Mechanistic hypothesis for eye injury in infant shaking : An experimental and computational study

Ophthalmological lesions in shaken baby syndrome: a retrospective analysis of 133 consecutive cases (1992-2018)

INTRODUCTION

Shaken Baby Syndrome (SBS) is a non-accidental head trauma in which shaking causes cranio-cerebral lesions. Shaking can lead to ophthalmologic lesions such as retinal hemorrhage (RH). The aim of the present study was to compare our long-term results in to the literature data.

PATIENTS AND METHODS

This study was a single-center retrospective descriptive analysis of 133 consecutive SBS cases (1992 - 2018). Only seniors in ophthalmology were authorized to perform these examinations. We studied type of lesion (retinal, intra-vitreal, papilledema), location (uni- or bi-lateral), and correlation with gender and age. Infants with a traumatic context without suspicion of child abuse were excluded.

RESULTS

Mean age at diagnosis was 131 days (range, 14 days - 10 months). Boys accounted for 72.2% of the population. The prevalence of ophthalmologic lesions was 70.3%. 94.4% were RH; intra-vitreous hemorrhage (6.7%) and papilledema (11.1%) were less frequent. Lesions were bilateral in 81.1% of cases. Retinal lesions were classified in terms of location. Macular involvement was diagnosed in 8.2% of cases. 18.8% of retinal lesions could not be classified because of lack of precision in the ophthalmology report. The prevalence of ophthalmic lesions was higher for children aged over 6 months: 80%.

CONCLUSION

This series highlighted a high rate of ophthalmic lesions in SBS, with a high rate of bilateral involvement. RH was the most frequent lesion. RH in a context of subdural hematoma is a strong argument in favor of SBS. The forensic implications are that rigorous ophthalmologic examination by a senior practitioner is mandatory.

Charting the Globe: How Technologies Have Affected Our Understanding of Retinal Findings in Abusive Head Trauma/Shaken Baby Syndrome

Purpose: Ocular findings such as retinal hemorrhages are common in abusive head trauma (AHT). Binocular indirect ophthalmoscopy has been the standard for assessing the eyes of children who are victims of AHT. However, technological advances have changed our understanding of retinal findings in AHT.Methods: Literature review on AHT - retinal findings, imaging technologies, models of representation, and telemedicine applications.Results: Many studies suggest vitreoretinal traction from repetitive acceleration-deceleration shearing forces during shaking plays an important role in the development of retinal findings in AHT. This is further supported by different imaging modalities [optical coherence tomography (OCT); magnetic resonance imaging (MRI); fluorescein angiography (FA)] and models of representation (animal and mechanical models; finite element analysis).Conclusion: Emerging technologies have augmented our diagnostic abilities, enhanced our understanding regarding the pathophysiology of retinal findings, and strengthened the link between vitreoretinal traction and ocular pathology in AHT. Telemedicine is also starting to play an important role in AHT.

Modeling Hypertension as a Contributor to Retinal Hemorrhaging from Abusive Head Trauma

Retinal hemorrhaging (RH) is indicative and prevalent in abusive head trauma (AHT)—yet the direct cause of the RH from AHT is unknown. Our hypothesis is that RH in AHT is the combination of shaking forces and hypertension. This combination of effects explains why RH is not normally observed in common childhood accidents but is nearly exclusively observed in AHT. An experimental model using porcine eyes was designed to ascertain the required pressure change for sudden RH and, via a computer model, the subsequent stress increase in blood vessels. The porcine eyes were cannulated via the maxillary artery and pressurized until perfusion and RH were observed. Fluid was injected into the head with a computer-controlled continuous flow syringe pump; video of the fundus was recorded during perfusion; and the pressure of the fluid entering the eye was recorded as well. A computer model was created in COMSOL to simulate loading from hypertension, shaking, and the combination of the forces. This model was validated via experimental data collected from the porcine model. It was found that hypertension or shaking alone did not cause an increase in stress required to cause RH. But when the loading of shaking and hypertension was combined, as would occur in AHT, the stress increases were greater than those extrapolated from the porcine model and would cause RH.

