Francisco J. López-Valdés

Pedestrian injuries in eight European countries: An analysis of hospital discharge data

Out of the 50,000 yearly road traffic deaths in the European Union (formed by 27 European countries and commonly designated as EU-27), some 8500 are pedestrians. While some studies focus on the increased risk for pedestrian mortality compared to other road users, there is a dearth of information on injury patterns that could be used to prioritize injury prevention measures. Hospital discharge data from eight European countries have been used in this study. Injury information from 10,341 pedestrians sustaining 19,424 injuries has been analyzed. Data have been augmented with Abbreviated Injury Scale, Functional Capacity Index and Injury Severity Score codes, and have been categorized into the Barell Matrix. Fractures (51.1%, 50.3-51.8) and internal injuries (21.3%, 20.7-21.9) are the most frequently found in the data; however, blood vessel injuries and internal injuries are the ones associated with the highest risk of death. Head and lower extremities account for 26% of the injuries each, being spinal and thoracic injuries those showing the highest threat to life risk. Hip and lower extremities injuries are the most frequent cause of functional limitation 1 year after discharge. Due to its intrinsic importance, different injury causation mechanisms for head injuries have been analyzed. Though current standards and regulations consider Head Injury Criterion (HIC) as the only tool to assess the risk of injuries to the head, real world injury data show that only 12.1% (11.0-13.2) of these injuries can be attributed to a pure translational mechanism and therefore susceptible to be predicted by HIC. Design of prevention strategies, particularly from the engineering point of view, should benefit from this information.

Injuries among powered two-wheeler users in eight European countries: A descriptive analysis of hospital discharge data

Powered two-wheelers (PTWs--mopeds, motorcycles, and scooters) remain the most dangerous form of travel on todays roads. This study used hospital discharge data from eight European countries to examine the frequencies and patterns of injury among PTW users (age≥14 years), the predicted incidence of the loss of functional ability, and the mechanisms of the head injuries observed (all in light of increased helmet use). Of 977,557 injured patients discharged in 2004, 12,994 were identified as having been injured in PTW collisions. Lower extremity injuries accounted for 26% (25.6-26.7, 95% C.I.) of the total injuries, followed by upper extremity injuries (20.7%: 20.3-21.2), traumatic brain injuries (TBI) (18.5%: 18-19), and thoracic injuries (8.2%: 7.8-8.5). Approximately 80% of the lower extremity injury cases were expected to exhibit some functional disability one year following discharge (predicted Functional Capacity Index, pFCI-AIS98<100), compared to 47% of the upper extremity injury cases and 24% of the TBI cases. Although it occurred less frequently, patients that were expected to experience some functional limitation from TBI were predicted to fair worse on average (lose more functional ability) than patients expected to have functional limitations from extremity injuries. Cerebral concussion was the most common head injury observed (occurring in 56% of head injury cases), with most concussion cases (78%) exhibiting no other head injury. Among the AIS3+ head injuries that could be mapped to an injury mechanism, 48% of these were associated with a translational-impact mechanism, and 37% were associated with a rotational mechanism. The observation of high rates of expected long-term disability suggests that future efforts aim to mitigate lower and upper extremity injuries among PTW users. Likewise, the high rates of concussion and head injuries associated with a rotational mechanism provide goals for the next phase of PTW user head protection.

Kinetics of the cervical spine in pediatric and adult volunteers during low speed frontal impacts

Previous research has quantified differences in head and spinal kinematics between children and adults restrained in an automotive-like configuration subjected to low speed dynamic loading. The forces and moments that the cervical spine imposes on the head contribute directly to these age-based kinematic variations. To provide further explanation of the kinematic results, this study compared the upper neck kinetics - including the relative contribution of shear and tension as well as flexion moment - between children (n=20, 6-14 yr) and adults (n=10, 18-30 yr) during low-speed (<4 g, 2.5 m/s) frontal sled tests. The subjects were restrained by a lap and shoulder belt and photo-reflective targets were attached to skeletal landmarks on the head, spine, shoulders, sternum, and legs. A 3D infrared tracking system quantified the position of the targets. Shear force (F(x)), axial force (F(z)), bending moment (M(y)), and head angular acceleration (θ(head)) were computed using inverse dynamics. The method was validated against ATD measured loads. Peak F(z) and θ(head) significantly decreased with increasing age while M(y) significantly increased with increasing age. F(x) significantly increased with age when age was considered as a univariate variable; however when variations in head-to-neck girth ratio and change in velocity were accounted for, this difference as a function of age was not significant. These results provide insight into the relationship between age-based differences in head kinematics and the kinetics of the cervical spine. Such information is valuable for pediatric cervical spine models and when scaling adult-based upper cervical spine tolerance and injury metrics to children.

