Human Anatomy
Axilla and Brachial Plexus
Brachial plexus and axilla for MBBS: roots to branches, Erb's and Klumpke's palsy, axillary nerve and artery, and lymph nodes, mapped to NMC codes AN10.1 to AN10.13.
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Axilla and Brachial Plexus
Brachial plexus and axilla for MBBS: roots to branches, Erb's and Klumpke's palsy, axillary nerve and artery, and lymph nodes, mapped to NMC codes AN10.1 to AN10.13.
The axilla and brachial plexus chapter is where upper-limb neurology is set for the rest of the course. It covers the formation and branches of the plexus, the axillary artery and its parts, the contents of the axilla, and the classic nerve-injury patterns that examiners return to again and again.
High-yield: Axilla and Brachial Plexus
- The brachial plexus is formed by the ventral rami of C5 to T1.
- Its parts, from proximal to distal, are roots, trunks, divisions, cords and branches.
- The three trunks are upper (C5 to C6), middle (C7) and lower (C8 to T1), lying in the posterior triangle of the neck.
- The cords are named lateral, medial and posterior by their relation to the second part of the axillary artery.
- Erb's palsy injures the upper trunk (C5 to C6) and gives the waiter's tip position: arm adducted, medially rotated, forearm pronated.
- Klumpke's palsy injures the lower trunk (C8 to T1), giving a claw hand and sometimes Horner's syndrome.
- The long thoracic nerve (C5 to C7) supplies serratus anterior; injury causes winging of the scapula.
- The axillary nerve winds round the surgical neck of the humerus; injury paralyses deltoid and numbs the regimental badge area.
- The radial nerve runs in the spiral groove; a midshaft humeral fracture causes wrist drop.
- The musculocutaneous nerve pierces coracobrachialis and supplies the flexor compartment of the arm.
- The axillary artery is divided into three parts by pectoralis minor.
- The posterior cord gives the axillary and radial nerves; the medial cord gives the ulnar nerve and the medial root of the median nerve.
- The axilla contains the axillary vessels, the cords and branches of the plexus, and the axillary lymph nodes.
- Axillary lymph nodes drain the upper limb, the chest wall and most of the breast, which is why they are central to breast cancer staging.
Classic nerve injuries
- **Erb's palsy (C5 to C6):** Upper trunk. Waiter's tip position. From excessive traction on the neck, as in a difficult delivery.
- **Klumpke's palsy (C8 to T1):** Lower trunk. Claw hand, may cause Horner's syndrome.
- **Axillary nerve:** Surgical neck of humerus. Deltoid paralysis, regimental badge sensory loss.
- **Radial nerve:** Spiral groove of humerus. Wrist drop.
- **Long thoracic nerve:** Serratus anterior. Winging of the scapula.
NMC competencies in this chapter
- **AN10.1:** Boundaries and contents of the axilla
- **AN10.5:** Formation, parts and branches of the brachial plexus
- **AN10.8:** Effects of brachial plexus injuries, Erb's and Klumpke's palsy
- **AN10.9:** Axillary artery: parts, branches and anastomoses around the scapula
- **AN10.11:** Axillary lymph nodes and their clinical importance
- **AN10.13:** Nerve injuries around the shoulder and their motor and sensory loss
Frequently Asked Questions
What is the difference between Erb's and Klumpke's palsy?
Erb's palsy injures the upper trunk (C5 to C6) and gives the waiter's tip position. Klumpke's palsy injures the lower trunk (C8 to T1) and gives a claw hand, sometimes with Horner's syndrome.
Why is winging of the scapula important?
It signals long thoracic nerve injury with serratus anterior paralysis, which can follow axillary surgery or trauma and is a common examination and exam finding.
Why are axillary lymph nodes central to breast cancer?
They drain most of the breast, so their involvement is a key part of staging and management of breast carcinoma.
How is the axillary artery divided?
Pectoralis minor divides it into three parts, a favourite anatomical landmark for locating the cords of the brachial plexus.
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