Rigor Mortis (Stiffness of Death)
Forensic Pathology: Post-Mortem Changes
1. Biochemical Basis
Rigor mortis is caused by the depletion of Adenosine Triphosphate (ATP) in muscle cells after death. Without ATP, the myosin heads cannot detach from the actin filaments, leading to a locked, contracted state of the muscles.
2. Timeline (Nysten’s Law)
Rigor typically follows Nysten’s Law, appearing first in smaller muscle groups (jaw, face) and progressing downwards to larger muscle groups (trunk, extremities).
| Stage | Approximate Timing |
|---|---|
| Onset | 2–4 hours post-mortem. |
| Fully Developed | 12 hours post-mortem. |
| Resolution | 24–36 hours (due to autolysis). |
3. Forensic High-Yield Pearls
- “Breaking” Rigor: If rigor is manually broken (e.g., straightening a stiffened joint), it will not reform. This is a vital clue in assessing if a body has been moved or repositioned post-mortem.
- Cadaveric Spasm: A rare, instantaneous onset of rigor that occurs at the moment of death, usually associated with extreme emotional stress or brain injury. Unlike standard rigor, it cannot be broken.
- Influencing Factors:
- Heat: Accelerates the onset and resolution of rigor.
- Cold: Delays the onset and extends the duration.
- Physical Activity: Pre-mortem exertion (e.g., struggle) leads to rapid depletion of ATP, causing an early onset.