The biomechanics of injury and prevention

<div class="htmlview paragraph">Twelve side impact sled tests were performed using a horizontally accelerated sled and a Heidelberg-type seat fixture. The purpose of these tests was to better understand biomechanical response and injury tolerance in whole-body side impacts. In these tests the subject's whole body impacted a sidewall with one of three surface conditions: 1) a flat, rigid side wall, 2) a side wall with a 6″ pelvic offset, or 3) a flat, padded side wall. This paper presents the biomechanical response and injury tolerance data obtained for the pelvis. Peak values of sacral-y acceleration, pelvic force, compression and velocity x compression were evaluated as predictors of pelvic injury. Based on Logist analysis, Vmax x Cmax was the best predictor of probability of pelvic fracture in this test series, while peak pelvic force and peak compression also performed well.</div>

This article is the first of two parts of a comprehensive survey of the biomechanics of head injury since its inception in 1939 in the United States, the separation being made for temporal and spatial reasons. The second portion of this material will be published at a later time in this journal. The discussion will be almost exclusively limited to nonpenetrating events. The topics presented in the following sections include an introduction that discusses the magnitude of the problem, the basic tools of biomechanics, and significant major reference sources covering this subject. This is succeeded by a brief description of the components of the head, classification of head injuries, early experimental investigations and human tolerance considerations, measurement techniques of kinetic parameters, and head motion and head injury investigations prior to 1966. A Head Injury Conference sponsored by the National Institutes of Neurological Diseases and Stroke in 1966 changed the landscape of investigations in this area. While informal collaboration between neurosurgeons and engineers had existed prior to this time, the conference established a permanent mechanism of synergism between these disciplines, produced the first zero-order realistic model of biomechanical head injury investigation, and established a 4-year program of federally funded research into the mechanical properties of the tissues of the cranium. While a recession precluded a continuation of the national sponsorship of such work, this 4-year period of intensive research resulted in a nationwide individual effort to develop further knowledge in this area. The current presentation, then, covers the mechanical and structural properties of solid and fluid tissues of the head, emphasizing progress during the past 3 decades; fetal cranial properties; analytical and numerical head injury models; experimental cranial loads applied to human volunteers and cadaver heads, dynamic loading of surrogate heads; and, finally, head injury mechanisms. The future publication will encompass experimental, analytical, and some numerical and regulatory information and that will be divided into the following sections: 1. head injury experimentation involving translatory and rotational motion: equipment, subjects and mechanical and physiological consequences 2. diffuse axonal injury: production and traumatic effects; mechanical properties at the axonal and neuronal level 3. vehicular crash investigation and simulation: reconstruction methodologies, staging, surrogate validation, and occupant protection, including vehicular design 4. injury thresholds and tolerances, including skull and vessel failure and brain and brainstem damage, including consideration of loading directions 5. criteria for head injury: governmental and industry regulations, including effects of combined motion- and tissue-level loading 6. further discussions of cranial component properties and injury mechanisms 7. sports head injury considerations: boxing, baseball, softball, football, ice hockey, and skiing activities; protective head devices for these activities 8. vehicular protective devices: design, efficacy, standards, and limitations; models for helmets and experimental validation. This presentation is based on my nearly 4 decades of head injury research, continuous collaboration and discussions with prominent members of the neurosurgical and orthopedic community, and an exhaustive, 2-year search of the literature. While every effort has been made to include all relevant information, it is inevitable that some important research has not come to my attention, and I apologize for any such omissions. It is hoped that this survey will serve as a resource for researchers and practitioners in the area of traumatic head injury and provide a roadmap for further investigations that are urgently needed. For example, this could include a determination of the rate of absorption of blood emitted from broken vessels, and, hopefully, some correlation between mechanical failure and physiological dysfunction of the various relevant tissues of the head. Although a good beginning has been initiated, additional information at the neuronal and axonal level concerning the effect of loading on function as well as age-related changes in geometry and tissue properties is also needed.

