Brachial plexus

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The brachial plexus (Latin name "Plexus brachialis") is an arrangement of nerve fibres (a plexus) running from the spine (vertebrae C5-T1), through the neck, the axilla (armpit region), and into the arm. All nerves of the arm stem form the brachial plexus (with the exception of the intercostobrachialis nerve which supplies an area of skin near the axilla). Therefore, lesions of the plexus can lead to severe functional impairment.

Anatomy

The brachial plexus starts from the five ventral rami of the spinal nerves, after they have given off their segmental supply to the muscles of the neck. These are the five roots.

These roots merge to form three trunks: "superior" or "upper" C5-C6, "middle" C7, and "inferior" or "lower" C8-T1.

Each trunk then splits to form an anterior and a posterior division.

These six divisions will regroup to become the cords. The cords are named by their position in respect to the axillary artery.

• The posterior cord is formed from the three posterior divisions of the trunks.
• The lateral cord is the anterior divisions from the upper and middle trunks.
• The medial cord is simply a continuation of the lower trunk.

Branches of the brachial plexus

Three branches from the roots

1. Dorsal scapular nerve
2. * arises from C5 root, supplies the rhomboid muscles and levator scapulae.
3. Nerve to subclavius
4. * arises from C5 and C6 roots, supplies the subclavius muscle
5. Long thoracic nerve
6. * arises from C5, C6 and C7 roots, supplies serratus anterior

One branch from the trunks

1. Suprascapular nerve
2. * arises from the superior trunk, supplies supraspinatus and infraspinatus muscles

Three branches from the lateral cord

1. Lateral pectoral nerve
2. * supplies pectoralis major and pectoralis minor( by communicating with the medial pectoral nerve) from C5, C6, C7.
3. Musculocutaneous nerve
4. * from C5 and C6 it supplies coracobrachialis, brachialis and biceps brachii. It then becomes the lateral cutaneous nerve of the forearm.
5. Lateral root of the median nerve
6. * supplies C5, C6 and C7 fibres to the median nerve.

Five branches from the posterior cord

1. Upper subscapular nerve
2. * supplies subscapularis (upper part) from C5 and C6
3. Thoracodorsal nerve
4. * supplies latissimus dorsi with nerve fibres from C6, C7 and C8
5. Lower subscapular nerve
6. * supplies the lower part of subscapularis and teres major from C5 and C6.
7. Axillary nerve
8. * from C5 and C6, it supplies deltoid and a small area of overlying skin by its anterior branch.
9. *Its posterior branch supplies teres minor and deltoid muscles then becomes the upper lateral cutaneous nerve of the arm
10. Radial nerve
11. * nerve fibres from all 5 roots (C5-T1)
12. * largest nerve of the plexus
13. * supplies triceps brachii, the skin of the posterior arm as the posterior cutaneous nerve of the arm, anconeus, and the extensor muscles of the forearm.

Five branches from the medial cord

1. medial pectoral nerve
2. * from C8 and T1, it supplies pectoralis major and pectoralis minor
3. medial root of the median nerve
4. * supplies C8 and T1 fibres to the median nerve.
5. medial cutaneous nerve of the arm
6. * supplies the front and medial skin of the arm from C8 and T1
7. medial cutaneous nerve of the forearm
8. * supplies medial skin of the forearm from C8 and T1
9. ulnar nerve
10. * C7, C8 and T1 fibres
11. * supplies flexor carpi ulnaris, the medial 2 bellies of flexor digitorum profundus, most of the small muscles of the hand and the skin of the medial side of the hand and medial one and a half fingers.

Anesthesia of the Brachial Plexus

The fact that the nerves of the brachial plexus are grouped together acts as a benefit as well. Local anesthetics such as lidocaine or bupivacaine can be injected in close proximity to these nerves, rendering an entire arm insensate and immobile. The process of injecting local anesthetic for this purpose is called regional nerve blockade or more simply, a nerve block, and it is a common procedure in anesthesia. After an onset time of approximately 10 to 15 minutes, the targeted arm will be fully anesthetized and ready for surgery. The patient can remain awake during the ensuing surgical procedure, or he can be sedated with medications or fully anesthetized with general anesthesia as the situation requires.

