Evaluation of the Foot Arch in Partial Weightbearing Conditions.

BACKGROUND: Weightbearing plain radiography or computed tomography (CT) is used for diagnosis or treatment selection in foot disorders. This study compared foot alignment between full weightbearing (50% body weight [BW] per foot) plain radiography and nonweightbearing (0% BW) or partial weightbearing (10% BW per foot) CT scans. METHODS: Subjects had both full (50% BW per foot) weightbearing plain radiographs and either a nonweightbearing (0% BW) or a partial weightbearing (20% BW or 10% BW per foot) CT scan. Feet (n = 89) had been previously classified as pes cavus (n = 14/17 [subjects/feet]), neutrally aligned (NA; 20/30), asymptomatic pes planus (APP; 18/24), and symptomatic pes planus (SPP; 15/18). Lateral talometatarsal angle (LTMA) and calcaneal pitch angle were compared between weightbearing radiography and maximum-intensity projection images generated from CT. RESULTS: Significant differences in LTMA were found between nonweightbearing CT scans and full (50% BW per foot) weightbearing plain radiographs: the mean difference was 6.6 degrees in NA, 9.2 degrees in APP, and 11.3 degrees in SPP (P < .0001); no significant difference in LTMA was found for pes cavus. Although the interaction of foot type (P = .084) approached statistical significance, pairwise differences between 10% weightbearing and 50% weightbearing images by foot type were significant but small. The 50% weightbearing condition resulted in calcaneal pitch angles the same or slightly lower or higher than those of the 10% weightbearing and nonweightbearing images. LTMA and calcaneal pitch angle measurements made on full (50% BW per foot) weightbearing plain radiographs and non- (0%) or partial (10% BW per foot) weightbearing angles from CT scans were strongly correlated. CONCLUSION: Different foot types have similar 2-dimensional sagittal plane morphologies with partial weightbearing (10% BW per foot) CT scans and, to a lesser degree, nonweightbearing (0%) neutral-position CT scans when compared to full weightbearing (50% BW per foot) plain radiographs. LEVEL OF EVIDENCE: Level III, retrospective case control study.

Neuropathy, claw toes, intrinsic muscle volume, and plantar aponeurosis thickness in diabetic feet.

BACKGROUND: The objective of this study was to explore the relationships between claw toe deformity, peripheral neuropathy, intrinsic muscle volume, and plantar aponeurosis thickness using computed tomography (CT) images of diabetic feet in a cross-sectional analysis. METHODS: Forty randomly-selected subjects with type 2 diabetes were selected for each of the following four groups (n = 10 per group): 1) peripheral neuropathy with claw toes, 2) peripheral neuropathy without claw toes, 3) non-neuropathic with claw toes, and 4) non-neuropathic without claw toes. The intrinsic muscles of the foot were segmented from processed CT images. Plantar aponeurosis thickness was measured in the reformatted sagittal plane at 20% of the distance from the most inferior point of the calcaneus to the most inferior point of the second metatarsal. Five measurement sites in the medial-lateral direction were utilized to fully characterize the plantar aponeurosis thickness. A linear mixed-effects analysis on the effects of peripheral neuropathy and claw toe deformity on plantar aponeurosis thickness and intrinsic muscle volume was performed. RESULTS: Subjects with concurrent neuropathy and claw toes had thicker mean plantar aponeurosis (p < 0.006) and may have had less mean intrinsic muscle volume (p = 0.083) than the other 3 groups. The effects of neuropathy and claw toes on aponeurosis thickness were synergistic rather than additive. A similar pattern may exist for intrinsic muscle volume, but results were not as conclusive. A negative correlation was observed between plantar aponeurosis thickness and intrinsic muscle volume (R2 = 0.323, p < 0.001). CONCLUSIONS: Subjects with concurrent neuropathy and claw toe deformity were associated with the smallest intrinsic foot muscle volumes and the thickest plantar aponeuroses. Intrinsic muscle atrophy and plantar aponeurosis thickening may be related to the development of claw toes in the presence of neuropathy.

Calibration of the shear wave speed-stress relationship in in situ Achilles tendons using cadaveric simulations of gait and isometric contraction.

