Biomedical subjects

Lawrence W Schneider

Publications and source records attributed to Lawrence W Schneider.

9 recordsLinked to original sources

PubMed2006

The effects of tethering rear -facing child restraint systems on ATD responses.

A series of sled tests was performed to analyze the responses of an anthropomorphic test device (ATD), particularly neck forces, when rear-facing child restraint systems (CRS) are tethered. Nominally identical rear-facing CRS were tested in four tether conditions: untethered, tethered down to the floor, tethered down to the bottom of the vehicle seat, and tethered rearward to a point above the back of the vehicle seat. The CRABI 12MO ATD with head, upper neck, and chest instrumentation was used in all tests. The tests were conducted using the ECE R44.02 test bench. Both frontal and rear impacts were performed and each condition was repeated for a total of 16 sled tests. Motions of the CRS and ATD were recorded using high-speed digital video (1000 fps). The highest ATD accelerations, forces, and moments were observed during the primary impact of a frontal test, rather than on rebound. The loads observed during rebound from frontal impact were similar in magnitude to the peak loads collected during rear impact. The four tethering geometries produced distinct loading patterns. The lowest HIC, neck forces, and chest accelerations in both impact directions were observed with the rearward tether. The upper neck moment data did not show a clear trend relative to tethering geometry. ATD and CRS motions were best controlled in frontal impact by the rearward tethering geometry while the motions in rear impact were best controlled by tethering to the floor. The data show a potential benefit in both frontal and rear impacts of tethering rear-facing CRS to a point above the vehicle seatback.

Anthropometry↗

PubMed2005

Development of ATD Installation Procedures Based on Rear-Seat Occupant Postures.

The initial positioning of anthropomorphic test devices (ATDs) can influence the outcomes of crash tests. Current procedures for positioning ATDs in rear seats are not based on systematic studies of passenger postures. This paper compares the postures of three side-impact ATDs to the postures of 24 men and women in three vehicle rear seats and 16 laboratory conditions. When positioned using current procedures, the locations of the ES-2 and SID-HIII ATD heads are generally rearward of those observed with similar-size passengers. The SID-IIs head locations matched the expected locations of heads of passengers of similar size more closely. As the seat back angle was increased, people reclined less than the ATDs. Based on these findings, a new ATD positioning procedure for rear seats was developed. The primary objective of the new procedure is to place the ATD head in the location that is most likely for people of similar size. Linear regression equations specify the fore-aft location of the ATD hips and head with respect to the seat H-point as a function of seat back angle (SAE A40) and seat cushion length. The new procedures have been tested with the SID-HIII, ES-2, and SID-IIs side impact ATDs, but are also applicable to frontal impact testing.

Journal Article↗

PubMed2004

Injuries to the hip joint in frontal motor-vehicle crashes: biomechanical and real-world perspectives.

Hip fractures and dislocations in frontal crashes are of substantial concern to clinicians and automotive safety engineers because of the frequency at which hip injuries occur and the associated potential for long-term disability. Impacts to the flexed knees of unembalmed cadavers under loading conditions similar to those that occur in frontal crashes of newer-model vehicles indicate that the hip is the weakest part of the knee-thigh-hip complex and that hip injury tolerance is reduced by hip flexion and adduction from a typical driving posture. These results are being used to develop new knee-thigh-hip injury assessment criteria for use in anthropomorphic test devices (crash test dummies).

Accidents, Traffic↗

PubMed2004

Cervical spine geometry in the automotive seated posture: variations with age, stature, and gender.

In the mid 1970s, UMTRI investigated the biomechanical properties of the head and neck using 180 "normal" adult subjects selected to fill eighteen subject groups based on age (young, mid-aged, older), gender, and stature (short, medium, and tall by gender). Lateral-view radiographs of the subjects' cervical spines and heads were taken with the subjects seated in a simulated automotive neutral posture, as well as with their necks in full-voluntary flexion and full-voluntary extension. Although the cervical spine and lower head geometry were previously measured manually and documented, new technologies have enabled computer digitization of the scanned x-ray images and a more comprehensive and detailed analysis of the variation in cervical spine and lower head geometry with subject age, stature, and gender. After scanning the radiographic images, 108 skeletal landmarks on the cervical vertebrae and 10 head landmarks were digitized. The resulting database of cervical spine and head geometry was used to study cervical spine curvature, vertebral dimensions, and head/neck orientation as functions of age, gender, and stature. The data were used to characterize neutral posture cervical spine curvatures using two methods: a curvature index and Bézier spline functions. Lateral-view vertebral dimensions were also calculated for each subject, and a cascading series of equations was developed to estimate vertebral size and shape for a selected age, stature, and gender. The orientation of the cervical spine was defined using a neck chord angle, where the neck chord was varied to use different anatomical landmarks and estimates of joint centers for the top and bottom of the neck chord. Results from the study have been incorporated into a MS-Access based software package that allows researchers and modelers to generate cervical spine geometries for occupants of a specified age, gender, and stature. The program allows selection of individual occupants from the database that meet age, stature, gender, or curvature criteria, or creation of a composite cervical spine geometry representative of the selected age, gender, and stature. This tool will allow researchers to configure and vary cervical spine geometry in computer models and experimental test setups used to study head and neck impact response and injury risk.

