A 28-year-old woman is admitted to the burn unit following a house fire. On examination, she has full-thickness burns over the entire posterior trunk (back and buttocks), both posterior lower limbs, and the posterior aspect of both upper limbs. Using the Rule of Nines, what is the total percentage of BSA affected by this burn injury?

Explanation

## Rule of Nines Application: Posterior Surface Burns **Key Point:** The Rule of Nines is a rapid, standardized method for estimating burn surface area in adults. Each major body region is assigned a percentage that is a multiple of 9. ### Standard Rule of Nines (Adult) | Body Region | Total % | Anterior | Posterior | |---|---|---|---| | Head & Neck | 9% | 4.5% | 4.5% | | Each Upper Limb | 9% | 4.5% | 4.5% | | Anterior Trunk | 18% | 18% | — | | Posterior Trunk (back + buttocks) | 18% | — | 18% | | Each Lower Limb | 18% | 9% | 9% | | Perineum | 1% | — | — | ### Breakdown of Affected Areas in This Patient | Body Region | Calculation | Total | |---|---|---| | Posterior trunk (back + buttocks) | 18% (single region) | **18%** | | Posterior aspect of both upper limbs | 4.5% × 2 | **9%** | | Posterior aspect of both lower limbs | 9% × 2 | **18%** | | **Grand Total** | | **45%** | **Calculation:** - Posterior trunk: **18%** - Both posterior upper limbs: 4.5% + 4.5% = **9%** - Both posterior lower limbs: 9% + 9% = **18%** - **Total = 18 + 9 + 18 = 45%** The stem explicitly states burns over the posterior trunk, both posterior lower limbs, and the posterior aspect of both upper limbs — no mention of the head or neck. Applying the Rule of Nines strictly to the described regions yields **45%**. **High-Yield:** Burns >20% BSA (partial thickness) or >10% BSA (full thickness) are classified as **major burns** requiring burn center referral. This patient with 45% full-thickness BSA burns requires: 1. Immediate airway assessment (inhalation injury risk) 2. Fluid resuscitation using the **Parkland formula**: `4 mL × kg body weight × % BSA burned` of Ringer's Lactate over 24 hours (half in first 8 hours, half in next 16 hours) 3. Monitoring for compartment syndrome and systemic complications **Clinical Pearl:** The Rule of Nines is used for adults; the **Lund and Browder chart** is preferred for children, as it accounts for age-related differences in body proportions (larger head, smaller legs in infants). *(Reference: Textbook of Forensic Medicine & Toxicology – Reddy; also Park's Textbook of Preventive and Social Medicine)*