It has been shown that shear wave speed is directly dependent on axial stress in ex vivo tendons. Hence, a wave speed sensor could be used to track tendon loading during movement. However, adjacent soft tissues and varying joint postures may affect the wave speed-load relationship for intact tendons. The purpose of this study was to determine whether the proportional relationship between squared wave speed and stress holds for in situ cadaveric Achilles tendons, to evaluate whether this relationship is affected by joint angle, and to assess potential calibration techniques. Achilles tendon wave speed and loading were simultaneously measured during cadaveric simulations of gait and isometric contractions performed in a robotic gait simulator. Squared wave speed and axial stress were highly correlated during isometric contraction at all ankle postures (R2avg = 0.98) and during simulations of gait (R2avg = 0.92). Ankle plantarflexion angle did not have a consistent effect on the constant of proportionality (p = 0.217), but there was a significant specimen-angle interaction effect (p < 0.001). Wave speed-based predictions of tendon stress were most accurate (average RMS error = 11% of maximum stress) when calibrating to isometric contractions performed in a dorsiflexed posture that resembled the posture at peak Achilles loading during gait. The results presented here show that the linear relationship between tendon stress and squared shear wave speed holds for a case resembling in vivo conditions, and that calibration during an isometric task can yield accurate predictions of tendon loading during a functional task.

Hind- and midfoot bone morphology varies with foot type and sex.

Foot type has been associated with pain, injury, and altered gait mechanics. Morphological variations in foot bones due to foot type variation may impact surgical and therapeutic treatments. The purpose of this study was to utilize principal component analysis (PCA) to determine how morphology of the hind- and midfoot bones differs among foot types and sex. The calcaneus, talus, navicular, and cuboid were segmented using previously obtained computed tomography (CT) scans and converted to surface models. The CTs were sorted into four foot types-cavus, neutrally aligned, asymptomatic planus, and symptomatic planus. Morphometric shape analysis software (Geomorph) was used to perform a PCA to determine which components varied between foot types and between sexes. The calcaneus showed planus feet of both types to have calcanei that have decreased height and increased length compared to neutrally aligned feet. The talus demonstrated increased posterior mass for cavus feet compared to neutrally aligned feet. For the navicular, symptomatic planus had a more posteriorly positioned tuberosity and were wider than asymptomatic planus feet. The cuboid did not exhibit any differences between foot types. Sex differences, found only at the talus and navicular, were subtle. PCA is an objective technique that helped elucidate differences in bone morphology between foot types and sex without needing to determine the features of interest before comparing groups. Understanding these variations can help inform diagnosis of foot pathologies and surgical protocols as well as improve computer models of the foot. Published 2018. This article is a U.S. Government work and is in the public domain in the USA. J Orthop Res 9999:1-16, 2019.

Model-based tracking of the bones of the foot: A biplane fluoroscopy validation study.

Measuring foot kinematics using optical motion capture is technically challenging due to the depth of the talus, small bone size, and soft tissue artifact. We present a validation of our biplane X-ray system, demonstrating its accuracy in tracking the foot bones directly. Using an experimental linear/rotary stage we imaged pairs of tali, calcanei, and first metatarsals, with embedded beads, through 30 poses. Model- and bead-based algorithms were employed for semi-automatic tracking. Translational and rotational poses were compared to the experimental stage (a reference standard) to determine registration performance. For each bone, 10 frames per pose were analyzed. Model-based: The resulting overall translational bias of the six bones was 0.058 mm with a precision of ± 0.049 mm. The overall rotational bias of the six bones was 0.42° with a precision of ± 0.41°. Bead-based: the overall translational bias was 0.037 mm with a precision of ± 0.032 mm and for rotation was 0.29° with a precision of ± 0.26°. We validated the accuracy of our system to determine the spatial position and orientation of isolated foot bones, including the talus, calcaneus, and first metatarsal over a range of quasi-static poses. Although the accuracy of dynamic motion was not assessed, use of an experimental stage establishes a reference standard.

Metatarsal Shape and Foot Type: A Geometric Morphometric Analysis.

