According to the Rule of Nines for adult burn surface area estimation, what percentage of total body surface area (TBSA) is covered by each lower limb?

Explanation

## Rule of Nines — Adult Body Surface Area Distribution **Key Point:** The Rule of Nines is the most widely used rapid assessment tool for estimating TBSA involvement in burn injuries. It divides the body into segments, each representing 9% or a multiple thereof. ### Adult Rule of Nines Breakdown | Body Region | TBSA % | | --- | --- | | Head and neck | 9% | | Each upper limb (arm + forearm + hand) | 9% | | Anterior trunk | 18% | | Posterior trunk | 18% | | Each lower limb (thigh + leg + foot) | 18% | | Perineum/genitalia | 1% | | **Total** | **100%** | **High-Yield:** Each lower limb = **18%** (not 9%). This is a common source of confusion. The lower limbs are larger than the upper limbs and the head, so they account for 18% each. **Clinical Pearl:** Rapid TBSA estimation is critical in the first 24–48 hours post-burn for fluid resuscitation decisions. Underestimation leads to inadequate resuscitation and shock; overestimation leads to fluid overload and pulmonary edema. ### Pediatric Modification (Rule of Nines for Children) In children <10 years, the head accounts for 18% (not 9%) and each lower limb accounts for 13.5% (not 18%), reflecting the proportionally larger head and smaller limbs in pediatric anatomy. **Mnemonic:** **"9-18-1 Rule"** - **9%** = Head, each arm - **18%** = Each leg, anterior trunk, posterior trunk - **1%** = Perineum