National Physical Therapy Examination (NPTE) Practice Exam

Which nerve is affected if a patient cannot oppose the tip of their thumb to the tip of their index finger?

1. Posterior interosseous nerve

2. Anterior interosseous nerve

3. Ulnar nerve

4. Median nerve

The correct answer is: Anterior interosseous nerve

The inability to oppose the tip of the thumb to the tip of the index finger directly indicates an issue with the muscles responsible for thumb opposition, particularly the opponens pollicis muscle. This muscle is innervated by the median nerve. The anterior interosseous nerve, which branches from the median nerve, primarily innervates certain deep muscles of the forearm, such as the flexor pollicis longus and the lateral half of the flexor digitorum profundus. It does not innervate the muscles necessary for thumb opposition, which means that damage to this nerve would not result in difficulty with thumb opposition specifically. In contrast, the ulnar nerve and posterior interosseous nerve are responsible for different muscle groups not directly involved in this precise function. The ulnar nerve primarily innervates the intrinsic muscles of the hand (except for those innervated by the median nerve), and the posterior interosseous nerve primarily serves the extensor muscles of the forearm. In this context, the correct answer relates to the function of thumb opposition, underscoring the role of the median nerve, which facilitates this crucial movement through its innervation of the opponens pollicis.