The brachial plexus is the complex neural network formed from the ventral rami of C5-T1, organised into roots, trunks (upper C5-6, middle C7, lower C8-T1), divisions, cords (posterior, lateral, medial), and terminal branches. It supplies all motor and sensory function to the upper limb. The plexus passes between the anterior and middle scalenes, beneath the clavicle, and through the axilla to reach the arm.
| Origin | Anterior rami of C5, C6, C7, C8, T1 |
|---|---|
| Course | Roots emerge between scalenus anterior and medius and form upper, middle and lower trunks in the posterior triangle of the neck; each trunk splits into anterior and posterior divisions behind the clavicle, and these form the lateral, medial and posterior cords in the axilla around the axillary artery, ending as the terminal branches |
| Motor |
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| Sensory |
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Brachial plexus injuries range from traction neuropraxia (burner/stinger in contact sports) to complete root avulsion in high-speed trauma. Upper trunk injuries (Erb's palsy, C5-6) produce the waiter's tip posture. Lower trunk injuries (Klumpke's palsy, C8-T1) cause intrinsic hand weakness and Horner syndrome. MRI of the cervical spine and plexus identifies root avulsion from pseudomeningocele formation. Nerve transfer surgery (intercostal to musculocutaneous, accessory to suprascapular) restores function in avulsion injuries. Birth-related brachial plexus palsy from shoulder dystocia recovers spontaneously in 90% of mild cases.
Upper plexus injury (C5,C6) producing shoulder adduction, internal rotation, elbow extension, and forearm pronation, the waiter's tip posture.
Transient plexus stretch in contact sport from neck lateral flexion, causing burning pain and arm weakness lasting seconds to minutes.
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