Planus and cavus foot types have been associated with an increased risk of pain and disability. Improving our understanding of the geometric differences between bones in different foot types may provide insights into injury risk profiles and have implications for the design of musculoskeletal and finite-element models. In this study, we performed a geometric morphometric analysis on the geometry of metatarsal bones from 65 feet, segmented from computed tomography (CT) scans. These were categorized into four foot types: pes cavus, neutrally aligned, asymptomatic pes planus, and symptomatic pes planus. Generalized procrustes analysis (GPA) followed by permutation tests was used to determine significant shape differences associated with foot type and sex, and principal component analysis was used to find the modes of variation for each metatarsal. Significant shape differences were found between foot types for all the metatarsals (p < 0.01), most notably in the case of the second metatarsal which showed significant pairwise differences across all the foot types. Analysis of the principal components of variation showed pes cavus bones to have reduced cross-sectional areas in the sagittal and frontal planes. The first (p = 0.02) and fourth metatarsals (p = 0.003) were found to have significant sex-based differences, with first metatarsals from females shown to have reduced width, and fourth metatarsals from females shown to have reduced frontal and sagittal plane cross-sectional areas. Overall, these findings suggest that metatarsal bones have distinct morphological characteristics that are associated with foot type and sex, with implications for our understanding of anatomy and numerical modeling of the foot.

Robotic-assisted locomotor training enhances ankle performance in adults with incomplete spinal cord injury.

OBJECTIVE: Ankle joint control plays an important role in independent walking. This study investigated the effects of robotic-assisted locomotor training on impaired ankle joint control in individuals with chronic incomplete spinal cord injury. METHODS: Sixteen individuals with incomplete spinal cord injury underwent 12 one-h sessions of robotic-assisted locomotor training for 4 weeks, while 16 individuals with incomplete spinal cord injury served as inactive controls. Changes in ankle control measures, torque and co-activation were evaluated during maximal voluntary contractions in dorsi- and plantar-flexion. Changes in walking performance measures using Timed Up and Go (TUG), 10-m walk (10MWT) and 6-min walk (6MWT) tests were evaluated at 2 time points: baseline and after 4 weeks. RESULTS: Maximal voluntary contractions torque during both dorsi- and plantar-flexion contractions improved markedly in the robotic-assisted locomotor training group compared with baseline. Furthermore, after the training, co-activation during the dorsi-flexion maximal voluntary contractions decreased in the training group compared with controls. In addition, the training group significantly improved walking mobility (TUG) and speed (10MWT) compared with baseline. Finally, correlation analysis indicated a significant linear relationship between maximal voluntary contraction torques and walking performance measures. CONCLUSION: These findings provide evidence that robotic-assisted locomotor training improves ankle joint control, which may translate into enhanced walking performance in individuals with chronic incomplete spinal cord injury.

Micromechanical modeling of calcifying human costal cartilage using the generalized method of cells.

Various tissues in the human body, including cartilage, are known to calcify with aging. There currently is no material model that accounts for the calcification in the costal cartilage, which could affect the overall structural response of the rib cage, and thus change the mechanisms and resistance to injury. The goal of this study is to investigate, through the development of a calcifying cartilage model, whether the calcification morphologies present in the costal cartilage change its effective material properties. A calcified cartilage material model was developed using the morphologies of calcifications obtained from microCT and the relaxed elastic modulus of the human costal cartilage obtained from indentation testing. The homogenized model of calcifying cartilage found that calcifications alter the effective material behavior of the cartilage, and this effect is highly dependent on the microstructural connectivity of the calcification. Calcifications which are not contiguous with the rib bone and constitute 0-18% of the cartilage volume increase the effective elastic modulus from its baseline value of 5MPa to up to 8MPa. Calcifications which are attached to the rib bone, which typically constitute 18-25% of the cartilage volume, result in effective moduli of 20-66MPa, depending on the microstructure, and introduce marked anisotropy into the material. The calcifying cartilage model developed in this study can be incorporated into biomechanical models of the aging thorax to better understand how calcifications in the aging thorax affect the structural response of the rib cage.

Thoracic response targets for a computational model: a hierarchical approach to assess the biofidelity of a 50th-percentile occupant male finite element model.

