Following an incised wound in the front of the wrist, the subject is unable to oppose the tips of the little finger and the thumb. The nerve (s) involved is/are –
**Core Concept**
The question is testing the student's knowledge of the motor innervation of the hand, specifically the function of the thenar muscles and the lumbrical muscles. The thenar muscles are responsible for thumb opposition, while the lumbrical muscles help in finger flexion and opposition.
**Why the Correct Answer is Right**
The motor innervation of the hand is primarily provided by the median nerve (C8-T1) and the ulnar nerve (C8-T1). The median nerve innervates the thenar muscles, including the opponens pollicis, abductor pollicis brevis, and flexor pollicis brevis. These muscles work together to oppose the thumb. The ulnar nerve innervates the lumbrical muscles to the little finger and ring finger, which help in finger flexion and opposition. The inability to oppose the tips of the little finger and the thumb suggests a lesion affecting the motor innervation to these muscles. Given the location of the wound, the median nerve is more likely to be involved.
**Why Each Wrong Option is Incorrect**
**Option A:** The radial nerve is responsible for the innervation of the extensor muscles of the wrist and fingers, which are not involved in thumb opposition. Therefore, a lesion affecting the radial nerve would not result in the inability to oppose the tips of the little finger and the thumb.
**Option B:** The musculocutaneous nerve innervates the biceps brachii and brachialis muscles, which are not involved in hand movements. Therefore, a lesion affecting the musculocutaneous nerve would not result in the inability to oppose the tips of the little finger and the thumb.
**Option C:** The axillary nerve is responsible for the innervation of the deltoid and teres minor muscles, which are involved in shoulder movements. Therefore, a lesion affecting the axillary nerve would not result in the inability to oppose the tips of the little finger and the thumb.
**Clinical Pearl / High-Yield Fact**
The median nerve is often injured in wrist injuries due to its superficial location and proximity to the wrist joint. A thorough examination of the hand should always include testing for median nerve function, including thumb opposition and little finger flexion.
**Correct Answer:** C. Ulnar nerve injury is not the correct answer, it is the median nerve injury that is more likely to be involved.