Journal Article↗

PubMed2003

Effects of hip posture on the frontal impact tolerance of the human hip joint.

The pattern of left- and right-side hip injuries to front-seat occupants involved in offset and angled frontal crashes suggests that hip posture (i.e., the orientation of the femur relative to the pelvis) affects the fracture/dislocation tolerance of the hip joint to forces transmitted along the femur during knee-to-knee-bolster loading in frontal impacts. To investigate this hypothesis, dynamic hip tolerance tests were conducted on the left and right hips of 22 unembalmed cadavers. In these tests, the knee was dynamically loaded in the direction of the long axis of the femur and the pelvis was fixed to minimize inertial effects. Thirty-five successful hip tolerance tests were conducted. Twenty-five of these tests were performed with the hip oriented in a typical posture for a seated driver, or neutral posture, to provide a baseline measure of hip tolerance. The effects of hip posture on hip tolerance were quantified using a paired-comparison experimental design. In six pairs of tests, one side of each cadaver was tested with the hip joint oriented in the neutral posture and the contralateral hip from the same cadaver was tested with the hip joint adducted 10 degrees from the neutral posture. In four pairs of tests, the hip was tested in neutral and 30 degrees flexed postures. The average fracture tolerance of the hip in the neutral posture was 6.1-/+1.5 kN. Hip tolerance decreased by an average of 34-/+4% with 30 degrees of flexion from the neutral posture (p<0.0001) and by 18-/+8% with 10 degrees of adduction from the neutral posture (p=0.008).

Journal Article↗

PubMed2003

Biomechanics of 4-point seat belt systems in frontal impacts.

The biomechanical behavior of 4-point seat belt systems was investigated through MADYMO modeling, dummy tests and post mortem human subject tests. This study was conducted to assess the effect of 4-point seat belts on the risk of thoracic injury in frontal impacts, to evaluate the ability to prevent submarining under the lap belt using 4-point seat belts, and to examine whether 4-point belts may induce injuries not typically observed with 3-point seat belts. The performance of two types of 4-point seat belts was compared with that of a pretensioned, load-limited, 3-point seat belt. A 3-point belt with an extra shoulder belt that "crisscrossed" the chest (X4) appeared to add constraint to the torso and increased chest deflection and injury risk. Harness style shoulder belts (V4) loaded the body in a different biomechanical manner than 3-point and X4 belts. The V4 belt appeared to shift load to the clavicles and pelvis and to reduce traction of the shoulder belt across the chest, resulting in a reduction in chest deflection by a factor of two. This is associated with a 5 to 500-fold reduction in thoracic injury risk, depending on whether one assumes 4-point belts apply concentrated or distributed load. In four of six post mortem human subjects restrained by V4 belts during 40 km/h sled tests, chest compression was zero or negative and rib fractures were nearly eliminated. Submarining was not observed in any test with post mortem human subjects. Though lumbar, sacral and pelvic injuries were noted, they are believed to be due to the artificial restraint environment (no knee bolsters, instrument panels, steering systems or airbags). While they show significant potential to reduce thoracic injury risk, there are still many issues to be resolved before 4-point belts can be considered for production vehicles. These issues include, among others, potential effects on hard and soft neck tissues, of interaction with inboard shoulder belts in farside impacts and potential effects on the fetus of latch/buckle junctions at the centerline of pregnant occupants. Work continues at Ford Motor Company to resolve these issues.

Journal Article↗

PubMed2002

A statistical method for predicting automobile driving posture.