Current finite element human thoracic models are typically evaluated against a limited set of loading conditions; this is believed to limit their capability to predict accurate responses. In this study, a 50th-percentile male finite element model (GHBMC v4.1) was assessed under various loading environments (antero-posterior rib bending, point loading of the denuded ribcage, omnidirectional pendulum impact and table top) through a correlation metric tool (CORA) based on linearly independent signals. The load cases were simulated with the GHBMC model and response corridors were developed from published experimental data. The model was found to be in close agreement with the experimental data both qualitatively and quantitatively (CORA ratings above 0.75) and the response of the thorax was overall deemed biofidelic. This study also provides relevant corridors and an objective rating framework that can be used for future evaluation of thoracic models.

Effects of robotic-locomotor training on stretch reflex function and muscular properties in individuals with spinal cord injury.

OBJECTIVE: We sought to determine the therapeutic effect of robotic-assisted step training (RAST) on neuromuscular abnormalities associated with spasticity by characterization of their recovery patterns in people with spinal cord injury (SCI). METHODS: Twenty-three motor-incomplete SCI subjects received one-hour RAST sessions three times per week for 4 weeks, while an SCI control group received no training. Neuromuscular properties were assessed using ankle perturbations prior to and during the training, and a system-identification technique quantified stretch reflex and intrinsic stiffness magnitude and modulation with joint position. Growth-mixture modeling classified subjects based on similar intrinsic and reflex recovery patterns. RESULTS: All recovery classes in the RAST group presented significant (p<0.05) reductions in intrinsic and reflex stiffness magnitude and modulation with position; the control group presented no changes over time. Subjects with larger baseline abnormalities exhibited larger reductions, and over longer training periods. CONCLUSIONS: Our findings demonstrate that RAST can effectively reduce neuromuscular abnormalities, with greater improvements for subjects with higher baseline abnormalities. SIGNIFICANCE: Our findings suggest, in addition to its primary goal of improving locomotor patterns, RAST can also reduce neuromuscular abnormalities associated with spasticity. These findings also demonstrate that these techniques can be used to characterize neuromuscular recovery patterns in response to various types of interventions.

Effect of intercostal muscle and costovertebral joint material properties on human ribcage stiffness and kinematics.

Current finite element (FE) models of the human thorax are limited by the lack of local-level validation, especially in the ribcage. This study exercised an existing FE ribcage model for a 50th percentile male under quasi-static point loading and dynamic sternal loading. Both force-displacement and kinematic responses of the ribcage were compared against experimental data. The sensitivity of the model response to changes in the material properties of the costovertebral (CV) joints and intercostal muscles was assessed. The simulations found that adjustments to the CV joints tended to change the amount of rib rotation in the sagittal plane, while changes to the elastic modulus and thickness of the intercostal muscles tended to alter both the stiffness and the direction and magnitude of rib motions. This study can lend insight into the role that the material properties of these two thoracic structures play in the dynamics of the ribcage during a frontal loading condition.

Development of structural and material clavicle response corridors under axial compression and three point bending loading for clavicle finite element model validation.

Clavicle injuries were frequently observed in automotive side and frontal crashes. Finite element (FE) models have been developed to understand the injury mechanism, although no clavicle loading response corridors yet exist in the literature to ensure the model response biofidelity. Moreover, the typically developed structural level (e.g., force-deflection) response corridors were shown to be insufficient for verifying the injury prediction capacity of FE model, which usually is based on strain related injury criteria. Therefore, the purpose of this study is to develop both the structural (force vs deflection) and material level (strain vs force) clavicle response corridors for validating FE models for injury risk modeling. 20 Clavicles were loaded to failure under loading conditions representative of side and frontal crashes respectively, half of which in axial compression, and the other half in three point bending. Both structural and material response corridors were developed for each loading condition. FE model that can accurately predict structural response and strain level provides a more useful tool in injury risk modeling and prediction. The corridor development method in this study could also be extended to develop corridors for other components of the human body.

Prediction of gait recovery in spinal cord injured individuals trained with robotic gait orthosis.

