You are seeing a six year old with a type III supracondylar fracture of the humerus. He fell on his outstretched arm while playing on some monkey bars. He has some mild difficulty flexing his thumb when he makes a fist. Where is his neurapraxia?
Answer: The Anterior Interosseous Nerve
It is the most common nerve injured in extension type supracondylar humerus fractures. It arises from the median nerve 5cm above medial epicondyle. It innervates the flexor pollicis longus (thumb IP joint flexion) and the flexor digitalis profundus (flexion of index and middle finger DIP joint).
Ulnar neurapraxia occurs in flexion type supracondylar fractures. The ulnar nerve conveys sensory innervation to the dorsal ulnar and volar ulnar 1 1/2 fingers (#4 and 5) and motor to the hypothenar and intrinsic hand muscles.
With a Radial N. injury (which is rare in elbow fractures) patients cannot extend the thumb and wrist and experience sensory loss to the dorsum of thumb, the first web space, and the hand to middle third of ring finger and distal to PIP.
Median N. injuries result in loss of sensation to the volar thumb and radial 2 1/2 fingers. Also patients cannot oppose or flex the thumb, have weak flexion/radial deviation of the wrist and impaired pronation as well.
