Study note
AnatomyAxilla

Brachial plexus roots and segmental variations

THE CONTEXT
The segmental origin of the brachial plexus may shift upward or downward, producing named variants.

Root contributions

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The roots are the anterior primary rami of C5–C8 and T1, with contributions from C4 and T2.

Prefixed and postfixed plexuses

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An upward shift of the plexus origin by one segment produces a prefixed plexus; a downward shift produces a postfixed plexus.
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In a prefixed plexus, the C4 contribution is large and the T2 contribution is often absent.
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