**Question:** A 56-year-old male is burned while sleeping in his home. His right upper and lower extremity and the anterior aspect of the upper chest have extensive second-degree burns. The extent of the burn is calculated to represent what percentage of body surface area?

**Core Concept:** The "rule of nines" is a widely used method for estimating the extent of burns in adults, based on the distribution of body surface areas. It is derived from the human body's division into nine sections, each with a percentage representation:

1. Each arm equals 9%
2. The head equals 9%
3. The anterior and posterior trunk each equals 18%
4. Each leg equals 18%

**Core Concept Explanation:** In this scenario, the patient has extensive second-degree burns on his right upper and lower extremity and anterior aspect of the upper chest. These burns cover the right arm (9% burn), anterior trunk (18% burn), and right leg (18% burn).

**Why the Correct Answer is Right:** The patient has burns in three sections according to the rule of nines:

A. Right arm (9% burn): This burn corresponds to the right arm's 9% representation in the rule of nines.
B. Anterior trunk (18% burn): The right anterior trunk covers both the chest and abdomen, which correspond to the 18% representation in the rule of nines.
C. Right leg (18% burn): This burn corresponds to the right leg's 18% representation in the rule of nines.

**Why Each Wrong Option is Incorrect:**

D. The patient does not have a burn covering the entire head, which corresponds to 9% in the rule of nines.
E. The patient does not have a burn covering the entire upper limb and lower limb, which correspond to 18% in the rule of nines.

**Clinical Pearl:** The "rule of nines" is a useful mnemonic to estimate the extent of burns in adults, helping clinicians determine the required level of care and treatment. This method is based on the human body's division into nine sections (arms, legs, torso, head, and neck).

**Correct Answer:** The correct answer is A (9%), as the patient has extensive burns in the right arm, which corresponds to 9% burn according to the rule of nines.

**Why Each Wrong Option is Incorrect:**

D. The patient does not have a burn covering the entire head, which corresponds to 9% in the rule of nines, so option D is incorrect.
E. The patient does not have a burn covering the entire upper limb and lower limb, which correspond to 18% in the rule of nines, so option E is incorrect.

**Clinical Pearl:** The rule of nines is a simple and quick method to estimate the body surface area of burns in adults, aiding doctors in assessing the severity and treatment requirements. Understanding this method aids in making appropriate decisions regarding the patient's management