A Parametric Study of Hard Tissue Injury Prediction Using Finite Elements: Consideration of Geometric Complexity, Subfailure Material Properties, CT-Thresholding, and Element Characteristics

Objective: The objectives of this study were to examine the axial response of the clavicle under quasistatic compressions replicating the body boundary conditions and to quantify the sensitivity of finite element–predicted fracture in the clavicle to several parameters. Methods: Clavicles were harvested from 14 donors (age range 14–56 years). Quasistatic axial compression tests were performed using a custom rig designed to replicate in situ boundary conditions. Prior to testing, high-resolution computed tomography (CT) scans were taken of each clavicle. From those images, finite element models were constructed. Factors varied parametrically included the density used to threshold cortical bone in the CT scans, the presence of trabecular bone, the mesh density, Youngs modulus, the maximum stress, and the element type (shell vs. solid, triangular vs. quadrilateral surface elements). Results: The experiments revealed significant variability in the peak force (2.41 ± 0.72 kN) and displacement to peak force (4.9 ± 1.1 mm), with age (p < .05) and with some geometrical traits of the specimens. In the finite element models, the failure force and location were moderately dependent upon the Youngs modulus. The fracture force was highly sensitive to the yield stress (80–110 MPa). Conclusion: Neither fracture location nor force was strongly dependent on mesh density as long as the element size was less than 5 × 5 mm2. Both the fracture location and force were strongly dependent upon the threshold density used to define the thickness of the cortical shell.

Injury Severity Scaling

Injury prevention research often entails describing the severity of injuries or controlling for the severity of injuries when comparing outcomes. Basically, injury severity scores are required to either prioritize interventions at the patient level (e.g., triage, medical care) or population level as well as when evaluating the effectiveness of injury control and prevention interventions. A number of injury severity scales have emerged since the 1960s and share specific characteristics, although they are conceptually different. The goal of this chapter is to describe the most commonly used injury severity scales in injury research and control. A number of dimensions associated with both the development and the usage of the injury scales are proposed to ease the comparison of the scales as well as to improve the understanding of the underlying concepts involved in their origin. Methodological issues related to their use in research environments are also highlighted. To conclude, this chapter discusses some of the existing challenges in injury severity measurement such as the need for further refinement of the concept itself, further methodological work on the scales themselves, and resolution of the debate on whether consensus-based or real-world severity scales are better.

The Frontal-Impact Response of a Booster-Seated Child-Size PMHS

Objectives: This article presents the response of a child-size postmortem human subject using a booster seat in a series of three frontal impact sled tests. Methods: A 54-year-old female cadaver was seated in a booster seat in the rear seat of a buck representing a mid-sized American sedan. Two different restraint systems (conventional belt and pretensioning, force-limiting belt) were used to run three simulated frontal impacts (one at 29 km/h, two at 48 km/h). Instrumentation included accelerometers rigidly mounted on relevant body landmarks as well as chest bands. Trajectories were assessed through high-speed video cameras. Results: Specific focus was on the whole-body kinematics and resulting head trajectories under two different restraint conditions (booster seat and standard belt, booster seat and force-limiting pretensioning belt) in a rear seat environment. At 48 km/h, the pretensioning, force-limiting seat belt reduced the forward excursion of both the head (353 mm vs. 424 mm) and the h-point (120 mm vs. 152 mm) compared to the standard system. Maximum torso pitch was similar for both seat belts. Conclusions: A complete description of the outcome of the tests is presented in the article. These results suggest that the introduction of a pretensioning force limiting belt in the rear seat can be beneficial for small size occupants like children using booster seats.

A Comparison of the Performance of Two Advanced Restraint Systems in Frontal Impacts

Objective: The goal of the study is to compare the kinematics and dynamics of the THOR dummy in a frontal impact under the action of 2 state-of-the-art restraint systems. Methods: Ten frontal sled tests were performed with THOR at 2 different impact speeds (35 and 9 km/h). Two advanced restraint systems were used: a pretensioned force-limiting belt (PT+FL) and a pretensioned belt incorporating an inflatable portion (PT+BB). Dummy measurements included upper and lower neck reactions, multipoint thoracic deflection, and rib deformation. Data were acquired at 10,000 Hz. Three-dimensional motion of relevant dummy landmarks was tracked at 1,000 Hz. Results are reported in a local coordinate system moving with the test buck. Results: Average forward displacement of the head was greater when the PT+FL belt was used (35 km/h: 376.3 ± 16.1 mm [PT+BB] vs. 393.6 ± 26.1 mm [PT+FL]; 9 km/h: 82.1 ± 26.0 mm [PT+BB] vs. 98.8 ± 0.2 mm [PT+FL]). The forward displacement of T1 was greater for the PT+FL belt at 35 km/h but smaller at 9 km/h. The forward motion of the pelvis was greater when the PT+BB was used, exhibiting a difference of 82 mm in the 9 km/h tests and 95.5 mm in the 35 km/h test. At 35 km/h, upper shoulder belt forces were similar (PT+FL: 4,756.8 ± 116.6 N; PT+BB: 4,957.7 ± 116.4 N). At 9 km/h, the PT+BB belt force was significantly greater than the PT+FL one. Lower neck flexion moments were higher for the PT+BB at 35 km/h but lower at 9 km/h (PT+FL: 34.2 ± 3.5 Nm; PT+BB: 26.8 ± 2.1 Nm). Maximum chest deflection occurred at the chest upper left region for both belts and regardless of the speed. Conclusion: The comparison of the performance of different restraints requires assessing occupant kinematics and dynamics from a global point of view. Even if the force acting on the chest is similar, kinematics can be substantially different. The 2 advanced belts compared here showed that while the PT+BB significantly reduced peak and resultant chest deflection, the resulting kinematics indicated an increased forward motion of the pelvis and a reduced rotation of the occupants torso. Further research is needed to understand how these effects can influence the protection of real occupants in more realistic vehicle environments.

