Rear-facing versus forward-facing child restraints: an updated assessment.

OBJECTIVES: The National Highway Traffic Safety Administration and the American Academy of Pediatrics recommend children be placed in rear-facing child restraint systems (RFCRS) until at least age 2. These recommendations are based on laboratory biomechanical tests and field data analyses. Due to concerns raised by an independent researcher, we re-evaluated the field evidence in favour of RFCRS using the National Automotive Sampling System Crashworthiness Data System (NASS-CDS) database. METHODS: Children aged 0 or 1 year old (0-23 months) riding in either rear-facing or forward-facing child restraint systems (FFCRS) were selected from the NASS-CDS database, and injury rates were compared by seat orientation using survey-weighted χ2 tests. In order to compare with previous work, we analysed NASS-CDS years 1988-2003, and then updated the analyses to include all available data using NASS-CDS years 1988-2015. RESULTS: Years 1988-2015 of NASS-CDS contained 1107 children aged 0 or 1 year old meeting inclusion criteria, with 47 of these children sustaining injuries with Injury Severity Score of at least 9. Both 0-year-old and 1-year-old children in RFCRS had lower rates of injury than children in FFCRS, but the available sample size was too small for reasonable statistical power or to allow meaningful regression controlling for covariates. CONCLUSIONS: Non-US field data and laboratory tests support the recommendation that children be kept in RFCRS for as long as possible, but the US NASS-CDS field data are too limited to serve as a strong statistical basis for these recommendations.

Thoracic spine morphology of a pseudo-biped animal model (kangaroo) and comparisons with human and quadruped animals.

PURPOSE: Based on the structural anatomy, loading condition and range of motion (ROM), no quadruped animal has been shown to accurately mimic the structure and biomechanical function of the human spine. The objective of this study is to quantify the thoracic vertebrae geometry of the kangaroo, and compare with adult human, pig, sheep, and deer. METHODS: The thoracic vertebrae (T1-T12) from whole body CT scans of ten juvenile kangaroos (ages 11-14 months) were digitally reconstructed and geometric dimensions of the vertebral bodies, endplates, pedicles, spinal canal, processes, facets and intervertebral discs were recorded. Similar data available in the literature on the adult human, pig, sheep, and deer were compared to the kangaroo. A non-parametric trend analysis was performed. RESULTS: Thoracic vertebral dimensions of the juvenile kangaroo were found to be generally smaller than those of the adult human and quadruped animals. The most significant (p < 0.001) correlations (Rho) found between the human and kangaroo were in vertebrae and endplate dimensions (0.951 ≤ Rho ≤ 0.963), pedicles (0.851 ≤ Rho ≤ 0.951), and inter-facet heights (0.891 ≤ Rho ≤ 0.967). The deer displayed the least similar trends across vertebral levels. CONCLUSIONS: Similarities in thoracic spine vertebral geometry, particularly of the vertebrae, pedicles and facets may render the kangaroo a more clinically relevant human surrogate for testing spinal implants. The pseudo-biped kangaroo may also be a more suitable model for the human thoracic spine for simulating spine deformities, based on previously published similarities in biomechanical loading, posture and ROM.

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.

Etiology and biomechanics of first metatarsophalangeal joint sprains (turf toe) in athletes.

Sprains of the first metatarsophalangeal (MTP) joint, referred to colloquially as "turf toe," are a debilitating sports injury because the hallux is pivotal to an athletes' ability to accelerate and cut. Severe sprains may require weeks to full recovery, and injuries requiring surgery may prevent an athlete from full athletic participation for months. Whereas the diagnosis and treatment of turf toe are well documented in the literature, less is known about the biomechanics of this joint and the mechanical properties of the structures that compose it. Nevertheless, this information is vital to those, such as equipment designers, who attempt to develop athletic footwear and surfaces intended to reduce the likelihood of injury. To that end, this review summarizes the literature on the anatomy of the first MTP joint, on biomechanical studies of the first MTP joint, and on the incidence, mechanisms, and treatment of turf toe. Furthermore, gaps in the literature are identified and opportunities for future research are discussed. Only through a thorough synthesis of the anatomic, biomechanical, and clinical knowledge regarding first MTP joint sprains can appropriate countermeasures be designed to reduce the prevalence and severity of these injuries.

