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

Explanation

## Rule of Nines in Adult Burns **Key Point:** The Rule of Nines is a rapid method for estimating TBSA involvement in burn injuries, essential for fluid resuscitation and triage decisions. ### Adult Distribution (Rule of Nines) | Body Region | Percentage TBSA | | --- | --- | | Head and neck | 9% | | Each upper limb | 9% | | Chest | 9% | | Abdomen | 9% | | Each lower limb | 18% | | Back and buttocks | 18% | | Perineum/genitalia | 1% | | **Total** | **100%** | **High-Yield:** Each lower limb (from inguinal ligament to toes) = **18% TBSA**. This is double the percentage of each upper limb because the lower limbs are larger and carry more body mass. ### Clinical Pearl The Rule of Nines allows rapid bedside estimation without need for detailed measurement. In pediatric patients (< 10 years), the head accounts for 18% and each lower limb for 13.5%, reflecting the proportionally larger head-to-body ratio in children. **Mnemonic:** **"9-18-9 Rule"** — Head/neck 9%, upper limbs 9% each, trunk 18% (chest + abdomen), lower limbs 18% each, back 18%. ### Why This Matters Accurate TBSA estimation determines: - Fluid resuscitation volume (Parkland formula: 4 mL × kg × %TBSA) - Admission to burn centre criteria (≥ 10% TBSA in adults warrants specialist care) - Prognosis and mortality prediction