A boy presents with an injury to the medial epicondyle of the humerus. Which of the following would not be seen -
Medial epicondyle fracture causes injury to the ulnar nerve.
In ulnar nerve palsy only following muscles of 3rd & 4th fingers are paralysed:-

i) Palmar & Dorsal interossei
ii) 3rd & 4th lumbricals
iii) Hypothenar muscles

However, extensors of these two fingers are not paralysed which are supplied by the radial nerve.

About other options

The weakness of ulnar deviation & flexion is due to paralysis of FCU and medial half of FDP.
There atrophy of hypothenar eminence and sensory loss over the hypothenar area.