A network of nerve fibers that run from the spine, passing through the cervico-axillary canal to reach axilla.
It is formed by the ventral rami of the lower four cervical and first thoracic nerve roots (C5-C8, T1).
It is responsible for cutaneous and muscular innervation of the entire upper limb, with two exceptions: the trapezius muscle innervated by the spinal accessory nerve (CN XI) and an area of skin near the axilla innervated by the intercostobrachial nerve.
The brachial plexus is divided into Roots, Trunks, Divisions, Cords, and Branches.
There are five terminal branches and numerous other pre-terminal or collateral branches that leave the plexus at various points along its length.
The five Roots are the five anterior rami of the of the lower four cervical and first thoracic nerve roots (C5-C8, T1), after they have given off their segmental supply to the muscles of the neck.
These Roots merge to form three Trunks:
Upper Trunk (C5-C6)
Middle Trunk (C7)
Lower Trunk (C8, T1)
Each Trunk then splits into anterior and posterior divisions, to form six Divisions.
The anterior/ posterior divisions innervate flexor groups versus extensor groups:
anterior divisions of the upper, middle, and lower trunks
posterior divisions of the upper, middle, and lower trunks
These six Divisions will regroup to become the three Cords.
The Cords are named by their position with respect to the axillary artery.
The Posterior Cord is formed from the three posterior divisions of the trunks (C5-C8,T1)
The Lateral Cord is the anterior divisions from the upper and middle trunks (C5-C7)
The Medial Cord is simply a continuation of the anterior division of the lower trunk (C8,T1)
Specific Branches: Most branch from the cords.
Some branch directly from earlier structures.
These terminal branches are the musculocutaneous nerve, the axillary nerve, the radial nerve, the median nerve, and the ulnar nerve.
roots Dorsal scapular nerve C4, C5 Rhomboid muscles and Levator scapulae
roots Long thoracic nerve C5, C6, C S2242atus anterior upper trunk Nerve to the subclavius rC5, C6 Subclavius muscle upper trunk Suprascapular nerve C5, C6 Supraspinatus and Infraspinatus
lateral cord Lateral pectoral nerve C5, C6, C7 Pectoralis major and Pectoralis minor
lateral cord Musculocutaneous nerve C5, C6, C7 Coracobrachialis, Brachialis and Biceps brachii and becomes the Lateral cutaneous nerve of the forearm
lateral cord lateral root of the Median nerve C6, C7 fibers to the median nerve
posterior cord Upper subscapular nerve C5, C6 Subscapularis (upper part)
posterior cord Thoracodorsal nerve (middle subscapular nerve) C6, C7, C Latissimus dorsi muscle
posterior cord Lower subscapular nerve C5, C6 subscapularis (lower part ) and Teres major muscle
posterior cord Axillary nerve C5, C6 anterior branch: deltoid and a small area of overlying skin
posterior branch: Teres minor and deltoid muscles
The posterior branch becomes Upper lateral cutaneous nerve of the arm
posterior cord radial nerve C5, C6, C7, C8, T1: Triceps brachii, Supinator, Anconeus, the extensor muscles of the Forearm, and Brachioradialis and the skin of the posterior arm as the Posterior cutaneous nerve of the arm
medial cord Medial pectoral nerve C8, T1: Pectoralis major and Pectoralis minor
medial cord medial root of the Median nerve C8, T fibers to the median nerve portions of hand not served by ulnar or radial
medial cord Medial cutaneous nerve of the arm C8, T front and medial skin of the Arm
medial cord Medial cutaneous nerve of the forearm C8, T1 medial skin of the forearm
medial cord Ulnar nerve C8, T1 Flexor carpi ulnaris, the medial two bellies of Flexor digitorum profundus, the intrinsic hand muscles except the Thenar muscles and the two most lateral lumbricals.
the skin of the medial side of the hand and medial one and a half fingers on the palmar side and medial two and a half fingers on the dorsal side
The nerves branching off of the plexus provide innervation to the upper extremity, injuries result in clinical signs and symptoms that vary with which area of the plexus is involved.
Symptoms can range from transient nerve dysfunction to complete upper extremity weakness.
Brachial plexus palsies are due to traction, extreme movements, and heavy impact.
Brachial plexus injury can occur in a variety of ways and can occur as a result of shoulder trauma, tumours, or inflammation.
In general, brachial plexus lesions can be classified as either traumatic or obstetric.
Obstetric injuries may occur from shoulder dystocia during difficult childbirth, with excessive stretching of the neck or pulling the upper extremity during birth, can result in an upper brachial plexus injury or inferior trunk, respectively
The incidence of brachial plexus injury is approximately 1 in 1,000 live births.
Traumatic injury may arise from sports related injuries, falls, work related injuries, radiation therapy and iatrogenic causes such as first rib resection, shoulder surgery, and brachial plexus block.
The most common mechanism of injury is a traction injury due to forceful separation of the neck from the shoulder.
Commonly associated injuries can include: fractures of the proximal humerus, clavicle, scapula, cervical spine and upper limb vascular injuries.
There are many classification systems for brachial plexus injuries, they can be divided into three types:
An upper brachial plexus lesion, which occurs from excessive lateral neck flexion away from the shoulder.
An upper brachial plexus lesion is most commonly due to forceps delivery or falling on the neck at an angle causing upper plexus lesions leading to Erb’s Palsy.
An upper brachial plexus lesion produces a very characteristic sign called Waiter’s tip deformity due to loss of the lateral rotators of the shoulder, arm flexors, and hand extensor muscles.
Less frequently, a whole brachial plexus lesion occurs.
Rarely, sudden upward pulling on an abducted arm, as when someone breaks a fall, produces a lower brachial plexus lesion, in which the eighth cervical (C8) and first thoracic (T1) nerves are injured: subsequent paralysis, Klumpe’s Paralysis, affects, principally, the intrinsic muscles of the hand and the flexors of the wrist and fingers.
Leffert’s classification system of brachial injury based on eitiology and level of injury:
III Radiation induced
IVa Erb’s (upper root)
IVb Klumpke (lower root)
Nerve damage causes sensorimotor disturbances, pain, muscle atrophy, muscle weakness, and secondary deformities, paralysis and anaesthesia in affected extremity. bizarre sensations, hyperalgaesia, dysethesia, allodynia, myoclonic jerks in the affected extremity, ipsilateral Horners Syndrome with T1 injury.
Evaluation includes Xrays of shoulder area and MRI of the cervical spine to determine if any boney abnormalities are causing the lesion.
EMG and NCS can confirm diagnosis, and localize the lesion and determine degree of axonal loss.
Sensory nerve conduction studies (SCSs) are useful because sensory nerve action potential amplitude will decrease in plexopathies due to Wallerian degeneration of the postganglionic sensory fibers.
The main goals of medical management is pain control, and is often treated with NSAIDs, tricyclic antidepressants, anticonvulsants and opioids, and to maintain the range of motion of the extremity, to strengthen the remaining functional muscles, and to protect the denervated dermatomes.
Pain control can be achieved with acupuncture and TENS, brachial plexus block, nerve ablation, dorsal route stimulators and neurolysis.
Physical,therapy with passive movements, exercise therapy to strengthen affected muscles should be employed.
Managing chronic edema with compression garments, and, massage therapy take place.
Intercostal nerves are commonly used to reinnervate muscles after a brachial plexus injury.
A brachial plexus block between the posterior border of the sternocleidomastoid and the clavicle, allows a surgeon to operate on an upper extremity without the use of a general anesthetic.