Janusz Kajzer

CERVICAL INJURY MECHANISM BASED ON THE ANALYSIS OF HUMAN CERVICAL VERTEBRAL MOTION AND HEAD-NECK-TORSO KINEMATICS DURING LOW SPEED REAR IMPACTS

Twelve male volunteers participated in this study. They sat on a seat mounted on a newly developed sled that simulated actual car impact acceleration. Impact speeds (4, 6 and 8 km/h), seat stiffness, neck muscle tension, and cervical spine alignment were selected for the parameter study of the head-neck-torso kinematics and cervical spine responses. The motion patterns of cervical vertebrae in the crash motion and in the normal motion were compared. Subjects muscles in the relaxed state did not affect the head-neck-torso kinematics upon rear-end impact. The ramping-up motion of the subjects torso was observed due to the seatback inclination. An axial compression force occurred when this motion was applied to the cervical spine, which in turn developed the initial flexion, with the lower cervical vertebral segments extended and rotated prior to the motions of the upper segments. Those motions were beyond the normal physiological cervical motion, which should be attributed to the facet joint injury mechanism. The difference in alignment of the cervical spine affected the impact responses of head and neck markedly. Based on the differences in the alignment of the cervical spine between male and female occupants, it is pointed out that the neck injury incidence tends to become higher for women than for men.(A) For the covering abstract of the conference see IRRD E201172.

Comparative analysis of vehicle-bicyclist and vehicle-pedestrian accidents in Japan

Bicyclist and pedestrian injuries in collisions with vehicles in Japan were investigated based on national and in-depth accident data analyses and mathematical simulations. In an impact with a bonnet-type vehicle, a bicyclist slides over the bonnet of the vehicle, behavior that is not observed for pedestrians. As a result, the bicyclists head tends to strike a bonnet-type vehicle at a more rearward location in comparison with pedestrians. The first contact position of a bicycle with a vehicle, the vehicle front-end geometry and the bicycle velocity affect whether the bicyclists head strikes the vehicle or not. Due to the bent-knee posture of a bicyclists legs, the types of leg injuries sustained by bicyclists and their causes differ from those seen for pedestrians. Component test procedures have been proposed for evaluating pedestrian safety, but some modifications of the head impact area and angle are necessary when applying these methods to bicyclists.

Shearing and Bending Effects at the Knee Joint at High Speed Lateral Loading

The main objective of this study is to determine the damage tolerance and describe the damage mechanisms of the extended human knee when it is exposed to lateral impact loads in car-pedestrian accidents, particularly those that occur at a low velocity (20 kph), and compare the results with those obtained at a high velocity (40 kph). In-Vitro experiments with human subjects were conducted where only the purest possible shearing deformation or the purest possible bending deformation affected the knee region. When the knee joint was exposed to deformation, the common initial damage mechanism was ligament damage related to ACL (60%). This type of damage occurred when mean values of the peak shearing force and the peak bending moment acting at the knee joint level were 2.4 kN and 418 Nm, and the shearing displacement and bending angle were 16 mm and -2.9 deg (-0.05 rad), respectively. When the knee joint was exposed to deformation, the most common initial damage mechanism (40%) was ligament damage related to MCL. The mean values of the peak shearing force and the peak bending moment calculated when this damage occurred were 1.6 kN and 358 Nm, respectively. This type of initial damage occurred when the knee was bent 12.3 deg (0.22 rad). The initial metaphysics fracture of the femur due to bending deformation of the knee was observed in only 20% of the cases. The mean values of the peak shearing force and the peak bending moment developed at knee joint level that correspond to this damage were 0.9 kN and 205 Nm. This type of damage occurred when the knee was bent 12.3 deg (0.22 rad). The physical values of the shearing force and the bending moment at the time of initial damage for low-speed lateral loading were found to be similar with those from previously performed experiments at high-speed lateral loading. The ratio of bone fracture to ligament damage was 0.3 in the shearing deformation test and 0.5 in the bending deformation test at low speed.

