Potential for head injuries in infants from low-height falls: Laboratory investigation

Object. Falls are the most common accident scenario in young children as well as the most common history provided in child abuse cases. Understanding the biomechanics of falls provides clinicians with objective data to aid in their diagnosis of accidental or inflicted trauma. The objective of this study was to determine impact forces and angular accelerations associated with low-height falls in infants. Methods. An instrumented anthropomorphic infant surrogate was created to measure the forces and 3D angular accelerations associated with falls from low heights (0.3–0.9 m) onto a mattress, carpet pad, or concrete. Results. Although height significantly increased peak angular acceleration (αp), change in peak-to-peak angular velocity, time duration associated with the change in velocity, and peak impact force (Fp) for head-first drops onto a carpet pad or concrete, none of these variables were significantly affected by height when dropped onto a mattress. The αp was not significantly different for drops onto a carpet pad and concrete from 0.6 or 0.9 m due to compression of the carpet pad. Surprisingly, sagittal αp was equaled or surpassed by axial αp. Conclusions. These are the first 3D angular acceleration and impact force data available for head impact in infants from low-height falls. A future study involving a computational model of the infant head will use the loads measured in this study to predict the probability of occipital skull fracture on impact from head-first low-height falls. Together, these studies will provide data that will aid clinicians in the evaluation of accidental and inflicted head injuries, and will contribute to the design of safer environments for children. (DOI: 10.3171/PED.2008.2.11.321

Finite Element Model Predictions of Intracranial Hemorrhage From Non-impact, Rapid Head Rotations in the Piglet

Clinicians are charged with the significant task of distinguishing between accidental and inflicted head trauma. Oftentimes this distinction is straightforward, but many times probabilities of injuries from accidental scenarios are unknown making the differential diagnosis difficult. For example, it is unknown whether intracranial hemorrhage (IH) can occur at a location other than a focal contact site following a low height fall. To create a foundation for predicting regional IH in infants, we sought to identify the biomechanical response and injury threshold best able to predict IH in 3–5 day old piglets. First, finite element (FE) model simulations of in situ animal studies were performed to ascertain the optimal representation of the pia-arachnoid complex, cerebrospinal fluid and cortical vasculature (PCC) for predicting brain strain and brain/skull displacement. Second, rapid head rotations resulting in various degrees of IH were simulated (n = 24) to determine the biomechanical predictor and injury threshold most closely correlated with IH. FE models representing the PCC with either spring connectors or solid elements between the brain and skull resulted in peak brain strain and brain/skull displacement similar to measured values in situ. However, when predicting IH, the spring connector representation of the PCC had the best predictive capability for IH with a sensitivity of 80% and a specificity of 85% when ≥1% of all spring connectors had at least a peak strain of 0.31 mm/mm. These findings and reported methodology will be used in the development of a human infant FE model to simulate real-world falls and identify injury thresholds for predicting IH in infants

Anthropomorphic Simulations of Falls, Shakes, and Inflicted Impacts in Infants

Object: Rotational loading conditions have been shown to produce subdural hemorrhage and diffuse axonal injury. No experimental data are available with which to compare the rotational response of the head of an infant during accidental and inflicted head injuries. The authors sought to compare rotational deceleration sustained by the head among free falls, from different heights onto different surfaces, with those sustained during shaking and inflicted impact. Methods: An anthropomorphic surrogate of a 1.5-month-old human infant was constructed and used to simulate falls from 0.3 m (1 ft), 0.9 m (3 ft), and 1.5 m (5 ft), as well as vigorous shaking and inflicted head impact. During falls, the surrogate experienced occipital contact against a concrete surface, carpet pad, or foam mattress. For shakes, investigators repeatedly shook the surrogate in an anteroposterior plane; inflicted impact was defined as the terminal portion of a vigorous shake, in which the surrogate’s occiput made contact with a rigid or padded surface. Rotational velocity was recorded directly and the maximum (peak–peak) change in angular velocity ( max) and the peak angular acceleration ( max) were calculated. Analysis of variance revealed significant increases in the max and max associated with falls onto harder surfaces and from higher heights. During inflicted impacts against rigid surfaces, the max and max were significantly greater than those measured under all other conditions. Conclusions: Vigorous shakes of this infant model produced rotational responses similar to those resulting from minor falls, but inflicted impacts produced responses that were significantly higher than even a 1.5-m fall onto concrete. Because larger accelerations are associated with an increasing likelihood of injury, the findings indicate that inflicted impacts against hard surfaces are more likely to be associated with inertial brain injuries than falls from a height less than 1.5 m or from shaking

Longitudinal Evaluation of Eye Misalignment and Eye Movements Following Surgical Correction of Strabismus in Monkeys

Purpose: Strabismus correction surgery is well documented in both the literature and practice with varying levels of success and permanence. Our goal was to characterize longitudinal changes in eye alignment and eye movements following strabismus correction surgery in a monkey model for developmental strabismus. Methods: We studied two juvenile rhesus monkeys with exotropia previously induced via an optical prism-rearing paradigm in infancy. Eye misalignment was corrected via a resection–recession surgery of the horizontal rectus muscles of one eye. Binocular search coils were used to collect eye movement data during smooth-pursuit, saccades, and fixation tasks before surgical treatment, immediately after surgery, and through 6 months after treatment. Results: Both animals showed an immediate ?70% reduction in misalignment as a consequence of surgery that regressed to a 20%–40% improvement by 6 months after treatment. Significant changes were observed in saccade and smooth-pursuit gain of the nonviewing eye after surgery, which also reverted to presurgical values by 6 months. A temporary improvement in fixation stability of the nonviewing eye was observed after surgery; naso-temporal (N/T) asymmetry of monocular smooth-pursuit remained unchanged. Conclusions: Surgical realignment is followed by plastic changes that often lead to reversal of surgery effects. Immediate improvement in misalignment and changes in eye movement gains are likely a result of contractility changes at the level of the extraocular muscle, whereas longer-term effects are likely a combination of neural and muscle adaptation

