Brachial Plexus

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Introduction

The Brachial Plexus is 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).

The right brachial plexus with its short branches, viewed from in front.

Function

The brachial plexus 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.

Description

Path

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 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 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)

Anatomical illustration of the brachial plexus with areas of roots, trunks, divisions, and cords marked.

Specific Branches

The branches are listed below. They mostly branch from the cords, but some originate from earlier structures (indicated in italics).

Bold indicates primary spinal root component of the nerve. Italics indicate spinal roots that frequently, but not always, contribute to the nerve.

From	Nerve	Roots	Muscles	Cutaneous
roots	Dorsal scapular nerve	C4, C5	Rhomboid muscles and Levator scapulae	-
roots	Long thoracic nerve	C5, C6, C7	Serratus anterior	-
upper trunk	Nerve to the subclavius	C5, 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 (by communicating with the Medial pectoral nerve)	-
lateral cord	Musculocutaneous nerve	C5, C6, C7	Coracobrachialis, Brachialis and Biceps brachii	becomes the Lateral cutaneous nerve of the forearm
lateral cord	lateral root of the Median nerve	C6, C7	fibres to the median nerve	-
posterior cord	Upper subscapular nerve	C5, C6	Subscapularis (upper part)	-
posterior cord	Thoracodorsal nerve (middle subscapular nerve)	C6, C7, C8	Latissimus dorsi	-
posterior cord	Lower subscapular nerve	C5, C6	subscapularis (lower part ) and Teres major	-
posterior cord	Axillary nerve	C5, C6	anterior branch: deltoid and a small area of overlying skin posterior branch: Teres minor and deltoid muscles	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	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, T1	fibres to the median nerve	portions of hand not served by ulnar or radial
medial cord	Medial cutaneous nerve of the arm	C8, T1	-	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

Specific branches can be visualised on the diagram below:

Injuries

Injury to the brachial plexus can be very problematic because the nerves branching off of the plexus provide innervation to the upper extremity. Clinical signs and symptoms vary with which area of the plexus is involved, and generally result in paralysis or anesthesia.

Symptoms can range from transient nerve dysfunction to complete upper extremity weakness. Because of the anatomical variants of the brachial plexus these injuries can be a challenge to diagnose.

Mechanism of Injury

The main causes of brachial plexus palsies are traction, due to 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. The rare Parsonage-Turner Syndromecauses brachial plexus inflammation without obvious injury, but with nevertheless disabling symptoms. But in general, brachial plexus lesions can be classified as either traumatic or obstetric.

• Obstetric injuries may occur from a mechanical injury involving shoulder dystocia during a difficult childbirth. During birth, excessive stretching of the neck or pulling the upper extremity 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 penetrating or sports-related injuries, falls, work-related injuries, radiation therapy and iatrogenic causes (i.e. first rib resection, shoulder surgery, brachial plexus block). However, the most common mechanism of injury is a traction injury due to the forceful separation of the neck from the shoulder.

Common associated injuries can include fractures of the proximal humerus, clavicle, scapula, cervical spine and upper limb vascular injuries. Management of these injuries may complicate the picture when diagnosing brachial plexus injury but can also guide in determining the mechanism of injury.

Classification of Injury

There are many classification systems for brachial plexus injuries, they can be divided into three types:

1. An upper brachial plexus lesion, which occurs from excessive lateral neck flexion away from the shoulder. Most commonly, forceps delivery or falling on the neck at an angle causes upper plexus lesions leading to Erb's Palsy. This type of injury 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.
2. Less frequently, the whole brachial plexus lesion occurs.
3. Most infrequently, sudden upward pulling on an abducted arm (as when someone breaks a fall by grasping a tree branch) produces a lower brachial plexus lesion, in which the eighth cervical (C8) and first thoracic (T1) nerves are injured either before or after they have joined to form the lower trunk. The subsequent paralysis affects the intrinsic muscles of the hand and the flexors of the wrist and fingers.This results in a form of paralysis known as Klumpke's Paralysis.

However, a commonly used one is Leffert's classification system which is based on etiology and level of injury:

• I Open (usually from stabbing)
• II Closed (usually from a motorcycle accident)
• IIa Supraclavicular (preganglionic or postganglionic)
• IIb Infraclavicular
• IIc Combined
• III Radiation-induced
• IV Obstetric
• IVa Erb's (upper root)
• IVb Klumpke (lower root)
• IVc Mixed

Signs and Symptoms

Nerve damage causes a multifaceted clinical picture consisting of sensorimotor disturbances (pain, muscle atrophy, muscle weakness, secondary deformities) as well as the reorganisation of the Central Nervous System that may be associated with upper limb underuse.

