Estimation of the time since death: post-mortem contractions of human skeletal muscles following mechanical stimulation (idiomuscular contraction).

The mechanically stimulated idiomuscular contraction of skeletal muscles is part of the widely used compound method for death time estimation and therefore represents an item of high relevance and practicability in forensic case work. However, data on the topic are scarce and inconsistent and the currently reported maximum time span for the occurrence of the phenomenon until 13 h post-mortem (hpm) is based on a single case report from the beginning of the twentieth century. Therefore, idiomuscular contraction following mechanical stimulation has been investigated in skeletal muscles of 270 cases with assured time of death at defined post-mortem time points between 7 and 15 hpm. Of all investigated cases, 45 (16.7%) showed a positive reaction with a preponderance of cases of sudden death. Our investigations confirmed the upper time limit of 13 hpm up until idiomuscular contraction could be stimulated. With every hour of the post-mortem interval, a 0.61-fold decrease of the phenomenon's occurrence was observed (95%CI, 0.52-0.72; p < 0.001). Furthermore, several parameters showed significant correlations with the likelihood of the phenomenon's occurrence, namely stimulation of upper arm as opposed to the thigh (p < 0.001), gender (p = 0.017), and BMI (p < 0.001). These findings for the first time give reliable evidence of a post-mortem time limit of mechanically stimulated idiomuscular contraction and therefore contribute to the future application of the method in forensic case work.