The contribution of the perichondrium to the structural mechanical behavior of the costal-cartilage.

The costal-cartilage in the human ribcage is a composite structure consisting of a cartilage substance surrounded by a fibrous, tendon-like perichondrium. Current computational models of the human ribcage represent the costal-cartilage as a homogeneous material, with no consideration for the mechanical contributions of the perichondrium. This study sought to investigate the role of the perichondrium in the structural mechanical behavior of the costal-cartilage. Twenty-two specimens of postmortem human costal-cartilage were subjected to cantilevered-like loading both with the perichondrium intact and with the perichondrium removed. The test method was chosen to approximate the cartilage loading that occurs when a concentrated, posteriorly directed load is applied to the midsternum. The removal of the perichondrium resulted in a statistically significant (two-tailed Student's t-test, p< or =0.05) decrease of approximately 47% (95% C.I. of 35-58%) in the peak anterior-posterior reaction forces generated during the tests. When tested with the perichondrium removed, the specimens also exhibited failure in the cartilage substance in the regions that experienced tension from bending. These results suggest that the perichondrium does contribute significantly to the stiffness and strength of the costal-cartilage structure under this type loading, and should be accounted for in computational models of the thorax and ribcage.

Position-Specific Circumstances of Concussions in the NFL: Toward the Development of Position-Specific Helmets.

Consideration of position-specific features of the NFL concussion environment could enable improved risk mitigation through the design of position-specific helmets to improve self-protection as well as protection for the other player with whom the contact occurs. The purpose of this paper is to quantify position-specific features of scenarios resulting in concussions to NFL players, and the players they contact, by reviewing all game footage (broadcast and non-broadcast) over 4 seasons. Position-specific features were documented for 647 concussions in which a primary exposure could be visualized, including impact source, helmet impact location, activity, and the other player with whom the contact occurred. Findings include the over-representation of helmet-to-ground impacts to the rear of the quarterback's helmet, the high frequency of impacts to the side (upper) location of both concussed players and the players they contacted regardless of position, and distinct differences in the circumstances of concussions to cornerbacks and safeties. The study shows that some features of concussion scenarios are common to all positions, but several position-specific features exist and can inform the design of position-specific helmets for NFL players.

Incidence of Lower Extremity Injury in the National Football League: 2015 to 2018.

BACKGROUND: Lower extremity injuries are the most common injuries in professional sports and carry a high burden to players and teams in the National Football League (NFL). Injury prevention strategies can be refined by a foundational understanding of the occurrence and effect of these injuries on NFL players. PURPOSE: To determine the incidence of specific lower extremity injuries sustained by NFL players across 4 NFL seasons. STUDY DESIGN: Descriptive epidemiology study. METHODS: This retrospective, observational study included all time-loss lower extremity injuries that occurred during football-related activities during the 2015 through 2018 seasons. Injury data were collected prospectively through a leaguewide electronic health record (EHR) system and linked with NFL game statistics and player participation to calculate injury incidence per season and per 10,000 player-plays for lower extremity injuries overall and for specific injuries. Days lost due to injury were estimated through 2018 for injuries occurring in the 2015 to 2017 seasons. RESULTS: An average of 2006 time-loss lower extremity injuries were reported each season over this 4-year study, representing a 1-season risk of 41% for an NFL player. Incidence was stable from 2015 to 2018, with an estimated total missed time burden each NFL season of approximately 56,700 player-days lost. Most (58.7%) of these injuries occurred during games, with an overall higher rate of injuries observed in preseason compared with regular season (11.5 vs 9.4 injuries per 10,000 player-plays in games). The knee was the most commonly injured lower extremity region (29.3% of lower body injuries), followed by the ankle (22.4%), thigh (17.2%), and foot (9.1%). Hamstring strains were the most common lower extremity injury, followed by lateral ankle sprains, adductor strains, high ankle sprains, and medial collateral ligament tears. CONCLUSION: Lower extremity injuries affect a high number of NFL players, and the incidence did not decrease over the 4 seasons studied. Prevention and rehabilitation protocols for these injuries should continue to be prioritized.

