Question.

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?

  1. Weakness of pronation
  2. Weakness of ulnar deviation of the wrist
  3. Loss of thumb opposition
  4. Loss of abduction of the index and middle fingers
  5. Loss of index and middle finger flexion


Answer.

D

Explanation.

 

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:

  1. Loss of pronation (turning the hand upwards) (paralysis of pronator teres & pronator quadratus)
  2. Weakness of wrist flexion and radial deviation (paralysis of flexor carpi radialis),
  3. 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.
  4. 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)