miosis is constriction of the pupil, leading to mismatched pupil sizes
• Anhidrosis involves decreased or absent sweating on the affected side of the face
• Enophthalmos involves the appearance of a sunken eyeball (not always present)
• Causes include carotid artery dissection, apical lung tumor, middle ear infection, and birth trauma in congenital cases

Wrist Drop

• Inability to extend the hand

Radial Nerve Palsy

• Als known as Crutch Palsy, Saturday Night Palsy, or Honeymooners Palsy
• Prolonged compression of the radial nerve can result where it is near or at the axillary level
• The proximal forearm is a compressed site where the posterior interosseous branch of the radial nerve passes between the supinator heads
• Affects the radial nerve

Carpal Tunnel Syndrome

• Overuse of tendons leads to inflammation causing compression of the median nerve, causing significant pain and weakness
• The pain will be present in the first three and a half digits and is worse at night
• Weakness is usually present in the thenar eminence if severe
• Lifestyle risks include repetitive tasks like typing, computer work, writing, weight gain, pregnancy, and overuse
• Predisposing factors are hypothyroidism, diabetes, arthritis, or previous injury
• Affects the median nerve

Pronator Syndrome

• Median nerve compression injury
• Pain localized to the anterior proximal forearm due to compression of the nerve by muscle bellies of the pronator teres
• Paresthesia in the distribution of the median nerve
• Numbness over the palm
• Risk factors are similar to those of carpal tunnel (repetitive tasks)
• Affects the median nerve

Ape Hand

• Loss of thumb innervation
• Loss of muscle mass of the thumb
• Affects the median nerve

Injection Nerve Palsy

• Iatrogenic condition caused by intramuscular injections proximity to a nerve.
• Leads to axonal and myelin degeneration.
• The agent penetrates the endoneurium, causing edema, nerve damage, and nerve death.
• Is extremely painful and motor function is severely affected
• Affects the median nerve

Anterior Interosseous Syndrome

• Palsy of flexor pollicis longus, the index and long fingers of the flexor digitorum profundus, pronator quadratus
• Pain in the forearm, weakness of index and thumb finger pincer movement
• Can be spontaneous or traumatic
• Traumatic causes include forearm fractures, penetrating injuries, stab wounds, cast fixation, venipuncture, and complications from internal fixations
• Spontaneous factors can include brachial plexus neuritis, compartment syndrome, and compression neuropathy
• It affects the median nerve

Klumpke Palsy

• Lower trunk injury to the brachial plexus
• Hyper abduction traction

Klumpke Palsy - Effects

• Decreased sensation along the medial aspect of the distal upper extremity with C8 and T1 involvement
• neurological damage leads to muscular atrophy and tightening, presenting as a "claw hand"
• Lower trunk injuries typically result from upward force on an infant's arm or upward traction on an adult's arm
• Injuries occur from traumatic vaginal delivery with traction of an abducted arm
• Affects the ulnar nerve

Cubital Tunnel Syndrome

• Causes ulnar entrapment in the cubital tunnel
• Composed of Osbourne's ligament (cubital tunnel retinaculum) and the deep layer of the aponeurosis of the 2 heads of the flexor carpi ulnaris muscle
• Peripheral neuropathy caused by chronic compression or repetitive trauma of the ulnar nerve at the elbow
• Affects the ulnar nerve

Lumbar Plexus: Obturator Nerve (L2-L4, supine)

• derived from lumbar plexus
• descends inferior to arcuate line
• passes through obturator foramen
• exits into medial thigh, innervating cutaneous patch of distal medial thigh
• innervates adductor muscles

Lumbar Plexus: Femoral Nerve (L2-L4, supine)

• the origin is the lumbar plexus
• exits between psoas and iliacus
• runs towards the inguinal ligament
• travels with an artery and vein
• Muscles innervated are the quads, sartorius, psoas, and sometimes pectineus
• cutaneous branch turns known as the saphenous nerve at medial thigh
• innervates medial side of leg to medial malleolus

Sciatic Nerve: Lumbosacral Trunk (S1-S2, prone)

• derived from the sacral plexus
• travels through greater sciatic notch
• Located below piriformis and above glator mm (superior gemellus, obturator internus, inferior gemellus, obturator extended, and rec fem
• Is deep to the biceps femoris beside adductor magnus
• Ends at the popliteal fossa then divides into two branches

Tibial Nerve : (Prone)

• Arises from the sciatic nerve in the distal thigh, at the popliteal fossa
• Runs deep to posterior leg
• Passes through the popliteal fossa and deep to the gastrocnemius
• Innervates the superficial posterior compartment
• Provides sensory and motor function to most of the posterior leg and foot
• The Deep posterior compartment travels in the tibial nerve
• Travels posterior to the medial malleolus
• Splits into medial and lateral plantar nerves, innervating the plantar skin and muscles

Common Fibular Nerve -

• Prone comes from the sciatic nerve from the popliteal fossa
• Runs lateral and inferior to head of fibula
• Pierces through fibularis longus
• Then divides into deep and superficial nerves

Superficial Fibular Nerve

• Prone wraps around the neck of the fibula
• Runs in the lateral compartment of the leg
• Passes between fibularis muscles and the lateral side of the extensor digitorum longus
• Innervates the skin of anterolateral distal 1/3 of leg and dorsum of foot except for webspace between hallux and second digit
• nnervates fibularis longus and brevis

Deep Fibular Nerve

• Prone between fibula and upper part of fibularis longus
• Runs in the anterior compartment of leg
• Passes deep to EDL along the anterior surface of the interosseous membrane
• Runs laterally to the anterior tibial artery
• Innervates webspace between the first and second toe and innervates EFB and EB

Problems: Tibial Nerve

• Results from direct trauma or peripheral neuropathy, leading to:
  • loss of ankle and toe plantarflexion
  • weakened foot inversion
  • sensory loss to plantar aspect of foot

Injury to Superficial Fibular Nerve

• Superficial peroneal nerve entrapment mechanism:
• ankle sprains and ankle twisting (stretching of superficial peroneal nerve)
• the entrapment when exiting the deep fascia of the leg
• Presents as: pain and paresthesia over of foot
• Factors, proximal fibula fracture perforating injury to lateral leg
• Presents as: loss of eversion motor to peroneus longus and brevis injured sensation loss over distal most skin

Problems: Deep Fibular Nerve caused by:

• systemic, lower-motor neuron disease, diabetes, ishemeia and inflammatory conditions
• latrogenic TKA, surgical injury
• traumatic injury, medical examination
• damage results in foot drop

Problems: Femoral Nerve Trauma

Causes:

• direct trauma, or from medical examination
• tumor compressed or a hematoma
• Clinical - quadriceps waste, loss of knee extension
• Loss of sensation to anterior and medial nerves in thigh

Problems: Tarsal Tunnel Syndrome

• It is also known that tibial nerve dysfunction or "posterior tibial nerve neuralgia."
• It has an entrapment neuropathy.
• CTS is related counterpart counterpart