Child Abuse: Understanding the Biomechanics of Rib Fractures in Infants

Abstract

There are some general assumptions made by forensic paediatricians and pathologists about how infants in child abuse cases suffer fractured ribs; the main assumption being that rib fractures are resultant from ‘shaken baby syndrome’. There have been many studies on the biomechanics of rib fractures in adults and the different modes through which these occur, but there has been no scientific research conducted on the biomechanics of rib fractures in infants or children. There are two main aims to this study; firstly, to assess the biomechanical properties of immature piglet ribs and compare these results with published literature on adult pig ribs and secondly, to compare and contrast the fracture patterns of immature piglet ribs in three categories: dry, frozen then thawed, and fresh. Piglet ribs were taken from still born or day-old piglets and tested in the three different categories and two different protocols for stress, strain, modulus, and maximum load measurements. Scanning Electron Microscopy and micro-CT scanning were the imaging techniques used to examine morphological differences between the three categories. It was found that the dry samples had catastrophic breaks that followed a straight and then oblique fracture pattern, whereas the fractures observed in the frozen and thawed samples were straight, incomplete fractures. Fresh samples did not fracture. Statistically significant differences were found between each of the three categories; in particular the frozen then thawed ribs produced greater biomechanical results than the fresh ribs which were expected to be similar in response. This suggests that using freezing as a storage method significantly alters the biomechanical analysis The present study seriously challenges the current dogma on shaken baby syndrome in the literature, and suggests that rib fractures do not occur during compressive loading of the rib cage in infants due to the very high plasticity and partial bony development.