(Brachial plexus paralysis) A (usually) partial paralysis of the arm due to stretching or tearing of the fibres of the brachial nerve plexus in the armpit. Such damage may occur during birth, especially when the baby is unusually large (See DYSTOCIA). The baby presents with the arm lying by the side of the body with elbow extended, forearm pronated, and the fingers flexed and is unable to raise the arm. Spontaneous recovery occurs in most but microsurgery to reattach the nerve trunks is sometimes needed.