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

Various types of complex biomechanical models have been published in the literature to better understand processes related to inflicted head injury by shaking trauma (IHI-ST) in infants. In this systematic review, a comprehensive overview of these models is provided. A systematic review was performed in MEDLINE and Scopus for articles using physical (e.g. dolls) and mathematical (e.g. computer simulations) biomechanical models for IHI-ST. After deduplication, the studies were independently screened by two researchers using PRISMA methodology and data extracted from the papers is represented in a “7-steps description”, addressing the different processes occurring during IHI-ST. Eleven papers on physical models and 23 papers on mathematical models were included after the selection process. In both categories, some models focus on describing gross head kinematics during IHI-ST events, while others address the behavior of internal head- and eye structures in various levels of detail. In virtually all physical and mathematical models analyzed, injury thresholds are derived from scaled non-infant data. Studies focusing on head kinematics often use injury thresholds derived from impact studies. It remains unclear to what extent these thresholds reflect the failure thresholds of infant biological material. Future research should therefore focus on investigating failure thresholds of infant biological material as well as on possible alternative injury mechanism and alternative injury criteria for IHI-ST.

PATHOLOGY OF PERIMACULAR FOLDS DUE TO VITREORETINAL TRACTION IN ABUSIVE HEAD TRAUMA

PURPOSE

To demonstrate vitreoretinal traction as a mechanism for perimacular folds in abusive head trauma.

METHODS

We performed gross and histopathologic examination of eyes of children with suspected abusive head trauma and identified those with typical perimacular folds. Information was collected regarding the incident that led to the child's death and systemic manifestations noted at autopsy. Eyes were prepared in a fashion that allowed for demonstration of the vitreoretinal interface.

RESULTS

Ten eyes of five patients (2-13 months) were examined. All patients had systemic manifestations of abusive trauma including intracranial injury. All cases provided evidence of vitreoretinal traction producing perimacular folds. Condensed vitreous was seen attached to the apices of the retinal folds, and the detached internal limiting membrane comprising the inner surfaces of the schisis cavity. Four cases showed severe bilateral multilayered symmetric retinal hemorrhages extending to the ora serrata. All cases showed optic nerve sheath subdural hemorrhage and subarachnoid hemorrhage. Orbital hemorrhage was unilateral in two cases and bilateral in three cases. Four cases showed orbital fat hemorrhage. One case showed extraocular muscle sheath and cranial nerve sheath hemorrhage. Two cases showed juxtapapillary intrascleral hemorrhage.

CONCLUSION

Vitreoretinal traction is the likely mechanism of perimacular folds in abusive head trauma.

Update on injury mechanisms in abusive head trauma--shaken baby syndrome

Violently shaking a baby leads to clinical presentations ranging from seizures to cardiopulmonary arrest. The main injuries sustained are retinal hemorrhages, subdural hemorrhages, and sometimes fractures and spine injury. It is important to have a global view of the injuries sustained by the infant to correctly discuss the biomechanical aspects of abusive head trauma. Recent works based on finite element models have shown that whiplash-shaking alone is enough to generate vitreo-retinal traction leading to retinal hemorrhage and to cause the rupture of bridging veins leading to subdural hemorrhage. We will review the main papers dealing with the mechanisms of shaken baby syndrome and present the most relevant hypothesis concerning the biomechanical aspects of injuries related to shaken baby syndrome.

Retinal hemorrhage in abusive head trauma

Retinal hemorrhage is a cardinal manifestation of abusive head trauma. Over the 30 years since the recognition of this association, multiple streams of research, including clinical, postmortem, animal, mechanical, and finite element studies, have created a robust understanding of the clinical features, diagnostic importance, differential diagnosis, and pathophysiology of this finding. The importance of describing the hemorrhages adequately is paramount in ensuring accurate and complete differential diagnosis. Challenges remain in developing models that adequately replicate the forces required to cause retinal hemorrhage in children. Although questions, such as the effect of increased intracranial pressure, hypoxia, and impact, are still raised (particularly in court), clinicians can confidently rely on a large and solid evidence base when assessing the implications of retinal hemorrhage in children with concern of possible child abuse.

