Anterior interosseous syndrome affects which muscles leading to the OK sign?

Study for the NBCOT Hand Injuries and Intervention Test. Prepare with flashcards and multiple choice questions, each question offers hints and explanations. Get ready for success!

Multiple Choice

Anterior interosseous syndrome affects which muscles leading to the OK sign?

Anterior interosseous syndrome knocks out the deep motor branch of the median nerve that powers the deep forearm flexors. The ability to perform the tip-to-tip pinch (the OK sign) depends on flexing the thumb’s IP joint with the flexor pollicis longus and flexing the index finger’s DIP joint with the flexor digitorum profundus to the index finger. When these two muscles are weakened, you can’t bring the tips together, so the OK sign is impaired. The extensor pollicis longus, which extends the thumb, is controlled by a different nerve (the posterior interosseous) and would not be affected by AIN palsy. Similarly, flexor carpi ulnaris is an ulnar-nerve–innervated wrist flexor, and pronator teres is a proximal median nerve target; neither loss explains the specific pinch deficit seen with AIN injury.

Anterior interosseous syndrome knocks out the deep motor branch of the median nerve that powers the deep forearm flexors. The ability to perform the tip-to-tip pinch (the OK sign) depends on flexing the thumb’s IP joint with the flexor pollicis longus and flexing the index finger’s DIP joint with the flexor digitorum profundus to the index finger. When these two muscles are weakened, you can’t bring the tips together, so the OK sign is impaired. The extensor pollicis longus, which extends the thumb, is controlled by a different nerve (the posterior interosseous) and would not be affected by AIN palsy. Similarly, flexor carpi ulnaris is an ulnar-nerve–innervated wrist flexor, and pronator teres is a proximal median nerve target; neither loss explains the specific pinch deficit seen with AIN injury.

More practice questions