<div class="htmlview paragraph">Late model passenger cars and light trucks incorporate occupant protection systems with airbags and knee restraints. Knee restraints have been designed principally to meet the unbelted portions of FMVSS 208 that require femur load limits of 10-kN to be met in barrier crashes up to 30 mph, +/- 30 degrees utilizing the 50% male Anthropomorphic Test Device (ATD). In addition, knee restraints provide additional lower-torso restraint for belt-restrained occupants in higher-severity crashes.</div> <div class="htmlview paragraph">An analysis of frontal crashes in the University of Michigan Crash Injury Research and Engineering Network (UM CIREN) database was performed to determine the influence of vehicle, crash and occupant parameters on knee, thigh, and hip injuries. The data sample consists of drivers and right front passengers involved in frontal crashes who sustained significant injuries (Abbreviated Injury Scale [AIS] ≥ 3 or two or more AIS ≥ 2) to any body region.</div> <div class="htmlview paragraph">At the time of the analysis, the database included 138 occupants who were involved in frontal collisions, and eighty-one of these occupants sustained one or more AIS 2+ injuries to the knee, thigh, and/or hip (KTH). Most of these KTH injuries occurred for crash severities that are equal to, or less than, those used for current federal regulation and consumer information crash testing. The percentage of drivers sustaining KTH injuries is higher than for right-front passengers, and most KTH injuries occurred with little or no rearward intrusion of the toepan or lower instrument-panel/knee restraint.</div> <div class="htmlview paragraph">The data show that a higher percentage of belt-restrained occupants with airbags and knee restraints sustained hip injuries than belt-restrained occupants in vehicles without airbags and knee restraints.</div> <div class="htmlview paragraph">Comparison of the percentage of unbelted occupants sustaining hip injuries in vehicles with and without airbag/knee-restraint systems could not be made because the CIREN database does not contain sufficient numbers of unbelted occupants in vehicles without airbags.</div> <div class="htmlview paragraph">Hip injuries occurring in UM CIREN frontal crashes are predominately acetabular fractures. While hip injuries are not directly life threatening, they are generally far more disabling and costly in the long term than thigh and knee injuries. These disabling hip injuries are more frequent among taller male drivers, and are nearly equally distributed among adult occupants of all ages. Although hip injuries occurred more frequently to unbelted occupants, many belt-restrained occupants also sustained hip fractures. Hip injuries tend to occur on the side of the body towards the damaged area of the vehicle front end and/or the principal direction of force.</div> <div class="htmlview paragraph">The results of this study suggest that the current 10-kN limit on femur loads in federal testing may not be sufficient to address hip-injury risk in real-world frontal crashes. They also suggest a need for a better understanding of the biomechanics of hip injuries and injury tolerance from forces generated by knee loading transmitted through the thigh, and a need for improved biofidelity and instrumentation of the ATD knee, thigh, hip complex.</div>

A review of published research is presented to examine human cervical spine injury epidemiology, classification, mechanism, and tolerance. Synthesis of the literature identifies several areas of cervical spine injury biomechanics in which the current understanding is greater than that suggested by individual investigations. Specifically, epidemiologic studies show an age dependent variation in the location of cervical spine injury. A classification scheme is developed on the basis of published work, in which the classes are defined by the resultant force acting at the site of injury. Further, for compression injuries it appears that a compression force tolerance criterion exists, and that eccentricity of the compressive force can be used to predict the type of cervical injury produced. However, to date, prediction of location of injury within the cervical spine has not been attempted. In particular, a compressive tolerance criterion is suggested between 2.75 and 3.44 kN for the adult cervical spine. In contrast, tolerance criteria for cervical injuries in other forms of loading are less well characterized. Review of the literature on spinal cord injury biomechanics and pediatric cervical spine injury reinforces the need for continued investigation in these areas.

s: Brain impact injury is the leading cause of death in traffic accidents. In this paper, a brain multi-functional rotary impacting platform will first be set up. After this, the living animal brain sagittally rotary impacts will be executed and the injury tolerance will be achieved. Then, the sagittal physical models of animal and human brains will be produced and the four-point markers will be placed widely on the models sagittal sections. In succession, the high-speed camera and the three-dimension infrared motion analysis meter will be used to record the rotary impacting process, the exterior angular acceleration course and the shearing strain data of interior four-point markers. Thus, with the exterior angular acceleration course, the living animals experiments and the experiments based on the animal physical brain model can be coupled equivalently. In the same way, through the maximum shearing strain data of interior four-point markers, the experiments based on the animal physical brain model can be equivalently coupled with the experiments based on the human physical brain model. Finally, according to the comparability in pathology and physiology between animal and human brain tissue, the injury tolerance of human brain under its sagittally rotary impacts can expect to be obtained through the mechanics study.

Development and multi-level validation of a computational model to predict traumatic aortic injury.

