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

Rib fractures under anterior–posterior dynamic loads: Experimental and finite-element study

This paper discusses lower limb injury impacts to pedestrians. Previous lateral knee bending and shear tests have reported knee joint failure moments close to failure bending moments for the tibia and femur. Eight tibias, eight femurs and three knee joints were tested in lateral bending and two knee joints were tested in lateral shear. Seven previous studies on femur bending, five previous studies on tibia bending, two previous studies on knee joint bending, and one on shear were reviewed and compared with the current tests. All knee joint failures in the current study were either epiphysis fractures of the femur or soft tissue failures. The current study reports an average lateral failure bending moment for the knee joint (134 Nm SD 7) that is dramatically lower than that reported in the literature (284-351 Nm), that reported in the current study for the tibia (291 Nm SD 69) and for femur (382 Nm SD 103). While this research has demonstrated the importance of realistic boundary conditions, more research is necessary to determine a statistically valid impact threshold for the knee joint.

Experiments for establishing pedestrian-impact lower limb injury criteria

This article reviews the attributes of the human surrogates most commonly used in injury biomechanics research. In particular, the merits of human cadavers, human volunteers, animals, dummies, and computational models are assessed relative to their ability to characterize the living human response and injury in an impact environment. Although data obtained from these surrogates have enabled biomechanical engineers and designers to develop effective injury countermeasures for occupants and pedestrians involved in crashes, the magnitude of the traffic safety problem necessitates expanded efforts in research and development. This article makes the case that while there are limitations and challenges associated with any particular surrogate, each provides a critical and necessary component in the continued quest to reduce crash-related injuries and fatalities.

Human surrogates for injury biomechanics research.

The goal of the current study was to perform dynamic bending experiments on legs and thighs from post mortem human surrogates (PMHS) and combine the failure data with that of previous applicable studies to perform an injury risk analysis. Four leg and 12 thigh specimens were loaded dynamically (∼1.5 m/s) in latero-medial 3-point bending. The four leg specimens and six of the thigh specimens were loaded at the mid-diaphysis and the other 6 thigh specimens were loaded at a third of the length from the distal end. Data from four other studies were used with data from the current study to develop injury risk functions for the human thigh loaded at the distal third (50% probability of femur fracture = 372 Nm), and at the mid shaft (50% probability of femur fracture = 447 Nm) and for the human leg loaded at the mid shaft (50% probability of tibia fracture = 312 Nm).

Tolerance of the human leg and thigh in dynamic latero-medial bending

A primary function of pedestrian dummies is biofidelic representation of whole body kinematics. To assess the biofidelity of a pedestrian dummy, corridors for the kinematic response of post-mortem human surrogates (PMHSs) tested in full-scale pedestrian impact tests were developed. Three PMHSs were tested in full-scale pedestrian impact tests using a late-model small sedan with an impact velocity of 40 km/h. Three additional tests using the Polar-II dummy were conducted in identical conditions to those used in the PMHS tests. All impacts were conducted with the PMHS or dummy positioned laterally at the center line of the vehicle, in a mid-stance gait position, with the struck-side limb positioned posteriorly and the upper limbs placed anterior to the torso. Initially supported by a harness, each surrogate was released prior to impact and was unconstrained through a 250 ms interaction with the vehicle. Using photo targets mounted at the equivalent locations of the head center of gravity (CG), top of the thorax, thorax CG, and pelvis CG, the kinematic response of the pedestrian surrogates was evaluated using parametric trajectory data. To account for simultaneous variability in multiple kinematic parameters, boxed-corridors based on a percentage of trajectory path length were developed from the trajectory data. Given the significance of head impact for pedestrian injury outcome, head velocity-time corridors were also developed. Comparing dummy response and PMHS corridors, the Polar-II generally replicated the complex kinematics of the PMHS and demonstrated good overall biofidelity. Greater sliding up the hood by the PMHS, and lack of neck muscle tension in the PMHS have been identified as potential causes for differences in the length and shape of body segment trajectories. More testing is necessary to assess the effects differences in pre-test orientation, surrogate stature, and clothing will have on surrogate response.

Jason R. Kerrigan

Papers

Rib fractures under anterior–posterior dynamic loads: Experimental and finite-element study

Experiments for establishing pedestrian-impact lower limb injury criteria

Human surrogates for injury biomechanics research.

Tolerance of the human leg and thigh in dynamic latero-medial bending

Kinematic Corridors for PMHS Tested in Full-Scale Pedestrian Impact Tests