Which is the most common site of post-mortem lividity in a body found in the supine position?

Explanation

## Post-mortem Lividity (Livor Mortis) — Distribution **Key Point:** Post-mortem lividity appears in **dependent areas** due to gravitational pooling of blood in capillaries and venules after circulation ceases. In a **supine position**, the **dorsal (posterior) surfaces** are the most dependent, so lividity appears there. ### Mechanism of Lividity Formation 1. Immediately after death, blood pressure drops to zero 2. Red blood cells settle in dependent vessels due to gravity 3. Deoxyhaemoglobin imparts a purple-red discoloration 4. Typically appears 30 minutes to 2 hours after death 5. Becomes fixed (non-blanching) after 8–12 hours due to RBC lysis and haemoglobin diffusion into surrounding tissues ### Position-Specific Lividity Patterns | Body Position | Most Common Lividity Site | Reason | |---|---|---| | **Supine (lying on back)** | **Dorsal surfaces of trunk and limbs** | Posterior surfaces are dependent; gravity pools blood there | | **Prone (face down)** | Ventral surfaces of trunk and limbs | Anterior surfaces are dependent | | **Lateral decubitus** | Lateral aspect of the side on which body lies | Unilateral dependent pooling | | **Hanging** | Head, neck, face, hands, feet | Venous congestion in lowermost parts | **High-Yield:** In a supine body, livor mortis characteristically appears on the **dorsal (posterior) surfaces** — posterior trunk, posterior limbs, and the back of the neck. Areas in contact with a firm surface (e.g., scapulae, sacrum, heels) may be spared due to pressure occluding capillaries, creating the classic "contact pallor" pattern. This is the standard teaching in *Modi's Medical Jurisprudence and Toxicology* and *Parikh's Textbook of Medical Jurisprudence*. ### Why Option B (Ventral surfaces) is WRONG In the supine position, the ventral (anterior) surfaces face **upward** — they are the non-dependent surfaces. Blood does not pool upward against gravity. Lividity on ventral surfaces in a supine body would indicate the body was **moved** after death, which is a forensic red flag. ### Clinical Pearl — Discordance Between Lividity and Position If a body is found supine but shows **ventral** lividity, it strongly suggests post-mortem repositioning — a critical finding in homicide investigations. Fixed lividity that does not shift with repositioning after 8–12 hours confirms the original position of death. ### Blanching vs. Fixation - **Early livor (< 8–12 hours):** Blanches with pressure (reversible) - **Fixed livor (> 12 hours):** Does not blanch; RBCs have lysed and haemoglobin has diffused into tissue **Mnemonic:** **DEPENDENT = DORSAL in SUPINE** — In a supine body, the back (dorsal surface) is the lowest (dependent) region where gravity pulls blood. *Reference: Parikh's Textbook of Medical Jurisprudence, Forensic Medicine and Toxicology, 7th ed.; Modi's Medical Jurisprudence and Toxicology.*