Forensic Medicine: Thanatology, Injury and Medico-legal Reasoning
Forensic medicine tests your ability to reason from postmortem findings to cause, mechanism and manner of death, and to apply the law to clinical situations. Thanatology, asphyxial deaths, wound ballistics, poisoning and identification are the recurring themes.
Core rules
- Rigor mortis begins in 1-2 hours, becomes complete by about 12 hours and resolves by 24-36 hours depending on temperature.
- Livor mortis appears within 20-30 minutes and fixes by 6-8 hours.
- Hanging produces an oblique, incomplete ligature mark above the thyroid cartilage, with dribbling of saliva; ligature strangulation produces a horizontal, complete mark below the cartilage, often with a fractured hyoid.
- Diatoms recovered from bone marrow indicate antemortem drowning.
- Manner of death (natural, accident, suicide, homicide, undetermined) is distinct from cause and from mechanism.
Worked example
A body is found suspended with the feet touching the floor. The ligature mark is oblique, non-continuous and high in the neck; there are petechiae but the hyoid is intact. This is consistent with suicidal hanging. If the mark were horizontal, continuous and low, with a fractured hyoid and signs of a struggle, ligature strangulation with a homicidal manner would be more likely. The cause of death is asphyxia; the mechanism is hypoxia; the manner is suicide.
Traps
- Confusing cadaveric spasm with rigor mortis; the former is instantaneous and involves a specific muscle group.
- Missing the lucid interval of an extradural haematoma when attributing death timing.
- Recording cause, mechanism and manner as a single item.