BACKGROUND: Motor impairment is a major consequence of spinal cord injury (SCI). Earlier studies have shown that robotic gait orthosis (e.g., Lokomat) can improve an SCI individual's walking capacity. However, little is known about the differential responses among different individuals with SCI. The present longitudinal study sought to characterize the distinct recovery patterns of gait impairment for SCI subjects receiving Lokomat training, and to identify significant predictors for these patterns. METHODS: Forty SCI subjects with spastic hypertonia at their ankles were randomly allocated to either control or intervention groups. Subjects in the intervention group participated in twelve 1-hour Lokomat trainings over one month, while control subjects received no interventions. Walking capacity was evaluated in terms of walking speed, functional mobility, and endurance four times, i.e. baseline, 1, 2, and 4 weeks after training, using the 10-Meter-Walking, Timed-Up-and-Go, and 6-Minute-Walking tests. Growth Mixture Modeling, an analytical framework for stratifying subjects based on longitudinal changes, was used to classify subjects, based on their gait impairment recovery patterns, and to identify the effects of Lokomat training on these improvements. RESULTS: Two recovery classes (low and high walking capacity) were identified for each clinical evaluation from both the control and intervention groups. Subjects with initial high walking capacity (i.e. shorter Timed-Up-and-Go time, higher 10-Meter-Walking speed and longer 6-Minute-Walking distance) displayed significant improvements in speed and functional mobility (0.033 m/s/week and-0.41 s/week respectively); however no significant change in endurance was observed. Subjects with low walking capacity exhibited no significant improvement. The membership in these two classes-and thus prediction of the subject's gait improvement trajectory over time-could be determined by the subject's maximum voluntary torque at the ankle under both plantar-and dorsi-flexion contractions determined prior to any training. CONCLUSION: Our findings demonstrate that subjects responded to Lokomat training non-uniformly, and should potentially be grouped based on their likely recovery patterns using objective criteria. Further, we found that the subject's ankle torque can predict whether he/she would benefit most from Lokomat training prior to the therapy. These findings are clinically significant as they can help individualize therapeutic programs that maximize patient recovery while minimizing unnecessary efforts and costs.

Robotic-locomotor training as a tool to reduce neuromuscular abnormality in spinal cord injury: the application of system identification and advanced longitudinal modeling.

In this study, the effect of the LOKOMAT, a robotic-assisted locomotor training system, on the reduction of neuromuscular abnormalities associated with spasticity was examined, for the first time in the spinal cord injury (SCI) population. Twenty-three individuals with chronic incomplete SCI received 1-hour training sessions in the LOKOMAT three times per week, with up to 45 minutes of training per session; matched control group received no intervention. The neuromuscular properties of the spastic ankle were then evaluated prior to training and after 1, 2, and 4 weeks of training. A parallel-cascade system identification technique was used to determine the reflex and intrinsic stiffness of the ankle joint as a function of ankle position at each time point. The slope of the stiffness vs. joint angle curve, i.e. the modulation of stiffness with joint position, was then calculated and tracked over the four-week period. Growth Mixture Modeling (GMM), an advanced statistical method, was then used to classify subjects into subgroups based on similar trends in recovery pattern of slope over time, and Random Coefficient Regression (RCR) was used to model the recovery patterns within each subgroup. All groups showed significant reductions in both reflex and intrinsic slope over time, but subjects in classes with higher baseline values of the slope showed larger improvements over the four weeks of training. These findings suggest that LOKOMAT training may also be useful for reducing the abnormal modulation of neuromuscular properties that arises as secondary effects after SCI. This can advise clinicians as to which patients can benefit the most from LOKOMAT training prior to beginning the training. Further, this study shows that system identification and GMM/RCR can serve as powerful tools to quantify and track spasticity over time in the SCI population.

Characterization of the centroidal geometry of human ribs.