COMPATIBILITY PROBLEMS IN FRONTAL, SIDE, SINGLE CAR COLLISIONS AND CAR-TO-PEDESTRIAN ACCIDENTS IN JAPAN

Compatibility problems in car-to-car frontal, side, single car and car-to-pedestrian collisions in Japan are discussed using traffic accident data. The number of serious and fatal injuries is investigated for the subject car and other cars, which are categorized by their class and mass. The aggressivity of the cars is calculated by the number of fatalities, fatality rates and by the number of car registrations. The results show that in car-to-car frontal collisions, cars with a mass of 1150 kg are the most compatible among the current car population. In both car-to-car frontal and side collisions, the sports utility vehicle and mini car are found to be the most incompatible car types with high and low aggressivity, respectively. On the other hand, the accident data show that the wagon and midsize sedan are the most compatible car types. The compatibility of fixed objects in the road environment with cars and cars with pedestrians is also discussed. In a single car collision with a fixed object, the guardrail is the most compatible object and can reduce the fatality rate on prefecture roads by about 60%. The front geometry of the car has large effect on compatibility with a pedestrian.

Finite Element Analysis of Knee Injury Risks in Car-to-Pedestrian Impacts

In vehicle–pedestrian collisions, lower extremities of pedestrians are frequently injured by vehicle front structures. In this study, a finite element (FE) model of THUMS (total human model for safety) was modified in order to assess injuries to a pedestrian lower extremity. Dynamic impact responses of the knee joint of the FE model were validated on the basis of data from the literature. Since in real-world accidents, the vehicle bumper can impact the lower extremities in various situations, the relations between lower extremity injury risk and impact conditions, such as between impact location, angle, and impactor stiffness, were analyzed. The FE simulation demonstrated that the motion of the lower extremity may be classified into a contact effect of the impactor and an inertia effect from a thigh or leg. In the contact phase, the stress of the bone is high in the area contacted by the impactor, which can cause fracture. Thus, in this phase the impactor stiffness affects the fracture risk of bone. In the inertia phase, the behavior of the lower extremity depends on the impact locations and angles, and the knee ligament forces become high according to the lower extremity behavior. The force of the collateral ligament is high compared with other knee ligaments, due to knee valgus motions in vehicle-pedestrian collisions.

SAFER TRUCK FRONT DESIGN FOR PEDESTRIAN IMPACTS

Truck and bus frontal impacts account for a major proportion of pedestrian fatalities in many less motorized countries. To understand this phenomenon, we have collected injury data on pedestrian impacts with buses and trucks and performed computer simulations to identify critical design parameters at 15–45 km/h impact velocities for further investigation. A male dummy which was scaled to fifty percentile Indian dimensions has been used for simulations using MADYMO. Bumper height, bumper offset and grille inclination affect the pelvis and thorax forces and Head Injury Criterion values critically. Bumper width has less effect. Simulations were performed to optimize for the above–mentioned three parameters. Changes in front geometric parameters reduce injury to the upper body and head below safety limits for the existing force–displacement properties but do not affect leg injuries significantly. Hence bumpers need to be made less stiff. Injury data shows that pedestrians also sustain tibia fractures in bus/truck impacts in apparent low velocity impacts. The computer modeling does not offer adequate explanation for this phenomenon. These simulations confirm that it is theoretically possible to make truck/bus fronts safer for pedestrians in impacts up to 35 km/h.

The behavior of bicyclists in frontal and rear crash accidents with cars

Our previous report concerned an analysis of bicyclists struck laterally by cars, which is the most fatal type of accident. The current study compares the behavior of bicyclists struck frontally and from the rear by cars. Comparatively few bicyclist fatalities occur in frontal crash accidents. The comparison is based on accident analysis and MADYMO simulations using a humanlike model. Bicyclist impact behavior was made clear on the basis of computer simulations. It was found that the initial impact between a bicyclists knee and the vehicle front structure is very important in reducing the impact velocity of the bicyclists head.

