Upper Extremity PNS Flashcards
Median Nerve
- Formed by lateral (C6/7) and medial cords (C8/T1) of the brachial plexus
- Runs medial to axillary artery - > medial epicondyle of humerus.
- May be entrapped at Ligament of Struthers (ligament from spur on medial humerus to medial epicondyle in 1% of population). Affects all median muscles.
- In antecubital fossa, runs adjacent to brachial artery - > under Lacertus Fibrosus (band from biceps tendon to ulna)
- First supplies Pronator Teres then runs between two heads of this muscle
- Next, supplies FCR, FDS, and PL (some people)
- Then gives off pure motor AIN approximately 5-8 cm distal to medial epicondyle which supplies FPL, FDP (1,2), PQ)
- After giving off AIN, it passes deep to FDS (Sublimis Bridge) then giving off palmar cutaneous sensory branch to the thenar eminence just proximal to the carpal tunnel.
- Passes through the carpal tunnel along with FDP, FDS, and FPL tendons.
- Divides into motor and sensory branches in the palm. Motor branch divides with the recurrent thenar motor supplying the thumb muscles and other branch supplying first and second lumbricals (LOAF muscles (Lumbricles (1,2), OP, AbdPB, FPB (superficial head))
- Muscles Innervated: pronator teres, flexor carpi radialis, FDS, palmaris longus (some)- > AIN (FPL, FDP (1,2), PQ) -> LOAF muscles (Lumbricles (1,2), OP, AbdPB, FPB (superficial head))
Ulnar Nerve Course
- Terminal extension of the medial cord supplied by lower trunk of the brachial plexus (C8-T1)
- Descends along the medial arm before passing through the Arcade of Struthers composed of fascia from the brachialis to the medial head of triceps
- Passes through Ulnar Groove before passing under the arch of the two heads of the FCU (Humeral-Ulnar aponeurosis) = Cubital Tunnel
- After passing through the cubital tunnel, branches to the FCU and FDP (3,4) are given off.
- Dorsal ulnar cutaneous branch is given off 5 – 8 cm proximal to the wrist
- Palmar cutaneous sensory branch given off at level of ulnar styloid
- Nerve passes into Guyon’s canal at level of the wrist crease
- In the canal, nerve divides into deep palmar motor and superficial sensory branch (sensory to volar 4th/5th and motor to palmaris brevis)
- Deep motor continues to give off the hypothenar motor (ADM, FDM, ODM) before passing under the pisohamate hiatus
- After passing under the hiatus, deep motor supplies lumbricals (3,4), dorsal interossei (4), palmar interossei (3), adductor pollicis, and flexor pollicis brevis (deep head)
Guyon’s Canal Classification
- Type I: Deep Motor and Superficial Sensory
- Type II: Deep Palmar Motor Branch Only
- Type III: Superficial Sensory Branch Only
Ulnar Sensory to the Hand
- dorsal ulnar cutaneous given off 5-8 cm proximal to the wrist
- palmar cuteaneous given off at level of ulnar styloid
- superfical sensory given off in Guyon’s canal
Radial Nerve
- Arises from posterior cord receiving innervation from C5-T1 nerve roots
- First gives off posterior cutaneous nerve of the arm, lower lateral cutaneous nerve of the arm, and posterior cutaneous nerve of the forearm
- Next gives branches to three heads of the triceps and the anconeus
- Then, wraps around the Spiral Groove and descends in the elbow to supply the brachioradialis and ECRL
- 3-4 cm distal to the lateral epicondyle, the nerve splits into superficial radial sensory and deep radial motor branch
- Deep radial motor branch innervates the ECRB and Supinator before entering the Arcade of Froshe (proximal border of the supinator)
- After entering the Arcade, nerve becomes the PIN and supplies rest of the radial muscles in the arm and hand – Extensor digitorum communis, Extensor digiti quinti, Extensor carpi ulnaris, Abductor pollicis longus, Extensor pollicis longus, Extensor pollicis brevis, Extensor indicis proprius
Brachial Plexus Path
- Ventral rami exit between anterior and middle scalene muscles
- Divides into divisions at the clavicle
- Plexopathy 2/2 to cancer, traction, TOS, neuralgic amyotrophy
Upper Trunk Plexopathy
- Weakness of nearly all C5-C6 muscles with lateral sensory loss
- Most affected is deltoid, biceps, brachioradialis, supraspinatus, infraspinatus
- Decreased or absent biceps and brachioradialis reflexes
- Lesion results in Erb’s palsy or “Waiter’s tip” position. Wrist flexed 2/2 to ECR longus weakness.
- Radiation usually affects upper trunk (myokymic discharges)
Lower Trunk Plexopathy
- Involves all ulnar muscles, radial C8 muscles (EIP, EPB), and median C8-T1 muscles (spares PT, FCR, PL)
- Medial sensory loss
- C8 and T1 are most common sites of nerve root avulsions due to less protection
- Tumors usually affect lower trunk
Middle Trunk Plexopathy
- Rare and mimics C7 radiculopathy
- Weakness primarily of triceps, FCR, and pronator teres.
- Sensory loss of middle finger and posterior cutaneous of forearm
Lateral Cord Plexopathy
Involves musculocutaneous nerve, C6-C7 of median nerve, and LAC
Medial Cord Plexopathy
Identical to Lower trunk Plexopathy except intact radial C8 fibers.
Posterior Cord Plexopathy
- Involves radial, axillary, and thoracodorsal nerves
- Sensory loss of lateral arm and posterior arm, posterior forearm, and radial dorsal hand
Dorsal Scapular innervation source
Arises directly from C4 and C5 roots directly
Long Thoracic Innervation Source
Arises from C5 – C7 roots directly
Draw the Brachial Plexus
List branches of brachial plexus (lateral to medial) and muscles innervated.
Lacertus Fibrosus
proximal median nerve entrapment site composed of a band from biceps tendon to ulna. Can affect all median muscles.
Arcade of Struthers
Ulnar nerve entrapment site before the ulnar groove that is composed of fascia from the brachialis to the medial head of triceps. Entrapment may affect all ulnar nerve muscles.
Cubital tunnel
arch of the two heads of the FCU (Humeral-Ulnar aponeurosis) where ulnar nerve passes after ulnar groove. FCU may or may not be involved.
Arcade of Froshe
- proximal border of Supinator where radial nerve passes after supplying ECRB and Supinator
- with posterior interosseous neuropathy at this site, patient may be able to weakly extend wrist with radial deviation (ECRB, ECRL intact)
- supinator may be spared
Musculocutaneous nerve course
- extension of lateral cord
- pierces and supplies coracobrachilis distal to coracoid
- runs between biceps and brachialis in anterior compartment to arm
- supplies biceps and brachialis
- pierces deep fascia lateral to biceps tendon and becomes the lateral antebrachial cutaneous nerve
Thoracic outlet syndrome
fibrous band from cervical rib to first thoracic rib traps the lower trunk of the brachial plexus
How can you differentiate between pronator teres syndrome vs lacertus fibrosus entrapment?
pronator teres is usually spared with pronator teres syndrome
Impingment at what site affects the infraspinatus but spare the supraspinatus?
spinoglenoid notch
What nerve is most commonly affected in neuralgic amyotrophy?
Suprascapular