Biomechanical response targets for physical and computational models of the pediatric trunk.

Objectives: This paper quantifies pediatric thoracoabdominal response to belt loading to guide the scaling of existing adult response data and to assess the validity of a juvenile porcine abdominal model for application to the development of physical and computational models of the human child. Methods: Table-top belt-loading experiments were performed on 6, 7, and 15 year-old pediatric post-mortem human subjects (PMHS). Response targets are reported for diagonal belt and distributed loading of the anterior thorax and for horizontal belt loading of the abdomen. Results: The pediatric PMHS exhibited abdominal response similar to the swine, including the degree of rate sensitivity. The thoraces of the PMHS were as stiff as, or slightly more stiff than, published adult corridors. Conclusions: An assessment of age-related changes in thoracic stiffness suggests that the effective stiffness of the chest increases through the fourth decade of life and then decreases, resulting in stiffness values similar for children and elderly adults.

Reduction in the exposure to being out-of-position among car occupants who used a sleeping device

Background This study assesses the impact on safety of a system designed to enhance sleep in car passengers. The system holds the head posteriorly and limits its rotation in the sagittal and frontal planes, modifying the occupants head position. This device may have an influence on the interaction between the occupant and the vehicle restraint systems. Methods It was a randomised, prospective, single-blind, cross-over controlled study in which 41 volunteers were exposed to using the system while riding as car passengers. Whether the device influenced the posture of the occupants and prevented them from adopting out-of-position (OOP) configurations was also analysed. Occupants were videotaped while they were using both the innovative system (cases) and their normal sleeping device (controls), if any. Results Controls were exposed to OOP situations in 825 occasions (18.4%; 95% CI 17.3% to 19.6%), while cases were exposed in 416 occasions (9.3%; 95% CI 8.4% to 10.2%). The paper also analysed how many cases and controls were exposed at least once to a particular event and how frequent a single participant incurred in an OOP situation. In both cases, the innovative device showed a reduction in exposition. When OOP situations were grouped into severe, moderate and minor events, the innovative device produced a statistically significant reduction in the occurrence of severe and moderate events. Conclusions A device originally designed to improve comfort and rest in car passengers has been found to reduce the exposure of the occupants to being OOP while resting in the car. Trial registration number http://www.ClinicalTrials.gov, NCT01062295.

Exposure to Traffic and Risk of Hospitalization Due to Injuries

Research on the risk of motor vehicle injuries and their relationship with the amount of travel has been only partially analyzed. The few individual exposure assessments are related to very specific subsets of the driving and traveling populations. This study analyzes the relationship between kilometers traveled and hospitalization due to motor vehicle injuries. Twelve thousand three hundred and sixty nine Spanish university graduates from the Seguimiento Universidad de Navarra multipurpose cohort study were evaluated. They had not been hospitalized due to motor vehicle injuries at baseline and were followed up to eight years. Biannual questionnaires allowed for self-reporting of kilometers traveled in motor vehicles, together with incidence of hospitalization. Covariates in the Cox regression models included age and gender and baseline use of safety belt while driving, driving a vehicle with driver-side airbag, driving a motorcycle, and drinking and driving. There were 49,766 participant-years with an average yearly travel of 7,828 km per person-year. Thirty-six subjects reported a first hospitalization event during this time. The adjusted hazard ratio per additional kilometer traveled was 1.00005 (95% confidence interval 1.000013 to 1.000086). Even the smallest of reductions in the amount of kilometers traveled (from an average of 3,250 km per year to 1,000) has a statistically significant protective effect on the likelihood of sustaining hospitalization due to motor vehicle injury (aHR 0.9, 95% CI 0.78 to 0.98). In light of current policies aimed to reduce motorized traffic due to environmental concerns, it may be appropriate to consider the additional health benefit related to reductions in injuries.