Rigor Mortis

Rigor mortis literally translates to “stiffness of death“.

Nysten in 1811 is credited with being the first person to use rigor mortis to determine the time of death. He is the first to show postmortem rigidity in a criminal inquiry. It’s a physical change that affects all muscles in animals and humans who have just died. When this happens, it means that fatalities happened during the last 2-4 hours.

Rigor Mortis is a Third stage of death. It’s a chemical process that causes muscle fibres to stiffen in flexion position by forming a stable combination of adenosine and myosin and occurs periodically.

Mechanism:

A variety of metabolic processes occur inside the skeletal and cardiac muscle fibres throughout the body shortly after death. Specifically, the chemical source of energy for muscular contraction, adenosine triphosphate (ATP), continues to be used by muscle cells, leading in the creation of cross-bridges between myosin and actin fibres. When you die, though, your body stops producing fresh ATP. Because ATP is necessary for the dissociation of actin and myosin fibres and the resulting muscle relaxation, relaxation is no longer possible after the ATP supply is depleted. As a result, the muscle fibres are unable to relax and stay in a constant state of contraction. As a result of the absence of extra ATP, the muscle fibres stay in a constant state of contraction, unable to relax. When a result, as these processes take place after death, the body’s muscles will grow progressively stiff until all of the ATP has been spent. Rigor mortis is the term for postmortem muscular stiffness. Rigor mortis will last until the myosin and actin filaments are fragmented, which can be done by physical manipulation or early decomposition.

The muscles become limp or flaccid shortly after death. The muscles begin to stiffen within the first hour following death. Rigor mortis occurs simultaneously in all muscles. Because muscle parts differ in size and mass, rigor mortis manifests itself first in the smaller muscles, such as the jaw and fingers. Within 3 hours, rigor mortis nearly spread in all muscles of body.

The jaw, arms, and eventually the legs are straightened out of the flexion posture and the resistance is measured to determine rigor.
Because rigor mortis is a chemical reaction, the pace of development varies greatly depending on the environment, the size of the individual, and the person’s state upon death.

Rigor mortis develops and fades faster in instances of weariness or protracted sickness, whereas it develops slowly in cases of suffocation, apoplexy, or neurological disorders. Strychnine and other spinal toxins have a faster start and a longer duration.

The muscles become limp and flaccid as the rigour mortis progresses, and they do not respond to mechanical or electrical stimulation. The indications of decomposition grow increasingly visible on the body, and the corpse becomes completely relaxed and flaccid, allowing it to be placed in any position or posture.

Here are some more rigour mortis facts:

✔ At 70°F–75°F, muscles stiffen about 1–3 hours after death, and grow completely after 9–12 hours.

✔ A high fever or a high ambient temperature can hasten the onset of rigidity.

✔ If the deceased was engaged in vigorous physical activity just before death, rigour mortis will develop more quickly.

✔ Rigor mortis is initially noticed in the jaw, then the face, and finally the upper and lower extremities. To feel if the linked joints are movable, the examiner must first check the mouth, then the arms, and finally the legs.

✔ When the jaw, elbow, and knee joints are immobile, the body is said to be in total (full) rigidity.

✔ At 70°F–75°F, the body will stay stiff for 24–36 hours until the muscles begin to relax, generally in the same order that they tightened.

✔ In lower temperatures, rigor is slowed, whereas in warmer temperatures, it is accelerated.

✔ When the body stiffens, it stays that way until the rigour passes or the joint is physically moved, breaking the rigidity (or decomposition occurs).

✔ The posture of a body in complete rigour might reveal whether or not the body has been moved after death.

If a body has been moved after death, seeing rigour mortis might be beneficial.

Rigor Mortis First appears in:

The rigour mortis takes a predictable path. It begins with the muscles of the eyelids, then moves on to the muscles of the back of the neck and lower jaw, the front of the neck, the face, the chest, and the upper extremities, and finally to the muscles of the belly and lower extremities. It disappears in the same order in which it appeared. Rigor mortis is most severe in the tiny muscles of the fingers and toes.

Rigor Mortis is not Appear in:

Rigor mortis does not develop in an immature foetus under the age of 7 months. In infants and the elderly, the onset is gradual but noticeable, but in adults, it is slow but noticeable.

Effect of Temperature on Rigor Mortis:

When the environment is dry and cold, the onset is gradual but the length is greater than when the atmosphere is hot and humid, when the onset is quick and the duration is shorter. Rigor mortis occurs early and fades late in case of drowning.

Rigor mortis can be simulated by the following conditions:

1. Heat Stiffening:

When the body is exposed to temperatures exceeding 50°C, muscle protein coagulates, causing muscles to become rigid and stiff, simulating rigour mortis. Due to the extreme heat observed in burns, the body adopts a ‘pugilistic attitude,’ with lower limbs and arms contracted and fists clenched. The whole body has been burned. It is caused by muscular shortening as a result of heat.

2. Cold Stiffening:

When the body is exposed to severe cold, solidification of body fat causes muscular stiffness, resulting in cold stiffening. Due to cold exposure, the skin folds around the neck of babies may resemble ligature marks.

3. Cadaveric Spasm:

Sometimes, after death, the muscles of the body go straight into a state of contraction without going through the typical early phase of relaxation. This is known as cadaveric spasm or instantaneous rigour. It is usually restricted to a specific set of muscles rather than affecting the entire body. This occurs when death occurs at a period of intense physical activity and mental excitement inside the body. It is prevalent in scenarios such as combat, drowning, strangling, suicide, and so forth. The actual cause of cadaveric spasm is unknown, however increased neuronal discharge into a specific group of muscles before to death has been suggested as one of the causes.

Cadaveric spasm has high medical-legal importance since the presence of a weapon, hair, weeds, clothing fragments, and other items gripped in the hands may point to the cause of death. Cadaveric spasm is a pre-mortem condition that cannot be induced after death. Weapons held in cadaveric spasm-infected hands can only be withdrawn with extreme difficulty.

References

Reddy KS. The Essentials of Forensic medicine and Toxicology. 26th ed. Hyderabad: K. Saguna Devi; 2007. pp. 130

Parikh CK. Parikh’s textbook of medical jurisprudence, forensic medicine and toxicology. 6th ed. Delhi: CBS Publishers; 1999. pp. 3–16. 

Shivpoojan Kori. Time since Death from Rigor Mortis: Forensic Prospective , Volume – 9 Issue 5- June 2018, DOI: 10.19080/JFSCI.2018.09.555771

Sharma R.K. Concise Textbook of Forensic Medicine & Toxicology, pp. 48