While a number of studies have quantified overall ribcage morphology (breadth, depth, kyphosis/lordosis) and rib cross-sectional geometry in humans, few studies have characterized the centroidal geometry of individual ribs. In this study, a novel model is introduced to describe the centroidal path of a rib (i.e., the sequence of centroids connecting adjacent cross-sections) in terms of several physically-meaningful and intuitive geometric parameters. Surface reconstructions of rib levels 2-10 from 16 adult male cadavers (aged 31-75 years) were first extracted from CT scans, and the centroidal path was calculated in 3D for each rib using a custom numerical method. The projection of the centroidal path onto the plane of best fit (i.e., the "in-plane" centroidal path) was then modeled using two geometric primitives (a circle and a semiellipse) connected to give C1 continuity. Two additional parameters were used to describe the deviation of the centroidal path from this plane; further, the radius of curvature was calculated at various points along the rib length. This model was fit to each of the 144 extracted ribs, and average trends in rib size and shape with rib level were reported. In general, upper ribs (levels 2-5) had centroidal paths which were closer to circular, while lower ribs (levels 6-10) tended to be more elliptical; further the centroidal curvature at the posterior extremity was less pronounced for lower ribs. Lower ribs also tended to exhibit larger deviations from the best-fit plane. The rib dimensions and trends with subject stature were found to be consistent with findings previously reported in the literature. This model addresses a critical need in the biomechanics literature for the accurate characterization of rib geometry, and can be extended to a larger population as a simple and accurate way to represent the centroidal shape of human ribs.

Development and validation of a subject-specific finite element model of a human clavicle.

This study aimed to develop and validate a finite element (FE) model of a human clavicle which can predict the structural response and bone fractures under both axial compression and anterior-posterior three-point bending loads. Quasi-static non-injurious axial compression and three-point bending tests were first conducted on a male clavicle followed by a dynamic three-point bending test to fracture. Then, two types of FE models of the clavicle were developed using bone material properties which were set to vary with the computed tomography image density of the bone. A volumetric solid FE model comprised solely of hexahedral elements was first developed. A solid-shell FE model was then created which modelled the trabecular bone as hexahedral elements and the cortical bone as quadrilateral shell elements. Finally, simulations were carried out using these models to evaluate the influence of variations in cortical thickness, mesh density, bone material properties and modelling approach on the biomechanical responses of the clavicle, compared with experimental data. The FE results indicate that the inclusion of density-based bone material properties can provide a more accurate reproduction of the force-displacement response and bone fracture timing than a model with uniform bone material properties. Inclusion of a variable cortical thickness distribution also slightly improves the ability of the model to predict the experimental response. The methods developed in this study will be useful for creating subject-specific FE models to better understand the biomechanics and injury mechanism of the clavicle.

Response of the Worldwide Side Impact Dummy (WorldSID) to Localized Constant-Speed Impacts.

The objective of this study was to evaluate WorldSID constant-speed shoulder and thorax impact responses in terms of impact force, external and internal deflection (1D and 2D IR-Tracc response) for two velocities (1 m/s and 3 m/s), at three impact levels (shoulder, upper thorax and mid thorax) in three impact directions (lateral, +15° posterolateral, -15° anteraolateral). In addition, the impact force and external deflection were compared to previously published cadaver data. Each impact condition was repeated twice. A total of 42 tests were performed. The WorldSID's lowest peak impact force and external deflection were found for impact at shoulder level regardless of impact direction. Maximum force and deflection were found for impact at mid thorax. Comparison between WorldSID and PMHS showed similar external chest deflections for impacts at 3 m/s. The peak impact force response with respect to impact level was found to be reversed for the WorldSID compared to the PMHS, for which shoulder impact resulted in the highest peak force. External time history responses for the WorldSID compared to the one PMHS impacted at 1 m/s in lateral impact direction showed a significant difference in both timing and magnitude. External deflections at upper and mid thorax were approximately twice as high as the internal 1D deflection measured by the IR-Tracc. However, taking into account the rotation of the rib, the calculated 2D deflection response at the posterior impact direction was closer to the external deflection, and thus also to the PMHS deflection response at 3 m/s. These findings emphasize the need of 2D deflection measurement.

Biomechanical response of ribs under quasistatic frontal loading.

