A 17-year-old male presented with complaints of severe shoulder pain along with his left arm hanging by the side with some external rotation. The patient suffered a blow to his left arm while playing football. The doctor on duty ordered a radiograph of the injured site What is the most likely nerve injured?

**Core Concept**
The question is testing the student's knowledge of the anatomy and innervation of the shoulder joint, as well as the clinical presentation of a specific type of nerve injury.

**Why the Correct Answer is Right**
The patient's presentation of severe shoulder pain, arm hanging by the side with external rotation, and a history of a blow to the arm is classic for a nerve injury affecting the musculocutaneous nerve, axillary nerve, and radial nerve. However, the most likely nerve injured is the axillary nerve, which is responsible for the innervation of the deltoid muscle and the teres minor muscle. The axillary nerve is also the nerve most commonly injured in shoulder dislocations, which is consistent with the patient's history of a blow to the arm. The axillary nerve runs through the quadrangular space, which is a common site of injury in shoulder dislocations.

**Why Each Wrong Option is Incorrect**
**Option A:** The musculocutaneous nerve is responsible for the innervation of the biceps brachii and brachialis muscles, but it is not typically injured in shoulder dislocations.

**Option B:** The radial nerve is responsible for the innervation of the triceps brachii and is often injured in fractures of the humerus, but it is not typically injured in shoulder dislocations.

**Option C:** The suprascapular nerve is responsible for the innervation of the supraspinatus and infraspinatus muscles, but it is not typically injured in shoulder dislocations.

**Clinical Pearl / High-Yield Fact**
The axillary nerve is often injured in shoulder dislocations, and this can result in weakness of the deltoid muscle and the teres minor muscle, leading to a characteristic "drooping" of the arm.

**Correct Answer: C. The axillary nerve.**