Regarding rigor mortis, all of the following statements are correct EXCEPT:

Explanation

## Rigor Mortis: Onset, Progression, and Resolution ### Definition and Mechanism **Key Point:** Rigor mortis is a post-mortem stiffening of muscles caused by depletion of adenosine triphosphate (ATP) and accumulation of lactic acid, leading to permanent cross-linking of actin and myosin filaments. ### Onset and Progression **High-Yield:** Rigor mortis typically begins in the eyelids, muscles of mastication, and neck, then progresses in a cephalocaudal (downward) direction to the trunk and limbs. This pattern is consistent and predictable. ### Timeline and Factors Affecting Onset | Factor | Effect on Rigor Mortis | | --- | --- | | Normal conditions | Appears 2–3 hours post-mortem | | Heat/high temperature | Accelerates onset (heat accelerates enzyme activity) | | Cold/low temperature | Delays onset | | Prolonged illness/starvation | Delayed onset (reduced muscle glycogen) | | Cachexia | Delayed or absent rigor | | Muscular exertion before death | May appear earlier | ### Resolution Timeline **Warning:** The statement that rigor mortis is "completely resolved by 48–72 hours in all environmental conditions" is **INCORRECT**. Resolution depends heavily on environmental factors: - In cool environments: rigor may persist for 8–10 days or longer - In warm/hot environments: rigor resolves faster (3–5 days) due to bacterial decomposition and muscle autolysis - In cold storage (refrigeration): rigor may persist indefinitely until thawing occurs **Clinical Pearl:** The absence of rigor mortis does not mean death occurred recently — it may indicate advanced decomposition, extreme environmental conditions, or conditions that prevent rigor formation (cachexia, prolonged illness). ### Why Each Statement Is Evaluated 1. **Cephalocaudal progression** — TRUE; this is the classic pattern taught in all forensic medicine texts 2. **Delayed onset in illness/starvation** — TRUE; reduced muscle glycogen delays rigor formation 3. **ATP depletion and actin-myosin cross-linking** — TRUE; this is the biochemical mechanism 4. **Complete resolution by 48–72 hours in all conditions** — FALSE; resolution is highly variable and depends on temperature, humidity, and decomposition rate