Human biomechanics and injury prevention

Perspectives on Impact Biomechanics from Traffic Accident Analysis.- Biomechanics and Its Impact on Human Life: From Gene Expression to Organ Physiology.- Recent Advances in the Biomechanics of the Head and Neck.- The Tibia Index: A Step in the Right Direction.- The Biomechanics of Frontal and Lateral Collision.- Influence of Human Spinal Deformation on Minor Neck Injuries for Low Speed Rear Impacts.- Hybrid Approach to Modelling of Biomechanical Systems.- Current Status of Finite Element Human Model Using PAM-CRASH.- Finite Element Model for Simulation of Muscle Effects on Kinematic Responses of Cervical Spine in Low-Speed Rear-End Impacts.- A Biomechanical P.E.E.E.P. Show.- The Development of Chest Protection.- The Activities and Research Projects of the Ministry of Transport and Traffic Safety & Nuisance Research Institute.- Optimized Belt Systems for Front and Rear Seat Passengers.- Development of a Finite Element Model of the Human Lower Extremity for Assessing Automotive Crash Injury Potential.- Development of a Human Ankle/Foot Model.- The Behavior of Bicyclist in Accidents with Cars.- Mechanical Influences on Skeletal Regeneration.- Soft Tissues and Their Functional Repair.- An Application of the Pipette Technique to the Measurement of Local Mechanical Properties of Aortic Walls.- Locations of Bone Formation Change According to the Waveform of Loads - Hypothetic Mechanism of Cells to Detect Mechanical Environment of Bone.- Active Stress Models of Cardiac Muscle, Smooth Muscle and Skeletal Muscle.- Development of High-Speed Tensile Test System for Ligaments and Skeletal Muscles.- Developments in the Provision of Wheelchairs and Seating in Tayside, Scotland.- Bringing Advances in Wheelchairs to the People Who Need Them.- One Basic Research Approach for Assistive Technology in Japan.- Some Mechanical Problems to Use Electric Wheelchairs at a Snowy Region.- Estimation of Lower Limb Muscle Function from Kinematic Gait Analysis and Muscle Tension Model.- A New Force Limitation Mechanism for Risk Reduction of Rehabilitation Robots.- Computational Rehabilitation Engineering with a Walking Model Fine-tuning the Reconstruction of the Anterior Cruciate Ligament in the Knee.- Biomechanics of the Soft Tissue in Repetitive Motion Disorders.- Biotribological Aspects of Natural Synovial Joints and Artificial Joints.- Fundamental Study of Dynamic Analysis of Lumbar Vertebrae.- A Study on Development of the Total Hip Prosthesis Design Fitted for Japanese Patients with Secondary Osteoarthrosis.- Mechanical Functions of Human ACL Bundles: Development and Application of a Robotic Knee Simulator.- Mechanical Properties of Impacted Human Morsellised Cansellous Allografts for Revision Joint Arthroplasty.

Development of High-Speed Tensile Test System for Ligaments and Skeletal Muscles

Although the effects of strain rate on the mechanical properties of ligaments and tendons has been one of the most popular subjects of investigation, many issues remain to be clarified. Moreover the strain rate conditions in most studies were not fast enough for the examination of injury prevention in traffic accidents. As for skeletal muscle, only a few dynamic tensile tests have been done, but the mechanical properties of activated skeletal muscle have not been studied. With this as a background, the purpose of the current study is to develop a new tensile test system to evaluate the mechanical properties of ligaments and skeletal muscles at various strain rates and to perform preliminary tests to evaluate the effects of strain rate. We designed a new hybrid type tensile tester which has an AC servomotor for quasi-static tests and a N2 gas actuator for high-speed tests. The results of preliminary experiments with MCL showed the stress-strain curves to be almost linear for tensile velocities between 0.01 and 10 mm/sec. However, the stress-strain curves changed drastically into a convex shape under high-speed condition. As for the tibialis anterior muscle, the failure sites were mainly the muscle-tendon junction (MTJ) in an active state, in contrast to the muscle belly in a passive state. At 200 mm/sec tensile velocity, failure stress in the active state was greater than that in the passive state.

New Biofidelic Corridor and Biofidelity Test Procedure for Pedestrian Legform Impactors

The objectives of this research are to propose a new impact response corridor for the ISO legform impactor and to determine the biofidelity of the current legform impactor with rigid leg and thigh developed by the Transport Research Laboratory (TRL). The latest data obtained from Post Mortem Human Subject (PMHS) knee impact tests were analyzed in connection with the proposal, and biofidelity legform impact tests were conducted using the current rigid legform impactor. New normalized biofidelic corridors of impact force corresponding to adult male 50th percentile (AM50) are proposed. The impact test results indicate the current rigid legform impactor does not have sufficient human knee biofidelity. The present results suggest that human tolerance can not be used directly for the injury reference value of the legform impactor. A conversion method is needed to interpret the data measured by current legform impactors as the injury reference value.