OBJECTIVE: The goal of the present study was to identify rib-level differences in fracture characteristics for individual ribs subjected to anterior-posterior loading. METHODS: Twenty-seven individual ribs were extracted from levels 2 to 10 from 3 postmortem human subjects (2 females and one male) and subjected to anterior-posterior loading at a quasistatic (2 mm/s) loading rate. The ribs were placed in a fixture that provided a pinned boundary condition at each extremity, and each specimen was loaded to failure. Reaction force and strains on the internal and external cortical surfaces of the ribs were measured. RESULTS: Rib 2 was found to be 3 to 4 times stiffer than rib 3, whereas all other ribs were comparable in stiffness to rib 3. Fracture forces, fracture displacement, and work to fracture showed no clear rib-level trends, although the young male subject consistently exhibited higher fracture force and work values than the elderly female subjects for a given rib level. The cortical strains on the external surface of the rib remained in tension during the loading, whereas the internal surface strains were in compression. The data from the present study were compared to a similar study performed at dynamic loading rates (1.43-1.85 m/s). The quasistatic tests exhibited lower peak force and greater normalized fracture displacement than the dynamic tests, though the work was comparable between the 2 studies. CONCLUSIONS: The present study is one of the few that focuses on testing the rib as an entire structure and can contribute to understanding of how the structural behavior of an individual rib contributes to the fracture tolerance of the overall thorax when undergoing frontal loading.

Morphology, distribution, mineral density and volume fraction of human calcified costal cartilage.

This study examines the properties of calcifying human costal cartilage and adjacent rib bone using qualitative and quantitative micro-computed tomography analysis. Calcifications are categorized with respect to location, microstructure, shape, and contiguity using a novel classification scheme and quantified in terms of mineral density, volume fraction, and length of infiltration from the costo-chondral junction (CCJ). Calcifications were present throughout the cartilage by location and ranged from small diffuse calcifications to nodes, rods, plates, and even large complex structures that exhibited a microstructural morphology similar to a cross-section of diaphysial bone, with a dense shell surrounding a trabecular core. Solid microstructure was most common for calcifications (44.5%), and the morphologies were found to vary with location, with rods and plates being most prevalent at the periphery (91.7% of all rods, 98.4% of all plates). The average mineral density of the calcifications over all locations and morphologies was 658.8±86.36, compared with 662.7±50.37 mgHA cm(-3) for the adjacent rib bone. The calcification volume fraction (6.54±4.71%) was less than the volume fraction of rib bone (21.62±6.44%). The length of contiguous calcification infiltrating from the CCJ into the costal cartilage, when present, was 19.21±11.65 mm. These changes in the costal cartilage should be considered in biomechanical models of the thorax since the presence, location, and morphology of the calcifications alter the material behavior of the costal cartilage, as well as the structural behavior of the entire rib.

Analysis of spinal motion and loads during frontal impacts. Comparison between PMHS and ATD.

Quantifying the kinematics of the human spine during a frontal impact is a challenge due to the multi-degree-of-freedom structure of the vertebral column. This papers reports on a series of six frontal impacts sled tests performed on three Post Mortem Human Surrogates (PMHS). Each subject was exposed first to a low-speed, non-injurious frontal impact (9 km/h) and then to a high-speed one (40 km/h). Five additional tests were performed using the Hybrid III 50(th) percentile male ATD for comparison with the PMHS. A 3D motion capture system was used to record the 6-degree-of-freedom motion of body segments (head, T1, T8, L2, L4 and pelvis). The 3D trajectories of individual bony structures in the PMHS were determined using bone-mounted marker arrays, thus avoiding skin-attached markers and their potential measurements artifacts. The PMHS spines showed different behavior between low and high speed. While at low speed the head and upper spinal segments lagged the lower portion of the spine and pelvis in reaching their maximum forward displacement (time for maximum forward head excursion was 254.3±31.9 ms and 140.3±9 ms for the pelvis), these differences were minimal at high speed (127±2.6 ms for the head vs. 116.7±3.5 ms for the pelvis). The ATD did not exhibit this speed-dependant behavior. Furthermore, the ATD's forward displacements were consistently less than those exhibited by the PMHS, regardless of the speed. Neck loads at the atlanto-occipital joint were estimated for the PMHS using inverse dynamics techniques and compared to those measured in the ATD. It was found that the axial and shear forces and the flexion moment at the upper neck of the PMHS were higher than those measured in the ATD.