Modeling of inflicted head injury by shaking trauma in children: what can we learn? : Part II: A systematic review of mathematical and physical models

Modeling of inflicted head injury by shaking trauma in children: what can we learn? : Update to parts I&II: A systematic review of animal, mathematical and physical models

Inflicted shaking trauma can cause injury in infants, but exact injury mechanisms remain unclear. Controversy exists, particularly in courts, whether additional causes such as impact are required to produce injuries found in cases of (suspected) shaking. Publication rates of studies on animal and biomechanical models of inflicted head injury by shaking trauma (IHI-ST) in infants continue rising. Dissention on the topic, combined with its legal relevance, makes maintaining an up-to-date, clear and accessible overview of the current knowledge-base on IHI-ST essential. The current work reviews recent (2017-2023) studies using models of IHI-ST, serving as an update to two previously published reviews. A systematic review was conducted in Scopus and PubMed for articles using animal, physical and mathematical models for IHI-ST. Using the PRISMA methodology, two researchers independently screened the publications. Two, five, and ten publications were included on animal, physical, and mathematical models of IHI-ST, respectively. Both animal model studies used rodents. It is unknown to what degree these can accurately represent IHI-ST. Physical models were used mostly to investigate gross head-kinematics during shaking. Most mathematical models were used to study local effects on the eye and the head's internal structures. All injury thresholds and material properties used were based on scaled adult or animal data. Shaking motions used as inputs for animal, physical and mathematical models were mostly greatly simplified. Future research should focus on using more accurate shaking inputs for models, and on developing or and validating accurate injury thresholds applicable for shaking.

Inflicted head-injury by shaking-trauma in infants: the importance of spatiotemporal variations of the head's rotation center

Inflicted head injury by shaking trauma (IHI-ST) in infants is a type of abusive head trauma often simulated computationally to investigate causalities between violent shaking and injury. This is commonly done with the head's rotation center kept fixed over time. However, due to the flexibility of the infant's neck and the external shaking motion imposed by the perpetrator it is unlikely that the rotation center is static. Using a test-dummy, shaken by volunteers, we demonstrated experimentally that the location of the head's rotation center moves considerably over time. We further showed that implementation of a spatiotemporal-varying rotation center in an improved kinematic model resulted in strongly improved replication of shaking compared to existing methods. Hence, we stress that the validity of current infant shaking injury risk assessments and the injury thresholds on which these assessments are based, both often used in court cases, should be re-evaluated.

Animal models of pediatric abusive head trauma

BACKGROUND

Abusive head trauma (AHT), previously known as the shaken baby syndrome, is a severe and potentially fatal form of traumatic brain injury in infant children who have been shaken, and sometimes also sustained an additional head impact. The clinical and autopsy findings in AHT are not pathognomonic and, due to frequent obfuscation by perpetrators, the circumstances surrounding the alleged abuse are often unclear. The concept has evolved that the finding of the combination of subdural hemorrhage, brain injury, and retinal hemorrhages ("the triad") is the result of shaking of an infant ("shaken baby syndrome") and has led to the ongoing controversy whether shaking alone is able to generate sufficient force to produce these lesions.

OBJECTIVE

In an attempt to investigate whether shaking can engender this lesion triad, animal models have been developed in laboratory rodents and domestic animal species. This review assesses the utility of these animal models to reliably reproduce human AHT pathology and evaluate the effects of shaking on the immature brain.

RESULTS

Due largely to irreconcilable anatomic species differences between these animal brains and human infants, and a lack of resemblance of the experimental head shaking induced by mechanical devices to real-world human neurotrauma, no animal model has been able to reliably reproduce the full range of neuropathologic AHT changes.

CONCLUSION

Some animal models can simulate specific brain and ophthalmic lesions found in human AHT cases and provide useful information on their pathogenesis. Moreover, one animal model demonstrated that shaking of a freely mobile head, without an additional head impact, could be lethal, and produce significant brain pathology.

Thrombosis is not a marker of bridging vein rupture in infants with alleged abusive head trauma

Aim

Thrombosis of bridging veins has been suggested to be a marker of bridging vein rupture, and thus AHT, in infants with subdural haematoma.

Methods

This is a non‐systematic review based on Pubmed search, secondary reference tracking and authors’ own article collections.

Results

Radiological studies asserting that imaging signs of cortical vein thrombosis were indicative of traumatic bridging vein rupture were unreliable as they lacked pathological verification of either thrombosis or rupture, and paid little regard to medical conditions other than trauma. Autopsy attempts at confirmation of ruptured bridging veins as the origin of SDH were fraught with difficulty. Moreover, microscopic anatomy demonstrated alternative non‐traumatic sources of a clot in or around bridging veins. Objective pathological observations did not support the hypothesis that a radiological finding of bridging vein thrombosis was the result of traumatic rupture by AHT. No biomechanical models have produced reliable and reproducible data to demonstrate that shaking alone can be a cause of bridging vein rupture.

Conclusion

There is no conclusive evidence supporting the hypothesis that diagnostic imaging showing thrombosed bridging veins in infants correlates with bridging vein rupture. Hence, there is no literature support for the use of thrombosis as a marker for AHT.

