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

Question

Accepted Answer

B. Dorsal surfaces of the trunk and limbs. ## 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.*

Answer

A. Face and neck region

Answer

C. Ventral surfaces of the trunk and limbs

Answer

D. Dependent areas over bony prominences

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

Mechanism of Lividity Formation

Position-Specific Lividity Patterns

Why Option B (Ventral surfaces) is WRONG

Clinical Pearl — Discordance Between Lividity and Position

Blanching vs. Fixation

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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