Nerve injury

Nerve injuries may occur as a result of blunt, penetrating or crush injuries.

Median nerve

The median nerve motor and sensory function should be tested as follows:

1. Thumb abduction with the palm up, raising the thumb to perpendicular (AbPB)
2. Sensation over the palmar index finger, thumb, and proximal palm near the thenar eminence
3. Weakness or absence of flexion of the IPJ of the thumb (FPL) and the DIPJ of the index finger (FDP) against resistance, if present, are due to a proximal lesion (anterior interosseous nerve).

Ulnar nerve

The ulnar nerve motor and sensory function should be tested as follows:

1. Spread the fingers against resistance (dorsal interossei)
2. Adduct the fingers against resistance (palmar interossei)
3. Thumb adduction (AdP) against the index finger, and with paper interposed and pulled away (Froments sign look for use of FPL, supplied by the median nerve, to assist adduction)
4. Sensation over ulnar side of the hand and little finger. It also supplies the dorsal ulnar region of the hand via the dorsal cutaneous branch of the ulnar nerve

Radial nerve

The radial nerve motor and sensory function should be tested as follows:

1. Finger and wrist extension
2. Sensation to the dorsal first web space of the hand

Sensation

Sensation is best tested with two-point discrimination [7]. Two-point discrimination greater than 6 mm static or 4 mm moving is abnormal [2-3]. Injured and non-injured fingers should be compared. A paper clip provides an accessible testing tool [8].

As patients may guess correctly by chance, the test should be repeated at least 2-4 times on each side of the digit. Less than 80% accuracy or indeterminate testing suggests the possibility of digital nerve injury [9].

A sensory nerve deficit also implies a possible digital arterial injury given the close proximity of the two structures.

Dry, shiny skin

Nerve injury is also suggested by dry, shiny skin that does not wrinkle when immersed in water [10] this is due to a loss of sympathetic innervation.

The tactile adherence test [11] can also prove useful, looking for a loss of friction in the denervated area due to absent sweating.

It should be noted that all the above tests are subjective.

Early recognition

The early recognition of nerve injury is important as primary repair has been found to be superior to delayed repair [12].

Results of digital nerve repair are variable; in a review of 109 cases, no patients regained normal sensation, although 83% did achieve sensory results that could be classed as good [13].

Results are better in children than in adults [14].