This patient presents with anterior interosseous nerve (AIN) syndrome and is often seen in conjunction with brachial neuritis (Parsonage-Turner Syndrome).
AIN sydrome leads to motor palsies of the flexor pollicis longus and the two radial profundus tendons leading to the clincal image shown in Figure A. The pronator quadratus is also involved and can be tested with the elbow held in a flexed position to neutralize the humeral head of the pronator teres muscle. No sensory changes occur and Electromyographic (EMG) and nerveconduction (NCV)studies are often helpful in establishing the diagnosis. Anterior interosseous nerve syndrome usually resolves with time, particularly if the lesion is secondary to neuritis. Observation for 3 to 6 months with splinting at 90 degrees is favored before surgical treatment.
Green DP, Hotchkiss RN, Pederson WC (eds): Entrapment and compression neuropathy, in Green’s Operative Hand Surgery, ed 4. Phila, PA, 1999. pp 1404-1447