The muscles that move the thumb are activated by the median nerve. Keep the hand flat, palm level and facing the ceiling and the wrist slightly extended backwards during this test, as shown in the figure below.

First, ask the patient to bring his thumb up in front of the index finger but as far away from it as possible, in the way shown to the left of the figure below. Focus your attention on the degree of movement that is possible at the base of the thumb rather than the tip. Can the patient achieve this starting position for the test? Is movement full?

Now test the strength of this movement as shown to the right of the figure below– seeing if the individual can resist the pressure you apply to the side of the thumb. Ask the patient to stare at you during the test, while you try to push his thumb out and across, away from his little finger.