459.The answer is d.(Moore and Dalley, p 822.)In the arm, the musculo-
cutaneous nerve passes through the coracobrachialis muscle (answer b).
The radial nerve, which lies in the musculospiral groove, passes between the
long and medial heads of the triceps brachii muscle (answer a)in company
with the profunda brachii artery. It is here that the nerve and artery are in
jeopardy in the event of a mid-humeral fracture. In the forearm, the median
nerve courses between the humeral and ulnar heads of the pronator teres.
As the ulnar nerve courses behind the medial epicondyle, it passes between
the humeral and ulnar heads of the flexor carpi ulnaris (answer c)as it
enters the forearm. In each instance, the nerve innervates the muscle that it
pierces.
460.The answer is a.(Moore and Dalley, pp 733–734, 795.)The area
marked Z points to the approximate location of the spiral (radial) groove.
This shallow depression, on the posterior (dorsal) aspect of the humeral
shaft, accommodates the radial nerve and the deep (profunda) brachial
vessels. A midline fracture of the humerus may rupture the blood vessels,
causing a hematoma that would compress and impair the ability of the
radial nerve to conduct information to the extensor muscles of the wrist and
digits. A more severe fracture may transect the radial nerve, causing paralysis
of the same muscles, resulting in wrist-drop. These muscles include the fol-
lowing: brachioradialis, extensor carpi radialis longus, extensor carpi radialis
brevis, extensor digitorum communis, extensor digiti minimi, extensor carpi
ulnaris, supinator, abductor pollicis longus, extensor pollicis longus, exten-
sor pollicis brevis, and the extensor indicis. The causes of other palsies listed
in this question are injuries due to the nerves within parentheses: total claw
hand palsy [median and ulnar nerves; (answer b)]; clawing of digits 4 and 5
[ulnar nerve; (answer d)]; waiter’s tip palsy [C5, C6 roots of the brachial
plexus; upper trunk of the brachial plexus; (answer c)]; and Erb-Duchenne
palsy. Dupuytren’s contracture (answer e)is caused by a thickening of the
palmar aponeurosis and occurs more frequently in diabetrcs.
461.The answer is d.(Moore and Dalley, pp 760–761.). The surgical neck of
the humerus is the narrow area located just distal to the head and anatomi-
cal neck of the humerus (the area marked X in the radiograph for question
460).The posterior (dorsal aspect) of the surgical neck is transversed by
the axillary nerve (C5, C6; posterior/dorsal cord of the brachial plexus)
and the accompanying posterior circumflex humeral vessels. A fracture
Extremities and Spine Answers 591