Synthetic Turf: History, Design, Maintenance, and Athlete Safety.

CONTEXT:: Synthetic turf has become an increasingly common playing surface for athletics and has changed dramatically since its introduction more than 50 years ago. Along with changes to surface design, maintenance needs and recommendations have become more standardized and attentive both to upkeep and player-level factors. In particular, synthetic turf maintenance as it relates to athlete health and safety is an important consideration at all levels of play. EVIDENCE ACQUISITION:: A literature search of MEDLINE and PubMed for publications between the years 1990 and 2018 was conducted. Keywords included s ynthetic turf, artificial turf, field turf, and playing surface. Additionally, expert opinion through systematic interviews and practical implementation were obtained on synthetic turf design and maintenance practices in the National Football League. STUDY DESIGN:: Clinical review. LEVEL OF EVIDENCE:: Level 5. RESULTS:: Synthetic turf has changed considerably since its inception. Playing surface is a critical component of the athletic environment, playing a role both in performance and in athlete safety. There are several important structural considerations of third-generation synthetic turf systems currently used in the United States that rely heavily on strong and consistent maintenance. A common misconception is that synthetic turf is maintenance free; in fact, however, these surfaces require routine maintenance. Whether athletes experience more injuries on synthetic over natural surfaces is also of interest among various levels and types of sport. CONCLUSION:: Modern synthetic turf is far different than when originally introduced. It requires routine maintenance, even at the level of local athletics. It is important for sports medicine personnel to be familiar with playing surface issues as they are often treating athletes at the time of injury and should maintain a level of awareness of contemporary research and practices regarding the relationships between synthetic turf and injury.

Higher Rates of Lower Extremity Injury on Synthetic Turf Compared With Natural Turf Among National Football League Athletes: Epidemiologic Confirmation of a Biomechanical Hypothesis.

BACKGROUND: Biomechanical studies have shown that synthetic turf surfaces do not release cleats as readily as natural turf, and it has been hypothesized that concomitant increased loading on the foot contributes to the incidence of lower body injuries. This study evaluates this hypothesis from an epidemiologic perspective, examining whether the lower extremity injury rate in National Football League (NFL) games is greater on contemporary synthetic turfs as compared with natural surfaces. HYPOTHESIS: Incidence of lower body injury is higher on synthetic turf than on natural turf among elite NFL athletes playing on modern-generation surfaces. STUDY DESIGN: Cohort study; Level of evidence, 3. METHODS: Lower extremity injuries reported during 2012-2016 regular season games were included, with all 32 NFL teams reporting injuries under mandated, consistent data collection guidelines. Poisson models were used to construct crude and adjusted incidence rate ratios (IRRs) to estimate the influence of surface type on lower body injury groupings (all lower extremity, knee, ankle/foot) for any injury reported as causing a player to miss football participation as well as injuries resulting in ≥8 days missed. A secondary analysis was performed on noncontact/surface contact injuries. RESULTS: Play on synthetic turf resulted in a 16% increase in lower extremity injuries per play than that on natural turf (IRR, 1.16; 95% CI, 1.10-1.23). This association between synthetic turf and injury remained when injuries were restricted to those that resulted in ≥8 days missed, as well as when categorizations were narrowed to focus on distal injuries anatomically closer to the playing surface (knee, ankle/foot). The higher rate of injury on synthetic turf was notably stronger when injuries were restricted to noncontact/surface contact injuries (IRRs, 1.20-2.03; all statistically significant). CONCLUSION: These results support the biomechanical mechanism hypothesized and add confidence to the conclusion that synthetic turf surfaces have a causal impact on lower extremity injury.

Indentation stiffness of aging human costal cartilage.

