Estimation of the post-mortem interval; added value of mechanical excitability of human skeletal muscle.

Estimation of the post-mortem interval (PMI) is mainly based on the state of body cooling, post-mortem lividity (livor mortis) and post-mortem muscle stiffness (rigor mortis). However, the time span of development of these post-mortem phenomena are influenced by a variety of factors concerning the body of the deceased and the environment in which the body is found. Subsequently, this leads to a substantial spread in upper and lower limits of PMI based on determination of the state of these phenomena. Moreover, interpretation of post-mortem phenomena like lividity, rigor and interpretation of the correction factor for Henssge's nomogram is subjective. For this reason, PMI estimations are often broad, possibly too broad to be helpful for answering questions which are relevant for the criminal investigation. Therefore, combining the outcome of different methods for estimating the PMI, the so-called compound method, is recommended. Supravital muscle reaction by mechanical stimulation of skeletal muscle is a less known aspect of the compound method. Here we present a series of cases series in which supravital muscle reaction contributed to a more precise estimation of the PMI.

Technical note: Practical application of post-mortem mechanical stimulation of skeletal muscle, a field study.

BACKGROUND: Estimation of the post-mortem interval (PMI) is a crucial aspect in crime scene investigation. PMI is defined as the time between the moment of death and the moment of finding the dead body. A combination of methods for estimating the PMI in forensic casework is internationally mostly used. Supravital muscle reaction (SMR) is one of those methods. SMR is an idiomuscular contraction and can be provoked by mechanical stimulation. OBJECTIVES: A field study was carried out with the aim to investigate whether a reflex hammer can be used as tool for triggering an idiomuscular contraction and, furthermore, to determine if a learning period has to be taken into account by a forensic physician for appropriate application of a reflex hammer to trigger SMR. METHODS: From January 2017 to January 2022, four forensic physicians used this SMR by mechanically stimulating the musculus brachioradialis and musculus biceps brachii. In total, 332 cases were included with a PMI less than 24 h. The cases were divided in chronological clusters of 20 cases. The ratio of the number of positive SMR versus the total number stimulations per forensic physician was used as a measure of accuracy of a reflex hammer for triggering SMR. The distribution of the data was analyzed by comparing the clusters in chronological order to assess whether a learning curve applies. RESULTS: In 55.7%, a muscle reaction could be provoked by mechanical stimulation. Comparable outcome of SMR between the participating physicians was observed after 40 stimulations. CONCLUSION: A reflex hammer is usable for provoking SMR. A learning period has to be taken in to account during the first forty cases per forensic physician.