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Complaints of spinal pain are common after motor vehicle collisions (MVCs), and evaluators may be asked whether the collision caused permanent injury to the spine, including aggravating intervertebral disc degeneration (IDD) and/or causing a disc herniation. To determine causality, evaluators can use the AMA Guides to the Evaluation of Permanent Impairment (AMA Guides) to understand if a low-speed collision caused IDD. Injury causation analysis (ICA) is the scientific method used to analyze the mechanism and magnitude of injury for people who experience an MVC. ICA involves comparing the mechanical forces involved in the incident with the body's injury tolerance. Low back pain (LBP) is a common complaint following MVCs, but the literature regarding automobile collision testing has been compared to the body of evidence regarding real-world collision data and shows that, for low-speed impacts, any injuries are minor and self-limiting. Further, disability due to LBP was predicted by an abnormal baseline psychological test profile or a previously disputed compensation claim. The motions, forces, and accelerations generated in low-speed collisions are less than those encountered in activities of everyday living. ICA suggests that disc degeneration and disc herniations are pre-existing and are not caused by low-speed MVCs. Although the pain caused by a muscle sprain associated with a low-speed collision may prompt imaging studies that show disc pathology, these are coincidental and are not causally related.

Study design This study combined all prior research involving human volunteers in low-speed rear-end impacts and performed a comparative analysis of real-world crashes using the National Automotive Sampling System - Crashworthiness Data System. Objective The aim of this study was to assess the rates of neck pain between volunteer and real-world collisions as well as the likelihood of an injury beyond symptoms as a function of impact severity and occupant characteristics in real-world collisions. Summary of background data A total of 51 human volunteer studies were identified that produced a dataset of 1984 volunteer impacts along with a separate dataset of 515,601 weighted occupants in real-world rear impacts. Methods Operating-characteristic curves were created to assess the utility of the volunteer dataset in making predictions regarding the overall population. Change in speed or delta-V was used to model the likelihood of reporting symptoms in both real-world and volunteer exposures and more severe injuries using real-world data. Logistic regression models were created for the volunteer data and survey techniques were used to analyze the weighted sampling scheme with the National Automotive Sampling System database. Results Symptom reporting rates were not different between males and females and were nearly identical between laboratory and real-world exposures. The minimal risk of injury predicted by real-world exposure is consistent with the statistical power of the large number of volunteer studies without any injury beyond the reporting of neck pain. Conclusion This study shows that volunteer studies do not under-report symptoms and are sufficient in number to conclude that the risk of injury beyond neck strain under similar conditions is essentially zero. The real-world injury analyses demonstrate that rear impacts do not produce meaningful risks of cervical injury at impacts of similar and greater severity to those of the volunteer research. Future work concerning the mechanism of whiplash-related trauma should focus on impacts of severity greater than those in the current literature. Level of evidence 3.

The purpose of this study was to document head and neck loading in a group of ordinary people engaged in non-injurious everyday and more vigorous physical activities. Twenty (20) volunteers that were representative of the general population were subjected to seven test scenarios: a soccer ball impact to the forehead, a self-imposed hand strike to the forehead, vigorous head shaking, plopping down in a chair, jumping off a step, a seated drop onto the buttocks, and a vertical drop while seated supine in a chair. Some scenarios involved prescribed and well-controlled stimuli, while others allowed the volunteers to perform common activities at a self-selected level of intensity. Head accelerations up to 31 g and 2888 rad/s(2) and neck loads up to 268 N in posterior shear, 526 N in compression, and 36 Nm in extension were recorded. Most head and neck injury criteria predicted a low risk of injury in all activities. However, rotational head accelerations and Neck Injury Criterion (NIC) values were much higher than some proposed tolerance limits in a large number of tests, all of which were non-injurious. The data from this study help us to establish an envelope of head and neck loading that is commonly encountered and presents a minimal risk of injury.

The purpose of this study was to develop a numerical analytical model of collinear low-speed bumper-to-bumper crashes and use the model to perform parametric studies of low-speed crashes and to estimate the severity of low-speed crashes that have already occurred. The model treats the car body as a rigid structure and the bumper as a deformable structure attached to the vehicle. The theory used in the model is based on Newton's Laws. The model uses an Impact Force-Deformation (IF-D) function to determine the impact force for a given amount of crush. The IF-D function used in the simulation of a crash that has already occurred can be theoretical or based on the measured force-deflection characteristics of the bumpers of the vehicles that were involved in the actual crash. The restitution of the bumpers is accounted for in a simulated crash through the rebound characteristics of the bumper system in the IF-D function. The output of the model for a numerical simulation is the acceleration vs. time information for each vehicle in the simulated crash. Three low-speed crash tests were performed and the dynamic IF-D curve was measured in each crash. The analytical model was used to simulate the three low-speed crash tests in order to demonstrate the model's ability to describe the vehicle dynamics in a crash that has already occurred. The model is also used to perform parametric studies that show how the structural characteristics of the vehicles' bumpers and the closing speed affect the crash pulse and to demonstrate a technique to estimate the maximum severity of a low-speed crash that has already occurred.