Impact biomechanics research in occupant safety predominantly focuses on the effects of loads applied to human subjects during automotive collisions. Characterization of the biomechanical response under such loading conditions is an active and important area of investigation. However, critical knowledge gaps remain in our understanding of human biomechanical response and injury tolerance under vertically accelerated loading conditions experienced due to underbody blast (UBB) events. This knowledge gap is reflected in anthropomorphic test devices (ATDs) used to assess occupant safety. Experiments are needed to characterize biomechanical response under UBB relevant loading conditions. Matched pair experiments in which an existing ATD is evaluated in the same conditions as a post mortem human subject (PMHS) may be utilized to evaluate biofidelity and injury prediction capabilities, as well as ATD durability, under vertical loading. To characterize whole body response in the vertical direction, six whole body PMHS tests were completed under two vertical loading conditions. A series of 50th percentile hybrid III ATD tests were completed under the same conditions. Ability of the hybrid III to represent the PMHS response was evaluated using a standard evaluation metric. Tibial accelerations were comparable in both response shape and magnitude, while other sensor locations had large variations in response. Posttest inspection of the hybrid III revealed damage to the pelvis foam and skin, which resulted in large variations in pelvis response. This work provides an initial characterization of the response of the seated hybrid III ATD and PMHS under high rate vertical accelerative loading.

The biomechanical response and injury tolerance of the shoulder in lateral impacts is not well understood. These data are needed to better understand human injury tolerance, validate finite element models and develop biofidelic shoulders in side impact dummies. Seventeen side impact sled tests were performed with unembalmed human cadavers. Data analyzed for this study include T1-Y acceleration, shoulder and thoracic load plate forces, upper sternum x and y accelerations, and struck side acromion x, y and z accelerations. One dimensional deflection at the shoulder level was determined from high-speed film by measuring the distance between a target on T1 and the impacted wall. Force-time response corridors were obtained for tests with 9 m/s pelvic offset, 10.5 m/s pelvic offset, 9 m/s unpadded flat wall, 6.7 m/s unpadded flat wall, 9 m/s soft padding and 9 m/s stiff padding. Maximum shoulder plate forces in unpadded 9 m/s tests (5.5 kN) were larger than in 6.7 m/s tests (3.3 kN). The peak force at the shoulder was larger than at the thorax plate in unpadded and soft padded tests. T1-Y accelerations were larger in unpadded 9 m/s flat wall tests and unpadded pelvic offset 10.5 m/s tests (peak values of 130 and 145 g's) than in other test conditions. Deflections between T1 and the struck wall ranged from 88 to 154 mm in unpadded tests and 95 to 128 mm in stiff and soft padded tests. Eighteen AIS 2 level shoulder injuries occurred in 11 test subjects. These injuries included left acromion fracture in five subjects, left acromioclavicular separation in ten subjects and left clavicle fracture in three subjects. Average MAIS to the shoulder was 0.86 in seven subjects which impacted 4 to 6 inches (101.6 to 152.4 mm) of soft or stiff padding and 1.6 in ten subjects which impacted no padding or 3 inches (76.2 mm) of stiff padding. Previous findings from this test series were reported by Irwin et al. (1993) for seven tests and focused on detailed analysis of shoulder deflection (T5 to shoulder edge). The current study is expanded to 17 tests and includes force, acceleration response and analysis of shoulder deflection (T1 to shoulder edge). Padding of 4 to 6 inches (101.6 mm to 152.4 mm) reduced shoulder injury approximately one AIS level. A combination of ASA10 and deflection was the best shoulder injury predictor. Shoulder deflection of 106 mm predicts 50% probability of MAIS 2.

The lower limbs play an important role in daily human activities. Therefore, a 3D tibial model is constructed, and finite element analysis is performed to investigate the biomechanical characteristics and injury tolerance of lower limb flexion movement. The maximum equivalent stress at 30° flexion was 19.1 MPa and 31.2 MPa in the normal and dynamic eversion positions, respectively, of the knee joint, 1.4 MPa and 1.1 MPa in the medial tibial plateau, and 1.8 MPa and 1.2 MPa in the lateral tibial plateau. The peak contact force was generally approximately 4000 N when different positions of the tibia were impacted. The maximum contact force of the frontal impact was larger than that of the external impact at 4109 N and 3927 N, respectively. The dynamic knee valgus posture and lateral impacts are more likely to cause tibial injury. The findings of this study provide information for the prevention of sports injuries and rehabilitation treatment.

Statistical shape analysis of clavicular cortical bone with applications to the development of mean and boundary shape models

