A young patient’s median nerve is injured by a supracondylor fracture of the humerus. The resulting motor deficits may include all of the following EXCEPT which one?
- Weakness of pronation
- Weakness of ulnar deviation of the wrist
- Loss of thumb opposition
- Loss of abduction of the index and middle fingers
- Loss of index and middle finger flexion
The median nerve passes anterior to the distal humerus just proximal to the elbow joint, where it may be damaged by a displaced proximal fragment from supracondylar fracture.
Motor deficits arising from median nerve injury at this level include:
- Loss of pronation (turning the hand upwards) (paralysis of pronator teres & pronator quadratus)
- Weakness of wrist flexion and radial deviation (paralysis of flexor carpi radialis),
- Loss of index and middle finger flexion (paralysis of all flexor digitorum superficialis and of the radial half of flexor digitorum profundus as well as the 1st and 2nd lumbricals) – the hand of benediction sign when trying to make a fist.
- Inability to flex or oppose the thumb (paralysis of the LOAF muscles – lumbricals 1 & 2, opponens pollicis, abductor pollicis brevis and flexor pollicis brevis)
(Finger abduction and adduction is a function of the palmar interosseous muscles, all of which are innervated by the ulnar nerve)