A 21-year-old patient has a lesion of the upper trunk of the brachial plexus (Erb– Duchenne paralysis). Which of the following is the most likely diagnosis?
(A) Paralysis of the rhomboid major
(B) Inability to elevate the arm above the
horizontal
© Arm tending to lie in medial rotation
(D) Loss of sensation on the medial side of
the arm
(E) Inability to adduct the thumb
The answer is C. A lesion of the upper trunk of the brachial plexus results in a condition
called “waiter’s tip hand,” in which the arm tends to lie in medial rotation because of
paralysis of lateral rotators and abductors of the arm. The long thoracic nerve, which
arises from the root (C5–C7) of the brachial plexus, innervates the serratus anterior muscle
that can elevate the arm above the horizontal. The dorsal scapular nerve, which arises
from the root (C5), innervates the rhomboid major. The medial side of the arm receives
cutaneous innervation from the medial brachial cutaneous nerve of the medial cord. The
adductor pollicis is innervated by the ulnar nerve.