Upper Extremity - Mononeuropathies & Plexopathies
Upper Extremity - Mononeuropathies & Plexopathies
Major mononeuropathies and plexopathies of the upper extremity
Brachial Plexus
Concise brachial plexus anatomy
- C5 and C6 form the upper trunk.
- C8 and T1 form the lower trunk.
- C7 makes up the middle trunk.
- The posterior divisions of each trunk join to form the posterior cord, which forms the radial nerve, which innervates extensor musculature, and forms the axillary nerve.
- The anterior division of the lower trunk forms the medial cord, which supplies the ulnar nerve; it innervates medial flexors that lie below the elbow.
- The anterior divisions of the upper and middle trunks form the lateral cord, which forms the musculocutaneous nerve.
- In addition to elbow flexion, biceps brachii provides supination, so supination is at least partially preserved in radial nerve injury.
- The branches from the lateral cord and medial cord join to form the median nerve; it innervates lateral flexors that lie below the elbow.
key brachial plexopathies
From superior to inferior:
- Erb's palsy (aka Erb-Duchenne) is an upper trunk plexopathy.
- Klumpke's palsy and thoracic outlet syndrome are lower trunk plexopathies.
- Scapular winging from long thoracic nerve injury/serratus anterior weakness.
- Although this is actually a mononeuropathy, we learn it with the brachial plexopathies, because the long thoracic nerve projects directly from the cervical roots.
Details of key brachial plexopathies
Erb's and Klumpke's palsies:
- Occur from trauma, such as birth trauma from breech birth, high birth weight, or suction.
- Birth trauma more commonly causes an Erb's palsy than a Klumpke's palsy.
- In adults, these occur from most commonly from trauma, such as from breaking a fall.
- Erb's palsy produces a "waiter's tip" deficit, which pictorializes the arm being at the side and pronated – the hand ready to receive the tip!
- Klumpke's palsy produces claw hand wherein the metacarpalphalangeal joints extend and the proximal interphalangeal joints flex, like a claw – it affects both ulnar and distal median nerve musculature, so all fingers are affected!
- Has many causes; we highlight cervical rib and Pancoast tumor as two key compressive causes.
- It produces claw hand like Klumpke's palsy and can also cause vascular compression signs, like edema and arm discoloration, from subclavian artery compression.
- Typically from serratus anterior weakness.
- Has many causes; we highlight trauma, stretch injury, and compression as key causes.
- It produces the characteristic winged scapula, wherein there is prominence of the inferomedial border of the scapula.
upper extremity mononeuropathies
Major bones of the upper extremity.
- Humerus, proximally.
- Radius in the lateral forearm.
- Ulna in the medial forearm.
- Hand bones.
Axillary nerve
Course (in brief)
- Passes posteriorly through the quadrilateral space (aka quadrangular space, lateral axillary hiatus) around the proximal humerus at the surgical neck to innervate the deltoid.
Injury sites
- The axillary nerve can be entrapped in the quadrilateral space along with the posterior circumflex artery or injured in proximal humerus dislocation or fracture (most commonly anterior fracture dislocation of the proximal head of the humerus).
- It manifests, most notably, with weakness of shoulder abduction from deltoid weakness.
Radial nerve
Course (in brief)
- Runs along the posterior upper limb.
- Wraps around the posterior humerus at the mid-shaft, into the forearm where it divides into a lateral (sensory nerve) and a medial (motor nerve).
Injury sites
- The radial nerve can be compressed within the axilla: all of its components are affected here; this commonly occurs from the use of crutches, which compress the nerve.
- Where it wraps around the humerus in the mid-shaft is the spiral groove, an important radial nerve compression site, so called "Saturday night palsy" because it classically develops from hanging an arm on the back of a bar-chair and compressing the nerve (but being unaware of the arm paresthesias because of drunkenness).
- The key way to distinguish these compression sites is that in radial nerve compression within the axilla, the triceps is weak; whereas in spiral groove compression, it is strong because triceps innervation lies proximal to the spiral groove.
- The radial nerve can be compressed when it passes through the supinator muscle in the proximal forearm.
- Radial neuropathy causes extensor muscle weakness with "wrist drop".
Median nerve
Course (in brief)
- The median nerve passes along the medial arm but doesn't innervate any upper arm muscles.
- Within the proximal forearm, the median nerve divides into the anterior interosseous nerve branch and a branch that continues into the hand and provides the recurrent motor branch to the thumb.
Injury sites
- When the distal humerus suffers supracondylar fracture (fracture just proximal to the epicondyles), both the median and ulnar nerves can be injured (more rarely the superficial sensory branch of the radial nerve can be, as well).
- The median nerve can be ensnared in the humeral and ulnar heads of the pronator teres muscle as the median nerve exits the cubital fossa.
- When the anterior interosseous nerve is injured in isolation (anterior interosseous syndrome or neuropathy), patients exhibit the "OK" sign; wherein, they are unable to form a circle with the thumb and index finger. Neither the thumb's interphalangeal joint nor the index finger's distal interphalangeal joints will flex.
- The most common compression site for the median nerve is the carpal tunnel at the wrist: the nerve passes beneath the flexor retinaculum through the carpal tunnel and is compressed.
- The median palmar cutaneous nerve, which enters the hand superficial to the carpal tunnel, so it's spared.
- Laceration of the palm can injure the recurrent branch of the thumb in isolation.
- Median nerve injury produces lateral flexor weakness and thenar eminence (thumb pad) wasting, so-called "ape hand".
Ulnar nerve
Course (in brief)
- Passes medial to the median nerve, then along the medial aspect of the ulna and into the hand.
- Passes posterior to the medial epicondyle of the humerus and through the medial wrist.
Injury sites
- Supracondylar fracture
- Medial epicondyle compression
- Cubital tunnel entrapment (the tendinous arch that joins the heads of flexor carpi ulnaris).
- Guyon's canal (aka Guyon's tunnel) formed from the palmar carpal ligament.
- The vast majority of Guyon canal entrapments only affect the deep, motor branch, which passes between the hook of the hamate and the pisiform bone.
- Fracture of the hook of the hamate can cause ulnar neuropathy.
- Ulnar neuropathy produces weakness of the medial flexors and a more restricted clawing of the hand, so-called ulnar claw, with clawing of digits 4 and 5.
- Whereas Klumpke's palsy affects both median and ulnar nerve distal musculature.
- 4th and 5th digit clawing forms the shape of a Pope's blessing, the so-called: Benediction sign.