Ejection greatly increases the risk of injury and fatality in a rollover crash. The purpose of this study was to determine the crash, vehicle, and occupant characteristics that affect the risk of ejection in rollovers. Information from real world rollover crashes occurring from 2000 – 2010 was obtained from the National Automotive Sampling System (NASS) in order to analyze the effect of the following parameters on ejection risk: seatbelt use, rollover severity, vehicle type, seating position, roof crush, side curtain airbag deployment, glazing type, and occupant age, gender, and size. Seatbelt use was found to reduce the risk of partial ejection and virtually eliminate the risk of complete ejection. For belted occupants, the risk of partial ejection risk was significantly increased in rollover crashes involving more roof inversions, light trucks and vans (LTVs), and larger occupants. For unbelted occupants, the risk of complete ejection was significantly increased in rollover crashes involving more roof inversions, LTVs, far side occupants, and higher levels of roof crush. Roof crush was not a significant predictor of ejection after normalizing for rollover severity. Curtain airbag deployment was associated with reduced rates of partial and complete ejection, but the effect was not statistically significant, perhaps due to the small sample size (n = 89 raw cases with curtain deployments). A much greater proportion of occupants who were ejected in spite of curtain airbag deployment passed through the sunroof and other portals as opposed to the adjacent side window compared to occupants who were ejected in rollovers without a curtain airbag deployment. The primary factors that reduce ejection risk in rollover crashes are, in generally decreasing order of importance: seatbelt use, fewer roof inversions, passenger car body type, curtain airbag deployment, near side seating position, and small occupant size.

Neck muscle activation is believed to generally protect against whiplash and head injury in automotive impacts and sports activities. When the torso is struck, active tensing of the neck muscles may prevent the neck from rotating excessively due to the inertia of the head. In this scenario, neck muscle tension may also reduce the severity of a secondary head impact occurring after the primary impact with the body. In a direct impact to the head, it has been hypothesized that active neck muscle tension may reduce the acceleration experienced by the head by increasing its effective mass.Copyright © 2011 by ASME

Calculating head accelerations and neck loading is essential for understanding and predicting head and neck injury. Most of the desired information cannot be directly measured in experiments with human volunteers. Achieving accurate results after applying the necessary transformations from remote measurements is difficult, particularly in the case of a head impact. The objective of this study was to develop a methodology for accurately calculating the accelerations at the center of gravity of the head and the loads and moments at the occipital condyles. To validate this methodology in a challenging test condition, twenty (20) human volunteers and a Hybrid III dummy were subjected to forehead impacts from a soccer ball traveling horizontally at speeds up to 11.5 m/s. The human subjects and the Hybrid III were instrumented with linear accelerometers and an angular rate sensor inside the mouth. The dummy was also equipped with accelerometers at the center of gravity of the head and load cells in the upper and lower neck. The force applied to the head by the soccer ball was calculated by double differentiating the ball displacement measured from high speed video. Standard mechanics equations were used to transform mouth accelerations to the head center of gravity and to calculate loads and moments at the occipital condyles. Accurate angular acceleration data were obtained by rigidly mounting a small angular rate sensor inside the mouth on a bite block. The neck loads calculated using inverse dynamics required filtering to a cutoff frequency of 50 Hz in order to reduce the noise to an acceptable level and achieve a good match with the neck load cell data. Noise was a particular problem in the calculated occipital condyle sagittal plane bending moment. Although some differences in the results of the human and dummy tests were observed, The Hybrid III dummy head and neck appeared to be reasonably biofidelic in this loading scenario.

Vehicle dynamics in sideswipe collisions are markedly different from other types of collisions. Sideswipe collisions are characterized by prolonged sliding contact, often with very little structural deformation. An analytical model was developed to investigate the vehicle dynamics of sideswipe collisions. The vehicles were modeled as rigid bodies, and lateral interaction between the vehicles was modeled with a linear elastic spring. This linear spring was meant to represent the combined lateral stiffness of both vehicles before significant crush develops. Longitudinal interaction between the vehicles was modeled as frictional contact. In order to validate the model, seven (7) low speed (3 – 10 kph), shallow angle (15°) sideswipe collisions were staged with instrumented vehicles. These sideswipe collisions were characterized by long contact durations (~ 1 s) and low accelerations (< 0.4 g’s). The experimental collisions were also simulated with EDSMAC. EDSMAC overpredicted peak longitudinal vehicle acceleration by an average of 83% and underpredicted the length of contact damage by an average of 50%. In contrast, the linear spring model accurately predicted the peak longitudinal vehicle acceleration (5% error) when the stiffness parameter was tuned to match the length of contact damage. These results suggest that a noncrush-based linear spring model for calculating intervehicular force could significantly improve the accuracy of reconstructions of low speed sideswipe collisions compared to existing methods such as SMAC.