**Core Concept**
The question refers to the rule of nines, a method used to estimate the total body surface area (TBSA) affected by a burn. This concept is crucial in burn management to assess the extent of injury and guide treatment decisions.

**Why the Correct Answer is Right**
The rule of nines divides the body into areas that correspond to 9% of the total body surface area. The lower limbs are each considered to be 18% of the TBSA. This is because the lower limbs are relatively larger compared to the upper limbs. The rule of nines is a simplified estimate and may not accurately reflect the actual TBSA in all cases, but it provides a useful guideline for initial assessment and management.

**Why Each Wrong Option is Incorrect**
**Option A:** 4.50% is the estimated TBSA for the head and neck, not the lower limbs.
**Option B:** 9% is the estimated TBSA for one arm or one leg, but not the lower limbs specifically.
**Option C:** 13.50% is an incorrect estimate for the TBSA of one lower limb.

**Clinical Pearl / High-Yield Fact**
When assessing a burn injury, it's essential to remember that the rule of nines is only an estimate and may not accurately reflect the extent of injury, especially in patients with circumferential burns, burns on the trunk, or burns in children. Always consider other methods, such as the Lund-Browder chart, to obtain a more accurate estimate of TBSA.

**✓ Correct Answer: D. 18%**