**Core Concept**
The brachial plexus is a complex network of nerves that arise from the spinal cord, providing motor and sensory innervation to the upper limb. A brachial plexus block is a regional anesthesia technique used to anesthetize the upper limb, typically for surgical procedures.

**Why the Correct Answer is Right**
The most commonly used approach to brachial plexus block is the supraclavicular approach. This approach involves inserting a needle above the clavicle, targeting the brachial plexus as it passes through the interscalene groove. The supraclavicular approach allows for a high success rate and rapid onset of anesthesia, making it a preferred choice for many surgeons.

• The supraclavicular approach targets the brachial plexus at its most compact and accessible point.
• This approach allows for a high concentration of local anesthetic to be delivered to the nerves, resulting in effective anesthesia.
• The supraclavicular approach is also associated with a lower risk of complications, such as pneumothorax, compared to other approaches.

**Why Each Wrong Option is Incorrect**
**Option A:** The interscalene approach, while commonly used, is not the most commonly used approach to brachial plexus block.
**Option A is incorrect because it targets the brachial plexus at a more proximal point, resulting in a higher risk of complications and a slower onset of anesthesia.**

**Option B:** The axillary approach is not a common approach to brachial plexus block.
**Option B is incorrect because it targets the nerves at a more distal point, resulting in a lower success rate and a higher risk of incomplete anesthesia.**

**Option C:** The infraclavicular approach is not the most commonly used approach to brachial plexus block.
**Option C is incorrect because it targets the brachial plexus at a more variable point, resulting in a lower success rate and a higher risk of complications.**

**Clinical Pearl / High-Yield Fact**
The supraclavicular approach is often associated with a higher risk of pneumothorax, so it's essential to use ultrasound guidance to avoid this complication.

**Correct Answer: C. Supraclavicular approach**