• Pain is most common, in particular, those affecting the preganglionic fibres. Often described as crushing with intermittent severe attacks shooting down the arm.
• Paralysis and anaesthesiain affected extremity.
• Bizarre sensations, hyperalgesia, dysesthesia, and allodynia.
• Myoclonic jerks in the affected extremity.
• Ipsilateral Horners Syndromewith T1 injury.

Investigations

• Xray of the shoulder area and cervical spine to determine if any boney abnormalities are causing the lesion.
• MRI will help to visualise causative pathology such as tumors, neuritis, radiation injury.
• EMG and NCS help to confirm a diagnosis, localise the lesion and determine the degree of axonal loss. These tests are the most useful tests to determine localisation of the plexopathy, especially, the sensory nerve conduction studies (SCSs) because sensory nerve action potential amplitude will decrease in plexopathies due to Wallerian degeneration of the postganglionic sensory fibers.
• Histamine test to differentiate between pre and postganglionic lesion.

Management

brachial plexus injury may result in severe and chronic impairments in both adults and children, thus requiring early and long-lasting treatment.

Medical Management

• The main aspect of medical management is pain control. Often treated in a similar way to neuropathic pain with NSAID, tricyclic antidepressants, anticonvulsants, and oral or transdermal opioids.

Psychological Management

• Psychological problems and a lack of cooperation by the patient may limit rehabilitation effects and increase disability.

Physiotherapy Management (see also Brachial Pluxus Injury for Physiotherapy Management)

The aim is to maintain the range of motion of the extremity, to strengthen the remaining functional muscles, to protect the denervated dermatomes, and to manage pain.

• Pain control - acupuncture, TENS
• Maintaining ROM - passive movements,exercise therapy, splinting, positioning
• Strengthen affected muscles - biofeedback, exercise therapy
• Managing chronic oedema - compression garments, advice, massage therapy

Intervention Management

• Continuous brachial plexus block
• Transcutaneous nerve stimulation
• Dorsal route entry zone (DREZ) ablation or implantable dorsal route stimulators.
• Surgical techniques include neurolysis, nerve grafting, and nerve transfer. Intercostal nerves are commonly used to reinnervate muscles after a brachial plexus injury with avulsion of spinal nerve roots.

Brachial Plexus Block

A brachial plexus block allows a surgeon to operate on an upper extremity without the use of a general anesthetic, when combined with a tourniquet.

The location of the injection is between the posterior border of the sternocleidomastoid and the clavicle. The axillary sheath surrounds the axillary vein, axillary artery, and three cords of the brachial plexus. When the injection takes effect, the muscles and skin innervated by the cords found in the sheath are anesthetized.

Read more here

Other Information

Some mnemonics for remembering the branches:

• Posterior Cord Branches
  • STAR - subscapular (upper and lower), thoracodorsal, axillary, radial
  • ULTRA - upper subscapular, lower subscapular, thoracodorsal, radial, axillary
• Lateral Cord Branches
  • LLM "Lucy Loves Me" - the lateral pectoral, lateral root of the median nerve, musculocutaneous
• Medial Cord Branches
  • MMMUM "Most Medical Men Use Morphine" - medial pectoral, medial cutaneous nerve of arm, medial cutaneous nerve of forearm, ulnar, the medial root of the median nerve

Resources

Journal of Brachial Plexus and Peripheral Nerve Injury

Presentations

Learn the Brachial Plexus in Five Minutes or Less This is a great little presentation to teach you the brachial plexus through simplified drawing. Have a go!

Brachial Plexus Block and Translational Manipulation for Adhesive Capsulitis Created by Tom Denninger & Ben Hando as part of the Evidence in Motion, OMPT Fellowship, 2011 View the presentation

Case Studies

Dahlin LB, Blackman C, Duppe H, Saito H, Chemnitz A, Abul-Kasim K, Maly P. Compression of the lower trunk of the brachial plexus by a cervical rib in two adolescent girls: case reports and surgical treatment. J Brachial Plex Peripher Nerve Inj. 2009;4(14).] - FREE FULL TEXT

Saliba S, Saliba EN, Pugh KF, Chhabra A, Diduch D. Rehabilitation considerations of a brachial plexus injury with complete avulsion of C5 and C6 nerve roots in a college football player: A Case Study. Sports Health. 2009:1(5): 370-375. - FREE FULL TEXT