Costal cartilage, connecting the ribs and sternum, serves a mechanical function in the body. It undergoes structural changes with aging but it is unclear if its material properties are affected by these changes. To investigate this question, experimental indentation load-relaxation tests were performed on human costal cartilage as a function of specimen age and sex. The experimental data were fit to spherical indentation ramp-relaxation solutions generated previously by elastic-viscoelastic correspondence [Mattice JM, Lau AG, Oyen ML and Kent RW. Spherical indentation load-relaxation of soft biological tissues. J Mater Res 2006;8:2003-10]. Numerical values of short- and long-time shear modulus and of material time-constants were examined as a function of age. Costal cartilage calcification was assessed with blinded scoring of computed tomography reconstructions of the ribcage and mechanical properties were correlated with calcification score. Overall, the costal cartilage midsubstance was slightly stiffer than articular cartilage, and did not show significant variation in stiffness with age or specimen calcification. Increased age did result in increased local variability of the indentation stiffness results. Future studies will be required to address the findings of the current study that although calcification did increase with age, the calcification was primarily found on the costal cartilage periphery, thus insignificantly affecting the midsubstance stiffness.

Propagation of Syndesmotic Injuries During Forced External Rotation in Flexed Cadaveric Ankles.

BACKGROUND: Forced external rotation of the foot is a mechanism of ankle injuries. Clinical observations include combinations of ligament and osseous injuries, with unclear links between causation and injury patterns. By observing the propagation sequence of ankle injuries during controlled experiments, insight necessary to understand risk factors and potential mitigation measures may be gained. HYPOTHESIS: Ankle flexion will alter the propagation sequence of ankle injuries during forced external rotation of the foot. STUDY DESIGN: Controlled laboratory study. METHODS: Matched-pair lower limbs from 9 male cadaveric specimens (mean age, 47.0 ± 11.3 years; mean height, 178.1 ± 5.9 cm; mean weight, 94.4 ± 30.9 kg) were disarticulated at the knee. Specimens were mounted in a test device with the proximal tibia fixed, the fibula unconstrained, and foot translation permitted. After adjusting the initial ankle position (neutral, n = 9; dorsiflexed, n = 4; plantar flexed, n = 4) and applying a compressive preload to the tibia, external rotation was applied by rotating the tibia internally while either lubricated anteromedial and posterolateral plates or calcaneal fixation constrained foot rotation. The timing of osteoligamentous injuries was determined from acoustic sensors, strain gauges, force/moment readings, and 3-dimensional bony kinematics. Posttest necropsies were performed to document injury patterns. RESULTS: A syndesmotic injury was observed in 5 of 9 (56%) specimens tested in a neutral initial posture, in 100% of the dorsiflexed specimens, and in none of the plantar flexed specimens. Superficial deltoid injuries were observed in all test modes. CONCLUSION: Plantar flexion decreased and dorsiflexion increased the incidence of syndesmotic injuries compared with neutral matched-pair ankles. Injury propagation was not identical in all ankles that sustained a syndesmotic injury, but a characteristic sequence initiated with injuries to the medial ligaments, particularly the superficial deltoid, followed by the propagation of injuries to either the syndesmotic or lateral ligaments (depending on ankle flexion), and finally to the interosseous membrane or the fibula. CLINICAL RELEVANCE: Superficial deltoid injuries may occur in any case of hyper-external rotation of the foot. A syndesmotic ankle injury is often concomitant with a superficial deltoid injury; however, based on the research detailed herein, a deep deltoid injury is then concomitant with a syndesmotic injury or offloads the syndesmosis altogether. A syndesmotic ankle injury more often occurs when external rotation is applied to a neutral or dorsiflexed ankle. Plantar flexion may shift the injury to other ankle ligaments, specifically lateral ligaments.

Video Analysis of Reported Concussion Events in the National Football League During the 2015-2016 and 2016-2017 Seasons.