Peripheral nerve blockade

The use of peripheral nerve blockade (in this case, a "brachial plexus nerve block") offers several advantages when compared to general anesthesia or local anesthesia:

• The patient can remain awake and breathing on their own, thus protecting themselves from aspiration of stomach contents into the lungs. By avoiding general anesthesia, patients with adverse reactions to general anesthetics (viz. malignant hyperthermia, severe post-operative nausea and vomiting, known hypersensitivity to agents) can be successfully treated. Similarly, patients who experience nuisance side effects from general anesthesia such as nausea, vomiting, or excessive sleepiness can minimize these symptoms.
• There is no need to perform an endotracheal intubation, the procedure of inserting a breathing tube into the trachea. Occasionally, such intubation is unexpectedly difficult to perform, causing injury to the patient.
• The affected limb's sympathetic nerves are anesthetized, leading to vasodilation. This improves blood flow to the affected limb and makes microvascular surgical procedures technically simpler.
• The limb can remain numb for several hours after surgery, providing excellent pain relief.
• Deep and superficial structures of the limb are similarly anesthetized, allowing extensive surgical exploration and correction to occur. This is in contrast to locally injected local anesthetics, which tend only to numb superficial structures in the immediate vicinity of the injection.

Brachial plexus blockade

Brachial plexus blockade is the preferred anesthetic technique when:

• Surgery is expected to be limited either to a region between the midpoint of the humerus and the fingers (in which case the brachial plexus block should be either a supra-clavicular, infra-clavicular, subcoracoid, or axillary block), OR surgery is expected to be limited to a region between the midpoint of the humerus and the shoulder (in which case the brachial plexus block should be an interscalene block). Because of the distribution of the local anesthetics on the various portions of the brachial plexus, surgeries crossing the midpoint of the humerus often reveal patchy, unanesthetized portions of the arm. Such procedures probably should not be performed under regional nerve block alone.

AND

• There are no contra-indications to a block such as infection at the intended injection site, significant anti-coagulation, allergy or hypersensitivity to local anesthetic medications, or disproportionate risk in the event of a local anesthetic toxic reaction (seizure) such as gastric aspiration in a patient who has not adequately fasted,

AND

• There will not be a need to perform a neurologic examination immediately following the surgical procedure,

AND

• Patient prefers this technique over other available and reasonable approaches.

Injuries

Two injuries types are recognised in brachial plexus injuries: Traumautic and Obstetric.

Traumatic injuries often are the result of high velocity RTA's (Road Traffic Injuries). The most common form of injury are the motorcycle drivers falling, with either the head/neck pushed to the side (upper plexus lesions) or with their arm abducted (stretched upwards) which produces a lower plexus injury.

The brachial plexus is susceptible to injuries that produce abduction of the thoracic limb from the body wall or a direct blow to the lateral surface of the scapula.

The cardinal signs of brachial plexus avulsion are:

• a weakness in the arm
• diminished reflexes
• corresponding sensory deficits

The nerve roots are stretched or torn from their origin by this trauma, since the meningeal coverings of the nerve roots are thinner than those in the peripheral nerve. The epineurium of the peripheral nerve is contiguous with the dural mater, providing extra support to the peripheral nerves. In cases where the nerve roots have been torn, recovery is unlikely without new experimental surgical techniques.

The diagnosis may be confirmed by an EMG examination in 5-7 days. The evidence of denervation will be evident. If there is no nerve conduction 72 hours after the injury, then avulsion is most likely.

External links

• [Illustration at Backpain Guide]
• [Overview at washington.edu]
• [Brachial Plexus Illustration, Cincinnati Children's Hospital Medical Center]
• [Tutorial at uvm.edu (requires Shockwave)]

Major nerves (also see Peripheral nervous system)

Cranial nerves: I olfactory | II optic | III oculomotor | IV trochlear | V trigeminal | V1 ophthalmic (lacrimal, frontal, supratrochlear, supraorbital, nasociliary, ciliary ganglion) | V2 maxillary (sphenopalatine ganglion) | V3 mandibular (buccal - auriculotemporal - lingual - inferior alveolar - otic ganglion) | VI abducens | VII facial (chorda tympani, nervus intermedius) | VIII vestibulocochlear (cochlear, vestibular) | IX glossopharyngeal | X vagus (recurrent laryngeal, Alderman's nerve) | XI accessory | XII hypoglossal Posterior spinal nerves: greater occipital C1-C4 - Cervical plexus: lesser occipital | greater auricular | lesser auricular | phrenic | ansa cervicalis C5-C8, T1 - Brachial plexus: supraclavicular branches (dorsal scapular, suprascapular, long thoracic) | lateral cord (musculocutaneous, lateral antibrachial cutaneous, lateral head of median nerve) | medial cord (ulnar, medial head of median nerve, medial antibrachial cutaneous, medial brachial cutaneous) | posterior cord (axillary, radial) T2-T11: intercostal T12, L1-L5 - Lumbar plexus: iliohypogastric | ilioinguinal | genitofemoral | lateral femoral cutaneous | femoral | obturator S1-S4 - Sacral plexus: gluteal | posterior femoral cutaneous | tibial | sciatic | sural | common peroneal S2-S5 - Pudendal plexus: perforating cutaneous | pudendal | visceral | muscular | anococcygeal

 

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