1. Introduction and Overview. 2. Detecting Influential Observations and Outliers. 3. Detecting and Assessing Collinearity. 4. Applications and Remedies. 5. Research Issues and Directions for Extensions. Bibliography. Author Index. Subject Index.

Regression Diagnostics: Identifying Influential Data and Sources of Collinearity

Abbreviated Injury Scale

We show that the nonlinear mechanical response of networks formed from un–cross-linked fibrin or collagen type I continually changes in response to repeated large-strain loading. We demonstrate that this dynamic evolution of the mechanical response arises from a shift of a characteristic nonlinear stress–strain relationship to higher strains. Therefore, the imposed loading does not weaken the underlying matrices but instead delays the occurrence of the strain stiffening. Using confocal microscopy, we present direct evidence that this behavior results from persistent lengthening of individual fibers caused by an interplay between fiber stretching and fiber buckling when the networks are repeatedly strained. Moreover, we show that covalent cross-linking of fibrin or collagen inhibits the shift of the nonlinear material response, suggesting that the molecular origin of individual fiber lengthening may be slip of monomers within the fibers. Thus, a fibrous architecture in combination with constituents that exhibit internal plasticity creates a material whose mechanical response adapts to external loading conditions. This design principle may be useful to engineer novel materials with this capability.

https://www.pnas.org/content/pnas/110/30/12197.full.pdf

Strain history dependence of the nonlinear stress response of fibrin and collagen networks

Anterior cruciate ligament reconstruction is a frequently performed orthopaedic procedure. Although short-term results are generally good, long-term outcomes are less favorable. Thus, there is renewed interest in improving surgical techniques. Recent studies of anterior cruciate ligament anatomy and function have characterized the 2-bundle structure of the native ligament. During non-weightbearing conditions, the anteromedial (AM) and posterolateral (PL) bundles display reciprocal tension patterns. However, during weightbearing, both the AM and PL bundles are maximally elongated at low flexion angles and shorten significantly with increasing knee flexion. Conventional single-bundle reconstruction techniques often result in nonanatomic tunnel placement, with a tibial PL to a femoral “high AM” tunnel position. In vitro studies have demonstrated that these nonanatomic single-bundle reconstructions cannot completely restore normal anterior-posterior or rotatory laxity. Cadaveric studies suggest that anatomic ...

Anatomic Single- and Double-Bundle Anterior Cruciate Ligament Reconstruction, Part 1: Basic Science

The objective of this study was to develop full body CAD geometry of a seated 50th percentile male. Model development was based on medical image data acquired for this study, in conjunction with extensive data from the open literature. An individual (height, 174.9 cm, weight, 78.6 ± 0.77 kg, and age 26 years) was enrolled in the study for a period of 4 months. 72 scans across three imaging modalities (CT, MRI, and upright MRI) were collected. The whole-body dataset contains 15,622 images. Over 300 individual components representing human anatomy were generated through segmentation. While the enrolled individual served as a template, segmented data were verified against, or augmented with, data from over 75 literature sources on the average morphology of the human body. Non-Uniform Rational B-Spline (NURBS) surfaces with tangential (G1) continuity were constructed over all the segmented data. The sagittally symmetric model consists of 418 individual components representing bones, muscles, organs, blood vessels, ligaments, tendons, cartilaginous structures, and skin. Length, surface area, and volumes of components germane to crash injury prediction are presented. The total volume (75.7 × 103 cm(3)) and surface area (1.86 × 102 cm(2)) of the model closely agree with the literature data. The geometry is intended for subsequent use in nonlinear dynamics solvers, and serves as the foundation of a global effort to develop the next-generation computational human body model for injury prediction and prevention.