BACKGROUND: Concussions in American football remain a high priority of sports injury prevention programs. Detailed video review provides important information on causation, the outcomes of rule changes, and guidance on future injury prevention strategies. PURPOSE: Documentation of concussions sustained in National Football League games played during the 2015-2016 and 2016-2017 seasons, including consideration of video views unavailable to the public. STUDY DESIGN: Descriptive epidemiology study. METHODS: All reported concussions were reviewed with all available video footage. Standardized terminology and associated definitions were developed to describe and categorize the details of each concussion. RESULTS: Cornerbacks sustained the most concussions, followed by wide receivers, then linebackers and offensive linemen. Half (50%) of concussions occurred during a passing play, 28% during a rushing play, and 21% on a punt or kickoff. Tackling was found to be the most common activity of concussed players, with the side of the helmet the most common helmet impact location. The distribution of helmet impact source-the object that contacted the concussed player's helmet-differed from studies of earlier seasons, with a higher proportion of helmet-to-body impacts (particularly shoulder) and helmet-to-ground impacts and with a lower proportion of helmet-to-helmet impacts. Helmet-to-ground concussive impacts were notable for the high prevalence of impacts to the back of the helmet and their frequency during passing plays. CONCLUSION: Concussion causation scenarios in the National Football League have changed over time. CLINICAL RELEVANCE: The results of this study suggest the need for expanded evaluation of concussion countermeasures beyond solely helmet-to-helmet test systems, including consideration of impacts with the ground and with the body of the opposing player. It also suggests the possibility of position-specific countermeasures as part of an ongoing effort to improve safety.

Mechanisms of abdominal organ injury in seat belt-restrained children.

BACKGROUND: Previous research has identified key predictors of elevated abdominal injury risk in seat belt-restrained child vehicle occupants; however these data cannot be used to isolate specific mechanisms or sources of injury to suggest strategies for prevention. METHODS: Using a large child-focused crash surveillance system, cases of seat belt-restrained children who sustained an internal abdominal injury in a frontal crash were studied using standard crash investigation protocols. A second group of cases of restrained children in similar crashes without abdominal injury was investigated. Medical, crash, and child characteristics of each case were analyzed in the context of known biomechanics of abdominal injury to determine the mechanisms of injury and associated kinematics. RESULTS: Review of 21 cases of abdominal injury identified belt loading directly over the injured organ as the most common mechanism of injury. Three unique kinematic patterns were identified that varied by the initial position of the lap belt and kinematics of the upper torso. Sixty percent of the drivers and 90% of the other child occupants in these crashes sustained either no or minor injury. In the 16 no abdominal injury cases, all but one sustained external bruising to their abdomen and contact injury to the head and face. CONCLUSIONS: This evaluation of crashes in which belted children did and did not sustain abdominal injuries revealed key characteristics about their mechanism. In this data set, belt compression directly on the abdomen, manifested by improper initial placement of the seat belt, poor child posture, or misuse of the shoulder belt, resulted in abdominal injury in low-severity crashes in which other occupants sustained little injury. The cases pointed to control of torso excursion by consistent use of the shoulder belt and suggested that technologies such as lap belt pretensioners or belt-positioning booster seats might be a possible strategy, among others, for prevention.

Fiber-based modeling of in situ ankle ligaments with consideration of progressive failure.

Ligament sprains account for a majority of injuries to the foot and ankle complex among athletic populations. The infeasibility of measuring the in situ response and load paths of individual ligaments has precluded a complete characterization of their mechanical behavior via experiment. In the present study a fiber-based modeling approach of in situ ankle ligaments was developed and validated for determining the heterogeneous force-elongation characteristics and the consequent injury patterns. Nine major ankle ligaments were modeled as bundles of discrete elements, corresponding functionally to the structure of collagen fibers. To incorporate the progressive nature of ligamentous injury, the limit strain at the occurrence of fiber failure was described by a distribution function ranging from 12% to 18% along the width of the insertion site. The model was validated by comparing the structural kinetic and kinematic response obtained experimentally and computationally under well-controlled foot rotations. The simulation results replicated the 6 degree-of-freedom bony motion and ligamentous injuries and, by implication, the in situ deformations of the ligaments. Gross stiffness of the whole ligament derived from the fibers was comparable to existing experimental data. The present modeling approach provides a biomechanically realistic, interpretable and computationally efficient way to characterize the in situ ligament slack, sequential and heterogeneous uncrimping of collagen fascicles and failure propagation as the external load is applied. Applications of this model include functional ankle joint mechanics, injury prevention and countermeasure design for athletes.

