Which muscle will be weak with anterior interosseous nerve entrapment but not weak with carpal tunnel syndrome?

Which muscle will be weak with anterior interosseous nerve entrapment but not weak with carpal tunnel syndrome?

• A. FPL
• B. FDP (lateral half)
• C. Pronator Quadratus
• D. FDS

Answer: (C)

Anterior interosseous nerve entrapment selectively weakens the deep forearm flexors that this nerve supplies, while carpal tunnel syndrome, which compresses the median nerve at the wrist, does not affect those proximal branches. The muscle in question is innervated solely by the anterior interosseous nerve, so its weakness points to an AIN issue rather than CTS. Pronator quadratus receives its motor input exclusively from the anterior interosseous nerve, making it the best discriminator: it will be weak with AIN entrapment but spared with carpal tunnel syndrome.

Anterior interosseous nerve entrapment selectively weakens the deep forearm flexors that this nerve supplies, while carpal tunnel syndrome, which compresses the median nerve at the wrist, does not affect those proximal branches. The muscle in question is innervated solely by the anterior interosseous nerve, so its weakness points to an AIN issue rather than CTS. Pronator quadratus receives its motor input exclusively from the anterior interosseous nerve, making it the best discriminator: it will be weak with AIN entrapment but spared with carpal tunnel syndrome.