A new model for predicting automobile driving posture is presented. The model, based on data from a study of 68 men and women in 18 vehicle package and seat conditions, is designed for use in posturing the human figure models that are increasingly used for vehicle interior design. The model uses a series of independent regression models, coupled with data-guided inverse kinematics, to fit a whole-body linkage. An important characteristic of the new model is that it places greatest importance on prediction accuracy for the body locations that are most important for vehicle interior design: eye location and hip location. The model predictions were compared with the driving postures of 120 men and women in five vehicles. Errors in mean eye location predictions in the vehicles were typically less than 10 mm. Prediction errors were largely independent of anthropometric variables and vehicle layout. Although the average posture of a group of people can be predicted accurately, individuals' postures cannot be predicted precisely because of interindividual posture variance that is unrelated to key anthropometric variables. The posture prediction models developed in this research can be applied to posturing computer-rendered human models to improve the accuracy of ergonomic assessments of vehicle interiors.

Adult↗

PubMed2002

Estimating infant head injury criteria and impact response using crash reconstruction and finite element modeling.

A combination of finite element modeling and sled test reconstruction of real-world infant head injury scenarios has been used to investigate infant head impact response and tolerance to skull fracture. Studying the role of cranial sutures on infant skull response was of particular interest. The specific injury scenarios selected for reconstruction involved infants in rear-facing child restraint systems (CRS) who sustained skull fractures and brain injuries from deploying passenger-side frontal airbags. Approximations of the loading conditions for three injury cases, as well as estimates of loading conditions not expected to result in head injury, were produced in the laboratory. A finite element model (FEM) of a six-month-old infant head was developed using available material properties and humanlike geometry. The infant head FEM was used to simulate different injury and no-injury loading conditions based on CRS response data from the reconstruction tests. Acceleration results and stress distributions are consistent with the level of injury in the different real-world cases. Cranial sutures have a negligible effect on stress distribution in the infant skull. Logistic regression analysis was used to estimate threshold stresses associated with skull fracture. The acceleration responses of the infant head FEM and the CRABI ATD were compared for the no-injury and injury-producing conditions. Results suggest that the biofidelic loading range of the CRABI ATD may be limited to impacts at or below injury-producing loading severities. Provisional injury assessment reference values corresponding to the threshold for minor skull fracture over a limited loading range were estimated for the current CRABI ATD, and recommended improvements for the CRABI ATD head are presented.

Journal Article↗

PubMed2002

The tolerance of the human hip to dynamic knee loading.

Based on an analysis of the National Automotive Sampling System (NASS) database from calendar years 1995-2000, over 30,000 fractures and dislocations of the knee-thigh-hip (KTH) complex occur in frontal motor-vehicle crashes each year in the United States. This analysis also shows that the risk of hip injury is generally higher than the risks of knee and thigh injuries in frontal crashes, that hip injuries are occurring to adult occupants of all ages, and that most hip injuries occur at crash severities that are equal to, or less than, those used in FMVSS 208 and NCAP testing. Because previous biomechanical research produced mostly knee or distal femur injuries, and because knee and femur injuries were frequently documented in early crash investigation data, the femur has traditionally been viewed as the weakest part of the KTH complex. However, the relative risk of hip injuries to the risks of knee and thigh injuries in frontal crashes of late-model vehicles suggests that this may not be the case. This study investigated the frontal-impact fracture tolerance of the hip in nineteen tests performed on the KTH complexes from sixteen unembalmed human cadavers. In each test, the pelvis was rigidly fixed by gripping the iliac wings with the thigh-to-pelvis angle set to correspond to a standard automotive-seated posture. A dynamic load was applied to the knee along the axis of the femur at loading rates that are representative of knee-to-knee bolster impacts in frontal crashes. Rigidly fixing the pelvis minimizes inertial effects along the KTH complex, which results in similar force levels along the KTH complex. Consequently, in these tests, the weakest part of the KTH complex failed first. All seventeen fixed pelvis tests that produced usable data resulted in acetabular fractures at an average applied force of 5.70 kN (sd = 1.38 kN). The lack of injuries to the femoral shaft and distal femur in these tests indicates that the tolerance of the hip is less than that of the femur under frontal-impact loading. To further explore the tolerance of the femur relative to the hip, thirteen uninjured knee/femur specimens from seven cadavers previously used in hip tolerance tests were dynamically loaded. In these tests, the head of the femur was supported in a fixed "acetabular cup" to minimize inertial effects, and load was applied at the knee along the axis of the femur. All of these tests resulted in femoral neck fractures. Two tests also resulted in fractures to the femoral shaft. The average tolerance of the femoral neck from these tests is 7.59 kN (sd = 1.58 kN), which is significantly higher (p < 0.05) than the tolerance of the acetabulum. These results suggest that the mid and distal portions of the femur have a higher tolerance under these loading conditions than the pelvic and femoral portions of the hip.

Journal Article↗