Changes in Vitreoretinal Adhesion With Age and Region in Human and Sheep Eyes

While several studies have qualitatively investigated age- and region-dependent adhesion between the vitreous and retina, no studies have directly measured the vitreoretinal strength of adhesion. In this study, we developed a rotational peel device and associated methodology to measure the maximum and steady-state peel forces between the vitreous and the retina. Vitreoretinal adhesion in the equator and posterior pole were measured in human eyes from donors ranging 30 to 79 years of age, and in sheep eyes from premature, neonatal, young lamb, and young adult sheep. In human eyes, maximum peel force in the equator (7.24 ± 4.13 mN) was greater than in the posterior pole (4.08 ± 2.03 mN). This trend was especially evident for younger eyes from donors 30 to 39 years of age. After 60 years of age, there was a significant decrease in the maximum equatorial (4.69 ± 2.52 mN, p = 0.016) and posterior pole adhesion (2.95 ± 1.25 mN, p = 0.037). In immature sheep eyes, maximum adhesion was 7.60 ± 3.06 mN, and did not significantly differ between the equator and posterior pole until young adulthood. At this age, the maximum adhesion in the equator nearly doubled (16.67 ± 7.45 mN) that of the posterior pole, similar to the young adult human eyes. Light microscopy images suggest more disruption of the inner limiting membrane (ILM) in immature sheep eyes compared to adult sheep eyes. Interestingly, in human eyes, ILM disruption was significantly greater in the posterior pole (p < 0.05) and in people over 60 years of age (p < 0.02). These findings supplement the current discussion surrounding age-related posterior vitreous detachment, and the risk factors and physiological progressions associated with this condition. In addition, these data further our understanding of the biomechanical mechanisms of vitreoretinal adhesion, and can be used to develop age- appropriate computational models simulating retinal detachment, hemorrhaging, or retinal trauma

Mechanics of head impact in infants

Falls are the most common unintentional injury modality among infants, as well as the most common history provided by caretakers in cases of suspected child abuse. Skull fracture is a common finding for both violence-related and unintentional head injuries, and it is not clear what fall heights cause skull fracture in young children. Material property testing of human infant skull and suture, anthropomorphic surrogate simulations, and finite element modeling were combined to determine the fall heights capable of creating skull fracture. The ultimate stress of human adult cranial bone at high test rates is more than 5 times higher than pediatric cranial bone, indicating a lower threshold for fracture. However, adult cranial bone was found to be 48 times stiffer than pediatric cranial bone, and pediatric cranial suture was able deform over 100% before failure, producing an infant skullcase that may significantly deform before fracture, increasing the potential for brain deformation and injury upon impact. Angular accelerations calculated from surrogate simulations of head-first falls from 1-3 feet reveal that drops onto mattress produce significantly lower rotational accelerations than carpet and concrete. Drops onto carpet pad were not significantly different than concrete due to compression of the carpet pad and underlying concrete surface. Sagittal and axial rotation accounted for the majority of head motion during all drops. Using measured material property data and loads from the surrogate simulations, a 3D finite element model of a 1-½ month old infant head predicted that a 280 N impact force onto the occiput would result in a 50% probability of skull fracture in infants. Based on the range of forces calculated for the fall simulations of average head-first impacts, we conclude that there is ≥ 50% probability of skull fracture in infants with head-first impact to the occiput from falls of 1-3 feet onto carpet pad and concrete, but not onto a mattress. By defining biomechanical tolerances of pediatric tissues and mechanisms of injury, better accident prevention methods may be developed, and clinicians will be better equipped to make objective assessments of injury etiologies in infants

Longitudinal Evaluation of Eye Misalignment and Eye Movements Following Surgical Correction of Strabismus in Monkeys

PURPOSE. Strabismus correction surgery is well documented in both the literature and practice with varying levels of success and permanence. Our goal was to characterize longitudinal changes in eye alignment and eye movements following strabismus correction surgery in a monkey model for developmental strabismus. METHODS. We studied two juvenile rhesus monkeys with exotropia previously induced via an optical prism-rearing paradigm in infancy. Eye misalignment was corrected via a resectionrecession surgery of the horizontal rectus muscles of one eye. Binocular search coils were used to collect eye movement data during smooth-pursuit, saccades, and fixation tasks before surgical treatment, immediately after surgery, and through 6 months after treatment. RESULTS. Both animals showed an immediate~70% reduction in misalignment as a consequence of surgery that regressed to a 20%-40% improvement by 6 months after treatment. Significant changes were observed in saccade and smooth-pursuit gain of the nonviewing eye after surgery, which also reverted to presurgical values by 6 months. A temporary improvement in fixation stability of the nonviewing eye was observed after surgery; naso-temporal (N/T) asymmetry of monocular smooth-pursuit remained unchanged. CONCLUSIONS. Surgical realignment is followed by plastic changes that often lead to reversal of surgery effects. Immediate improvement in misalignment and changes in eye movement gains are likely a result of contractility changes at the level of the extraocular muscle, whereas longer-term effects are likely a combination of neural and muscle adaptation