Development of a full body CAD dataset for computational modeling: a multi-modality approach

The goal of this study was to determine the detailed design of a greenhouse structure (roof and pillars), such that when it is loaded in a static roof crush test the force-displacement response mimics that of a modern full-size crossover vehicle. This study was carried out using finite element analysis with the goal of identifying a specific design to be fabricated for use with a rollover test buck in dynamic rollover crash testing. A multi-tiered design approach was used consisting first of a simple beam element model, followed by a more complex model meshed with shell and solid elements. A truss-like structure consisting of steel tubing for the pillars, headers and roof rails, connected by steel bars (“plastic joints”) at the intersections was used for the initial design. Individual structure parameters (tubing cross-sections, wall thicknesses, material types, etc.) that did not affect the overall geometry were optimized in repeated simulations of a static roof crush test to ensure that the response of the buck roof matched the response defined by a strength-to-weight ratio of 4.0 for a 2268 kg vehicle. Additionally, different design solutions were examined, e.g. curving the B-pillar, adding a windshield or roof cross beams. The influence of the friction coefficient between the loading platen and the roof was also investigated. Model predictions were validated on component-level by comparing model behavior to three-point bending tests on the plastic joints. The resulting design, including curved B-pillars with additional stiffness elements, was then subjected to a dynamic rollover computer simulation to facilitate qualitative evaluation of the dynamic response in a rollover crash. Further modification of the design may be necessary to improve the response beyond the peak quasi-static test force, but full scale fabrication and testing will be performed first to examine actual response at these levels before implementing additional changes.

Design of a deformable vehicle roof structure for rollover crash testing with a test buck

A mathematical model of the lower extremity was developed, capable of predicting injury risk and simulating the kinetic and kinematic response of the pedestrian lower extremity under vehicle impact loading. The hip-to-foot multi-body model incorporates a detailed facet contact surface, 50th percentile male anthropometric and inertial properties, and stiffness and failure tolerances from the most recent literature. Model validation was achieved using a combination of parameter optimization for component-level kinetic response and full-scale simulations for kinematic response. The three-dimensional kinematic response of the struck-side lower extremity of seven post-mortem human surrogates struck laterally by a sedan at 40 km/h is also presented. For the covering abstract see ITRD E144229.

A new detailed multi-body model of the pedestrian lower extremity: development and preliminary validation

Given the frequency and severity of cervical spine injuries resulting from rollover crashes, it is critical to analyze the mechanism of cervical spine injury in this loading condition. In rollover crashes, roof-to-ground impacts can generate axial compression of the cervical spine, which can result in paralysis and death. This study was performed to compare injury type and severity between component and full body inverted vertex impact tests with post-mortem human surrogates (PMHS); a secondary aim was to determine how changes in vertebral kinematics resulted in changes in hear reaction loads. Five PMHS were suspended in an inverted seated position and then dropped from two heights to achieve 2 m/s (one subjects once and another twice) and 4.4 m/s (all subjects) at impact. The subjects were dropped on a padded five-axis load cell to record the reaction force from impact. Each PMHS was instrumented with three blocks (each containing three accelerometers and three angular rate sensors) rigidly mounted along the upper thoracic spine and on the head. Injuries were determined using both CT scans and dissection following testing. Vertical force traces from the load cell reflect a similar two peak shape seen in previous full-body and component tests. High-speed (1000 Hz) X-ray video analysis shows the neck retains in its initial orientation but becomes increasingly compressed during the loading portion of the first peak. At the first peak, the cervical spine begins to curve, putting the cervical spine into extension, with the center of curvature around C3 or C4, and continues into bending during the unloading of the first peak. The head then translates forward and the neck moves into flexion during the second peak. Each PMHS achieved a flexion injury in the upper thoracic spine or the lower cervical spine during the testing, which occurred during the second peak of the force trace, contradicting previous theories that injury occurs at the first peak, where maximum force occurs. These tests suggest that the direction of torso loading, impact velocity, and boundary conditions at the ends of the cervical spine all affect the kinematics during impact as well as the resulting injuries, and should all be taken into account when determining appropriate injury criteria and developing biofidelic ATDs to predict injuries in crash tests.

Jason R. Kerrigan

Papers

Design of a deformable vehicle roof structure for rollover crash testing with a test buck

A new detailed multi-body model of the pedestrian lower extremity: development and preliminary validation

Injuries and Kinematics: Response of the Cervical Spine in Inverted Impacts

Experimental and computational investigation of human clavicle response in anterior-posterior bending loading

Traumatic brain injury in pedestrian-vehicle collisions: Convexity and suitability of some functionals used as injury metrics.