The use of kidney biomechanics in forensic pathology.

Forensic tissue mechanics has emerged as a promising complementary approach for post-mortem interval (PMI) estimation, particularly for intermediate and later post-mortem phases where temperature-based methods become unreliable. However, human kidney tissue has not yet been systematically investigated within this framework. This study aimed to characterize the rheological properties of human kidney tissue under standardized post-mortem conditions and assess their relationship with PMI and potential confounding factors. Kidney samples from 49 cadavers (36 male, 13 female; mean age 65 ± 16 years; PMI range 42-518 h) were collected during forensic autopsies. Circular cylindrical tissue samples were subjected to oscillatory shear rheometry to determine storage modulus (G'), loss modulus (G"), and complex shear modulus (G*). Histological examination and statistical analyses including univariable and multivariable regression were performed. G' and G* showed significant negative correlations with PMI (G': r = -0.379, p = 0.010; G*: r = -0.374, p = 0.012), indicating progressive post-mortem tissue softening. For the 250-hour PMI threshold, G' yielded a positive likelihood ratio of 9.9 (sensitivity = 35.3%, specificity = 96.4%; cut-off value = 1251 Pa). PMI-related biomechanical changes were independent of age at death, sex, kidney weight, gross renal pathology, and cause of death, suggesting potential diagnostic utility as part of a multi-organ biomechanical framework. Human kidney tissue exhibits characteristic post-mortem biomechanical alterations associated with PMI but no other relevant confounders. The observed rheological changes support kidney biomechanics as a valuable addition to a multi-organ framework for forensic PMI estimation during intermediate and later post-mortem intervals.