The eye examination in the evaluation of child abuse

Retinal hemorrhage is an important indicator of possible abusive head trauma, but it is also found in a number of other conditions. Distinguishing the type, number, and pattern of retinal hemorrhages may be helpful in establishing a differential diagnosis. Identification of ocular abnormalities requires a full retinal examination by an ophthalmologist using indirect ophthalmoscopy through a pupil that has been pharmacologically dilated. At autopsy, removal of the eyes and orbital tissues may also reveal abnormalities not discovered before death. In previously well young children who experience unexpected apparent life-threatening events with no obvious cause, children with head trauma that results in significant intracranial hemorrhage and brain injury, victims of abusive head trauma, and children with unexplained death, premortem clinical eye examination and postmortem examination of the eyes and orbits may be helpful in detecting abnormalities that can help establish the underlying etiology.

Finite element model of ocular injury in abusive head trauma

PURPOSE

To develop a finite element analysis of the eye and orbit that can be subjected to virtual shaking forces.

METHODS

LS-DYNA computer software was used to design a finite element model of the human infant eye, including orbit, fat, sclera, retina, vitreous, and muscles. The orbit was modeled as a rigid solid; the sclera and retina as elastic shells; the vitreous as viscoelastic solid or Newtonian fluid; and fat as elastic or viscoelastic solid. Muscles were modeled as spring-damper systems. Orbit-fat, fat-sclera, sclera-retina, and vitreous nodes-retina interfaces were defined with the use of the tied surface-surface function in LS-DYNA. The model was subjected to angular acceleration pulses obtained from shaking tests of a biofidelic doll (Aprica 2.5 kg dummy). Parametric studies were conducted to evaluate the effect of varying the material properties of vitreous/fat on maximum stress and stress distribution.

RESULTS

With the vitreous modeled as a Newtonian fluid, the repeated acceleration-deceleration oscillatory motion characteristic of abusive head trauma (AHT) causes cumulative increases in the forces experienced at the vitreoretinal interface. Under these vitreous conditions, retinal stress maximums occur at the posterior pole and peripheral retina, where AHT retinal hemorrhage is most often found.

CONCLUSIONS

Our model offers an improvement on dummy and animal models in allowing analysis of the effect of shaking on ocular tissues. It can be used under certain material conditions to demonstrate progressive "stacking" of intraocular stresses in locations corresponding to typical AHT injury patterns, allowing a better understanding of the mechanisms of retinal hemorrhage patterns.

Computer modelling study of the mechanism of optic nerve injury in blunt trauma

AIM

The potential causes of the optic nerve injury as a result of blunt object trauma, were investigated using a computer model.

METHODS

A finite element model of the eye, the optic nerve, and the orbit with its content was constructed to simulate blunt object trauma. We used a model of the first phalanx of the index finger to represent the blunt body. The trauma was simulated by impacting the blunt body at the surface between the globe and the orbital wall at velocities between 2-5 m/s, and allowing it to penetrate 4-10 mm below the orbital rim.

RESULTS

The impact caused rotations of the globe of up to 5000 degrees /s, lateral velocities of up to 1 m/s, and intraocular pressures (IOP) of over 300 mm Hg. The main stress concentration was observed at the insertion of the nerve into the sclera, at the side opposite to the impact.

CONCLUSIONS

The results suggest that the most likely mechanisms of injury are rapid rotation and lateral translation of the globe, as well as a dramatic rise in the IOP. The strains calculated in the study should be sufficiently high to cause axonal damage and even the avulsion of the nerve. Finite element computer modelling has therefore provided important insights into a clinical scenario that cannot be replicated in human or animal experiments.