Violent Infant Surrogate Shaking: Continuous High-Magnitude Centripetal Force and Abrupt Shift in Tangential Acceleration May Explain High Risk of Subdural Hemorrhage

Violent shaking is believed to be a common mechanism of injury in pediatric abusive head trauma. Typical intracranial injuries include subdural and retinal hemorrhages. Using a laboratory surrogate model we conducted experiments evaluating the head motion patterns that may occur in violent shaking. An anthropomorphic test device (ATD; Q0 dummy) matching an infant of 3.5 kg was assembled. The head interior was equipped with accelerometers enabling assessment of three-axial accelerations. Fifteen volunteers were asked to shake the surrogate vigorously holding a firm grip around the torso. We observed the volunteers performing manual shaking of the surrogate at a median duration of 15.5 sec (range 5-54 sec). Typical acceleration/deceleration patterns were produced after 2-3 shakes with a steady-state shaking motion at a pace of 4-6 cycles (back and forth) per second. Mean peak sagittal tangential accelerations at the vertex were 45.7g (range 14.2-105.1g). The acceleration component in the orthogonal direction, the radial acceleration, fluctuated around a negative mean of more than 4g showing that the surrogate head was continuously subjected to centripetal forces caused by rotations. This surrogate experiment showed that violent shaking may induce high peak tangential accelerations and concomitantly a continuous high-magnitude centripetal force. We hypothesize that the latter component may cause increased pressure in the subdural compartment in the cranial roof and may cause constant compression of the brain and possibly increased stretching or shearing of the bridging veins. This may contribute to the mechanism accountable for subdural hematoma in abusive head trauma.

Parenchymal brain injuries in abusive head trauma

The consequences of abusive head trauma (AHT) can be devastating for both the individual child and for wider society. Death is undoubtedly a very real possibility, but even for those children who survive, there is often very significant morbidity with the potential for gross motor and cognitive impairment, behavioural problems, blindness and epilepsy, which can greatly affect their quality of life. Caring for such children places a vast financial and infrastructural burden on society that frequently extends well into adulthood. While few struggle to have any sympathy for the perpetrator, frequently the infant's father, it should be noted that a single solitary and momentary loss of complete control can have horrific and unforeseen consequences. A number of papers within this edition describe features of AHT and include descriptions of skull fractures and extra-axial haemorrhage, along with mimics of such phenomena. However, in this review we concentrate our attention on the myriad of parenchymal findings that can occur. Such parenchymal injuries include hypoxic-ischaemic damage, clefts, contusion and focal haemorrhage. We offer our perspectives on current thinking on these entities and put them in the context of the immensely important question - how do we recognise abusive head trauma?

Neuroendoscopic Approach of a Massive Bilateral Chronic Subdural Hematoma in a Child Using a Single Burr Hole

There are several treatment modalities for the management of subdural fluid collection in infants, such as fontanelle puncture and drainage, burr hole irrigation, and subduroperitoneal shunt. This report describes the case of a girl born with congenital neurological impairment due to severe injury of the brain with unknown etiology. At five months of age, she suffered from head trauma and developed somnolence after three days and was diagnosed with a bilateral massive chronic subdural hematoma. Normal fundoscopy did not confirm the non-accidental head trauma. Neuroendoscopy using a single burr hole was performed and complete drainage was achieved. Arachnoid tearing was observed during the procedure. Postoperatively, the patient showed clinical improvement, and brain expansion was observed after one month. The main advantages of neuroendoscopy for bilateral massive chronic subdural hematoma are accurate visualization of the space, minimal invasiveness, and treatment of both sides with reliable drainage control.

Thresholds for the assessment of inflicted head injury by shaking trauma in infants: a systematic review

In order to investigate potential causal relations between the shaking of infants and injuries, biomechanical studies compare brain and skull dynamic behavior during shaking to injury thresholds. However, performing shaking tolerance research on infants, either in vivo or ex vivo, is extremely difficult, if not impossible. Therefore, infant injury thresholds are usually estimated by scaling or extrapolating adult or animal data obtained from crash tests or whiplash experiments. However, it is doubtful whether such data accurately matches the biomechanics of shaking in an infant. Hence some thresholds may be inappropriate to be used for the assessment of inflicted head injury by shaking trauma in infants. A systematic literature review was conducted to 1) provide an overview of existing thresholds for head- and neck injuries related to violent shaking, and 2) to identify and discuss which thresholds have been used or could be used for the assessment of inflicted head injury by shaking trauma in infants. Key findings: The majority of studies establishing or proposing injury thresholds were found to be based on loading cycle durations and loading cycle repetitions that did not resemble those occurring during shaking, or had experimental conditions that were insufficiently documented in order to evaluate the applicability of such thresholds. Injury thresholds that were applied in studies aimed at assessing whether an injury could occur under certain shaking conditions were all based on experiments that did not properly replicate the loading characteristics of shaking. Somewhat validated threshold scaling methods only exist for scaling concussive injury thresholds from adult primate to adult human. Scaling methods that have been used for scaling other injuries, or for scaling adult injury thresholds to infants were not validated. There is a clear and urgent need for new injury thresholds established by accurately replicating the loading characteristics of shaking.