Searching for the "sweet spot": the foot rotation and parallel engagement of ankle ligaments in maximizing injury tolerance.

Ligament sprains, defined as tearing of bands of fibrous tissues within ligaments, account for a majority of injuries to the foot and ankle complex in field-based sports. External rotation of the foot is considered the primary injury mechanism of syndesmotic ankle sprains with concomitant flexion and inversion/eversion associated with particular patterns of ligament trauma. However, the influence of the magnitude and direction of loading vectors to the ankle on the in situ stress state of the ligaments has not been quantified in the literature. The objective of the present study was to search for the maximum injury tolerance of a human foot with an acceptable subfailure distribution of individual ligaments. We used a previously developed and comprehensively validated foot and ankle model to reproduce a range of combined foot rotation experienced during high-risk sports activities. Biomechanical computational investigation was performed on initial foot rotation from [Formula: see text] of plantar flexion to [Formula: see text] of dorsiflexion, and from [Formula: see text] of inversion to [Formula: see text] of eversion prior to external rotation. Change in initial foot rotation shifted injury initiation among different ligaments and resulted in a wide range of injury tolerances at the structural level (e.g., 36-125 Nm of rotational moment). The observed trend was in agreement with a parallel experimental study that initial plantar flexion decreased the incidence of syndesmotic injury compared to a neutral foot. A mechanism of distributing even loads across ligaments subjected to combined foot rotations was identified. This mechanism is potential to obtain the maximum load-bearing capability of a foot and ankle while minimizing the injury severity of ligaments. Such improved understanding of ligament injuries in athletes is necessary to facilitate injury management by clinicians and countermeasure development by biomechanists.

Transient and long-time kinetic responses of the cadaveric leg during internal and external foot rotation.

The purpose of this study was to determine the long-time and transient characteristics of the moment generated by external (ER) and internal (IR) rotation of the calcaneus with respect to the tibia. Two human cadaver legs were disarticulated at the knee joint while maintaining the connective tissue between the tibia and fibula. An axial rotation of 21° was applied to the proximal tibia to generate either ER or IR while the fibula was unconstrained and the calcaneus was permitted to translate in the transverse plane. These boundary conditions were intended to allow natural motion of the fibula and for the effective applied axis of rotation to move relative to the ankle and subtalar joints based on natural articular motions among the tibia, fibula, talus, and calcaneus. A load cell at the proximal tibia measured all components of force and moment. A quasi-linear model of the moment along the tibia axis was developed to determine the transient and long-time loads generated by this ER/IR. Initially neutral, everted, inverted, dorsiflexed, and plantarflexed foot orientations were tested. For the neutral position, the transient elastic moment was 16.5N-m for one specimen and 30.3N-m for the other in ER with 26.3 and 32.1N-m in IR. The long-time moments were 5.5 and 13.2N-m (ER) and 9.0 and 9.5N-m (IR). These loads were found to be transient over time similar to previous studies on other biological structures where the moment relaxed as time progressed after the initial ramp in rotation.

Determination of the in situ mechanical behavior of ankle ligaments.

The mechanical behavior of ankle ligaments at the structural level can be characterized by force-displacement curves in the physiologic phase up to the initiation of failure. However, these properties are difficult to characterize in vitro due to the experimental difficulties in replicating the complex geometry and non-uniformity of the loading state in situ. This study used a finite element parametric modeling approach to determine the in situ mechanical behavior of ankle ligaments at neutral foot position for a mid-sized adult foot from experimental derived bony kinematics. Nine major ankle ligaments were represented as a group of fibers, with the force-elongation behavior of each fiber element characterized by a zero-force region and a region of constant stiffness. The zero-force region, representing the initial tension or slackness of the whole ligament and the progressive fiber uncrimping, was identified against a series of quasi-static experiments of single foot motion using simultaneous optimization. A range of 0.33-3.84mm of the zero-force region was obtained, accounting for a relative length of 6.7±3.9%. The posterior ligaments generally exhibit high-stiffness in the loading region. Following this, the ankle model implemented with in situ ligament behavior was evaluated in response to multiple loading conditions and proved capable of predicting the bony kinematics accurately in comparison to the cadaveric response. Overall, the parametric ligament modeling demonstrated the feasibility of linking the gross structural behavior and the underlying bone and ligament mechanics that generate them. Determination of the in situ mechanical properties of ankle ligaments provides a better understanding of the nonlinear nature of the ankle joint. Applications of this knowledge include functional ankle joint mechanics and injury biomechanics.

