A lesion of the anterior interosseous nerve can result in a number of clinical findings.


The patient may experience aching or discomfort in the volar aspect of the forearm.


There may be atrophy in forearm muscles, resulting in a decreased circumference compared to the opposite side.


There is motor weakness (due to involvement of the deep flexor muscles) in the:

(1) thumb

(2) index finger

(3) middle finger (variable)


Circle sign: The patient is unable to make an "O" with the thumb and index finger.


There is no numbness since the nerve does not supply the skin.


Differential diagnosis:

(1) rheumatoid arthritis

(2) radial or ulnar fracture

(3) pseudo anterior interosseous nerve syndrome (lesion of median nerve more proximally with involvement of fibers to the anterior interosseous nerve)

(4) mononeuritis (Parsonage-Turner syndrome, other)

(5) lesion of the flexor pollicis longus tendon


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