To date, several lateral impact studies (Bolte et al., 2000, 2003, Marth, 2002 and Compigne et al., 2004) have been performed on the shoulder to determine the response characteristics and injury threshold of the shoulder complex. Our understanding of the biomechanical response and injury tolerance of the shoulder would be improved if the results of these tests were combined. From a larger data base shoulder injury tolerance criteria can be developed as well as corridors for side impact dummies. Data from the study by Marth (2002, 12 tests) was combined with data from the previous studies. Twenty-two low speed tests (4.5 +/- 0.7 m/s) and 9 high speed tests (6.7 +/- 0.7 m/s) were selected from the combined data for developing corridors. Shoulder force, deflection and T1y acceleration corridors were developed using a minimization of cumulative variance technique. The reduction in impact speed and the addition of padding reduced the magnitude and increased the time to peak of shoulder forces and T1y accelerations. Logistic analyses were performed on the combined data sets to determine the best predictors of MAIS-2 shoulder injuries. Maximum normalized shoulder deflection and Cmax had p values of 0.0000 and were the best predictors of shoulder injuries. For the 50(th)-percentile male, a shoulder deflection of 40 mm and a Cmax of 20% corresponded to a 50 % risk of MAIS-2 shoulder injury. In linear regression analysis, maximum normalized medial scapula X acceleration and maximum normalized sternum X acceleration were best related with the shoulder deflection and confirmed the forward movement of the sternum and rearward movement of the scapula.

This chapter summarizes research on the injury mechanisms, tolerances, and responses of the whole knee-thigh-hip (KTH) complex and its components to dynamic loading. The focus is on KTH injury to seated adult vehicle occupants and pedestrians involved in road traffic crashes. Injuries from falls, sports, and other activities are not specifically discussed, although much of the injury biomechanical research described is relevant to these activities.

This article summarizes content proceedings of a satellite meeting held at the 2004 Research Society on Alcoholism Annual Scientific Meeting in Vancouver, Canada. The aim of the satellite conference was to facilitate the interaction of scientists investigating the mechanisms of alcohol-mediated organ or tissue damage, and enable the discussion and sharing of new ideas and concepts that may be common in each of the organs or tissues affected by chronic ethanol consumption. The original planned program on immunity was expanded to incorporate a session on a closely related topic "Alcohol and Mitochondrial Metabolism: At the Crossroads of Life and Death" organized by Dr. Jan Hoek and Dr. Sam Zakhari. The conference was arranged into four sessions: 1) Alcohol, Cellular and Organ Damage 2) Toll-like receptors and Organ Damage 3) Alcohol and Mitochondrial Metabolism: At the Crossroads of Life and Death and 4) Hepatitis virus and alcohol interactions in Immunity and Liver Disease. The keynote address was given by Dr. Bruce Beutler from the Scripps Institute on "TLRs in Inflammation and Immunity."The Combined Basic Research Satellite Symposium entitled, "Mechanisms of Alcohol-Mediated Organ and Tissue Damage: Inflammation and Immunity and Alcohol and Mitochondrial Metabolism: At the Crossroads of Life and Death" was convened at the 2004 Research Society on Alcoholism meeting in Vancouver, BC. Session One featured five speakers who discussed various aspects of the role of the immune system in initiating or exacerbating cellular and organ damage following alcohol consumption. The presentations were (1) Innate Immune responses of Alcohol-exposed mice and macrophage-like cells following infections with Listeria monocytogenes by Robert T. Cook 2) Alcohol, cytokines and host defense by Kyle Happel 3) Decreased antigen presentation and anergy induced by alcohol in myeloid dendritic cells by Pranoti Mandrekar 4) Transcriptional regulation of TNF-alpha in human monocytes by chronic ethanol: role of the cellular redox state by Jay Kolls 5) Estrogen and gender differences in inflammatory responses after alcohol and burn injury by Elizabeth Kovacs. This session highlighted the growing information on the role of pattern recognition molecules in alcohol-mediated tissue damage or dysfunction. The new techniques and ideas presented will be helpful in future studies in this area of research, and should result in some exciting avenues of study.

From 1990 to approximately 50,000–120,000 people die annually of road traffic accidents in China. Traffic accidents are the main cause of death of Chinese adults aged 15–45 years. This study aimed to determine the biomechanical response and injury tolerance of the human body in traffic accidents. The subject was a 35-year-old male with a height of 170 cm, weight of 70 kg and Chinese characteristics at the 50th percentile. Geometry was generated by computed tomography and magnetic resonance imaging. A human-body biomechanical model was then developed. The model featured in great detail the main anatomical characteristics of skeletal tissues, soft tissues and internal organs, including the head, neck, shoulder, thoracic cage, abdomen, spine, pelvis, pleurae and lungs, heart, aorta, arms, legs, and other muscle tissues and skeletons. The material properties of all tissues in the human body model were obtained from the literature. Material properties were developed in the LS-DYNA code to simulate the mechanical behaviour of the biological tissues in the human body. The model was validated against cadaver responses to frontal and side impact. The predicted model response reasonably agreed with the experimental data, and the model can further be used to evaluate thoracic injury in real-world crashes. We believe that the transportation industry can use numerical models in the future to simultaneously reduce physical testing and improve automotive safety.

Editorial: When Physics Meets Biology; Biomechanics and Biology of Traumatic Brain Injury.