A 32-year-old man is admitted to the emergency department after a severe car crash. Radiographic examination reveals multiple fractures of his right upper limb. A surgical procedure is performed and metallic plates are attached to various bony fragments to restore the anatomy. Five months postoperatively the patient visits the outpatient clinic. Upon physical examination the patient can abduct his arm and extend the forearm, but the sensation of the forearm and hand is intact; however, the hand grasp is very weak, and he cannot extend his wrist against gravity. Which of the following nerves was most likely injured during the surgical procedure?

**Core Concept**
The question requires an understanding of the anatomy and function of the nerves innervating the upper limb, particularly those responsible for motor control of the forearm and hand. The radial nerve is a key nerve involved in the innervation of the extensor muscles of the forearm and wrist.

**Why the Correct Answer is Right**
The radial nerve is responsible for the innervation of the extensor muscles of the forearm, including the extensor carpi radialis brevis, extensor carpi radialis longus, and extensor digitorum. These muscles are involved in the extension of the wrist and fingers. The radial nerve also innervates the supinator muscle, which is responsible for the supination of the forearm. The clinical findings in this patient, including weakness in hand grasp and inability to extend the wrist against gravity, suggest an injury to the radial nerve. The patient's ability to abduct his arm and extend the forearm suggests that the axillary nerve, which innervates the deltoid muscle, was not injured.

**Why Each Wrong Option is Incorrect**
**Option A (Median Nerve):** The median nerve is primarily responsible for the innervation of the flexor muscles of the forearm and the thenar muscles of the thumb. Injury to the median nerve would result in weakness of thumb opposition and flexion of the fingers, which is not consistent with the patient's clinical presentation.

**Option B (Ulnar Nerve):** The ulnar nerve is responsible for the innervation of the intrinsic muscles of the hand, including the interosseous and lumbrical muscles. Injury to the ulnar nerve would result in weakness of hand grasp and finger spread, but the patient's ability to extend the fingers suggests that the ulnar nerve was not injured.

**Option C (Axillary Nerve):** The axillary nerve is responsible for the innervation of the deltoid muscle, which is involved in the abduction of the arm. The patient's ability to abduct his arm suggests that the axillary nerve was not injured.

**Clinical Pearl / High-Yield Fact**
It is essential to remember that the radial nerve is at risk during surgical procedures involving the upper limb, particularly those involving the humerus. The radial nerve can be injured due to compression or traction on the nerve as it wraps around the shaft of the humerus.

**Correct Answer: C. Radial Nerve**

✓ Correct Answer: B. Radial nerve at the distal third of the humerus