T-1 Motor–First Dorsal Interossei

Name of test

Finger ABduction

What it tests

First dorsal interossei

How to do it

With the patients fingers spread, grasp the patient’s finger’s between the examiner’s thumb and index finger. Push the fingers back together while the patient resists with interossei activity.

The normal response

Grade 5 strength. The examiner is able to overcome the patient’s interossei strength with moderate difficulty

What it means if not normal

Comments

The dorsal interossei muscles are innervated by the deep ulnar nerve (C8, T1).

The dorsal interossei muscles are responsible for finger ABduction, while the palmar interossei muslces are responsible for finger ADduction.

To remember the difference, rest your hand comfortably on the surface of a table. Attempt to spread your fingers maximally and notice how your fingers lift off the table (dorsally) as your palm remains in contact. Thus your dorsal interossei, which ABduct your fingers also cause them to move dorsally.

Citations

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