Anterior interosseous nerve motor

Name of test

Pinch Grip Test

What it tests

The Pinch Grip Test assesses flexion of both the interphalangeal joint of the thumb and the distal interphalangeal joint of the index finger. Since these actions are normally controlled by the flexor pollicus longus and flexor digitorum profundus (lateral most tendon) muscles respectively, this test reliably measures function of the anterior interosseous nerve.

How to do it

The patient is asked to bring the tips of the index finger and thumb together so as to form the letter O, as is done in an "O.K sign".

The normal response

In a normal response, the patient will be able to bring both finger tips together to form the letter O.

What it means if not normal

A patient with a lesion to the anterior interosseous nerve will not be able to form the letter O, as a result of weakness in the ability to flex the thumb and index finger at their distal most joints. Instead, the patient will form more of a triangular looking structure, due to maintained extension at these joints.

Comments

A second maneuver that can be used to assess the function of the anterior interosseous nerve is to test the action of the pronator quadratus muscle. To isolate the effects of this muscle, the patient should be instructed to fully flex and supinate the forearm at the elbow. In addition, the patient’s elbow should be at his/her side (shoulder fully adducted). Clasp the patient’s hand, and instruct him/her to pronate it against resistance. Compare both right and left sides, in order to get a sense for whether there may be unilateral weakness suggestive of a lesion to the anterior interosseous nerve on the affected side.

Citations

2853888

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