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

Obesity is associated with an increased fatality risk in automobile collisions. The goal of this study was to evaluate the predictive capabilities of the obese human body models via comparison of model simulations to post‐mortem human subject tests from the literature. First, obese post‐mortem human subject sled tests were used to assess the ability of the obese GHBMC models to replicate occupant kinematics in a sled environment. Second, lap belt pull tests were used to evaluate belt interaction with the abdomen and pelvis. Third, adipose tissue‐level tests were used to evaluate the shear stiffness of the flesh material model used in the obese human body models. Similar to the post‐mortem human subject tests, the obese human body models experienced substantial lower extremity forward motion in the sled test simulations. However, the model did not exhibit submarining behaviour as observed in the post‐mortem human subject experiments. Further, the lap belt pull simulations failed to reproduce the belt/abdomen interaction seen in the post‐mortem human subject, and the material model used to represent the human body model flesh was found to be approximately one order of magnitude stiffer than human abdominal subcutaneous adipose tissue. This study shows that improved models of abdominal flesh, and specifically subcutaneous adipose tissue, may be required to obtain biofidelic belt/abdomen interactions and to predict submarining behaviour in crash simulations.

Performance of the obese GHBMC models in the sled and belt pull test conditions

This study compares head impact dynamics between post-mortem human surrogates (PMHS) and the Polar-II pedestrian crash dummy in vehicle–pedestrian impacts with a small sedan and a large sports utility vehicle (SUV). A total of 15 (8 sedan and 7 SUV) full-scale vehicle pedestrian impact tests were performed at 40 km/h. For each vehicle, two (SUV) or three (sedan) PMHS tests and five dummy tests were performed, with three of the dummy tests in the same configuration to show repeatability, and the other two tests utilising slightly different configurations. Head linear and angular kinematics were captured from PMHS and dummy head instrumentation, and dummy upper neck load cell data were used to determine neck forces and calculate head impact forces. Differences in head impact locations, timing and kinematics between the dummy and PMHS were minimised when the dummy was positioned higher above the ground reference level to match the pelvis height of the PMHS. On average, the dummy recorded higher resultant impact forces (2930 N vs. 1862 N) in windshield impacts to the sedan than in hood impacts to the SUV, which resulted in higher 15-ms Head Injury Criteria (HIC15) values and higher peak and averaged angular accelerations. While there are differences in dummy injury risk metrics, both the dummy and PMHS data show that the difference in injury risk metrics predicted by the dummy can be explained by the variation in impact velocity between the sedan (14.1 ± 1.2 m/s) and the SUV (10.7 ± 2.3 m/s), the differences in injury risk predicted by the PMHS are not as clear due to confounding factors. The data and analyses presented in this study also show that neck forces during head impacts contribute a substantial and additive effect to the head impact accelerations (and thus HIC15 values) measured in the dummy, and that for the SUV, neck forces affect head accelerations more than impact forces. Despite analysing only lateral impacts with two vehicle geometries at 40 km/h, this study provides the only comparison of PMHS and dummy pedestrian head impact kinematics data available.

Assessment of pedestrian head impact dynamics in small sedan and large SUV collisions

A new approach to multibody model development: pedestrian lower extremity.

Road traffic injuries could become the fifth leading cause of death globally by 2030 unless appropriate countermeasures are taken. Reliable reconstruction of collisions is essential for understandi...

Predictive capabilities of the MADYMO multibody pedestrian model: Three-dimensional head translation and rotation, head impact time and head impact velocity:

Current standards and test devices for pedestrian safety are developed using results from impact tests where inertial considerations have dominated and the vehicle pedestrian loading environment has not been properly replicated. When controlled tests have been conducted to evaluate the biofidelity of anthropometric test devices, current designs have faired poorly. The objective of the current study was to develop dynamic force-deflection and moment-deflection response corridors for the 50 th percentile adult male thigh and leg subjected to non-midpoint 3-point bending at rates characteristic of the vehicle-pedestrian loading environment. Six thigh and eight leg specimens were harvested from eight adult male human cadavers and ramped to failure in dynamic 3-point bending in the latero-medial direction. All thigh specimens and four of the leg specimens were loaded at a point located one third of the femoral/tibial length from the distal end, whereas the point of load application for the remaining four leg specimens was at one third of the tibial length from the proximal end. Following geometrical scaling of the structural responses to the size of the 50 th percentile adult male, force-deflection and moment-deflection response corridors were determined using a procedure specifically designed for developing corridors from sets of individual responses for which the independent variable is displacement. The corridors provide necessary information for development and validation of mechanical and computational tools for evaluation of countermeasures for pedestrian lower extremity protection.

Jason R. Kerrigan

Papers

Performance of the obese GHBMC models in the sled and belt pull test conditions

Assessment of pedestrian head impact dynamics in small sedan and large SUV collisions

A new approach to multibody model development: pedestrian lower extremity.

Predictive capabilities of the MADYMO multibody pedestrian model: Three-dimensional head translation and rotation, head impact time and head impact velocity:

Dynamic Response Corridors of the Human Thigh and Leg in Non-Midpoint Three-Point Bending