Estimation of conditions evoking fracture in finger bones under pinch loading based on finite element analysis.

A finger finite element (FE) model was created from CT images of a Japanese male in order to obtain a shape-biofidelic model. Material properties and articulation characteristics of the model were taken from the literature. To predict bone fracture and realistically represent the fracture pattern under various loading conditions, the ESI-Wilkins-Kamoulakos rupture model in PAM-CRASH (ESI Group S.A., Paris, France) was utilized in this study with parameter values of the rupture model determined by compression testing and simulation of porcine fibula. A finger pinch simulation was then conducted to validate the finger FE model. The force-displacement curve and fracture load from the pinch simulation was compared to the result of finger pinch test using cadavers. Simulation results are coincident with the test result, indicating that the finger FE model can be used in an analysis of finger bone fracture during pinch accident. With this model, several pinch simulations were conducted with different pinching object's stiffness and pinching energy. Conditions for evoking finger bone fracture under pinch loading were then estimated based on these results. This study offers a novel method to predict possible hazards of manufactured goods during the design process, thus finger injury due to pinch loading can be avoided.

Scaling approach in predicting the seatbelt loading and kinematics of vulnerable occupants: How far can we go?

OBJECTIVE: Occupants with extreme body size and shape, such as the small female or the obese, were reported to sustain high risk of injury in motor vehicle crashes (MVCs). Dimensional scaling approaches are widely used in injury biomechanics research based on the assumption of geometrical similarity. However, its application scope has not been quantified ever since. The objective of this study is to demonstrate the valid range of scaling approaches in predicting the impact response of the occupants with focus on the vulnerable populations. METHODS: The present analysis was based on a data set consisting of 60 previously reported frontal crash tests in the same sled buck representing a typical mid-size passenger car. The tests included two categories of human surrogates: 9 postmortem human surrogates (PMHS) of different anthropometries (stature range: 147-189 cm; weight range: 27-151 kg) and 5 anthropomorphic test devices (ATDs). The impact response was considered including the restraint loads and the kinematics of multiple body segments. For each category of the human surrogates, a mid-size occupant was selected as a baseline and the impact response was scaled specifically to another subject based on either the body mass (body shape) or stature (the overall body size). To identify the valid range of the scaling approach, the scaled response was compared to the experimental results using assessment scores on the peak value, peak timing (the time when the peak value occurred), and the overall curve shape ranging from 0 (extremely poor) to 1 (perfect match). Scores of 0.7 to 0.8 and 0.8 to 1.0 indicate fair and acceptable prediction. RESULTS: For both ATDs and PMHS, the scaling factor derived from body mass proved an overall good predictor of the peak timing for the shoulder belt (0.868, 0.829) and the lap belt (0.858, 0.774) and for the peak value of the lap belt force (0.796, 0.869). Scaled kinematics based on body stature provided fair or acceptable prediction on the overall head/shoulder kinematics (0.741, 0.822 for the head; 0.817, 0.728 for the shoulder) regardless of the anthropometry. The scaling approach exhibited poor prediction capability on the curve shape for the restraint force (0.494 and 0.546 for the shoulder belt; 0.585 and 0.530 for the lap belt). It also cannot well predict the excursion of the pelvis and the knee. CONCLUSIONS: The results revealed that for the peak lap belt force and the forward motion of the head and shoulder, the underlying linear relationship with body size and shape is valid over a wide anthropometric range. The chaotic nature of the dynamic response cannot be fully recovered by the assumption of the whole-body geometrical similarity, especially for the curve shape. The valid range of the scaling approach established in this study can be reasonably referenced in predicting the impact response of a given specific population with expected deviation. Application of this knowledge also includes proposing strategies for restraint configuration and providing reference for ATD and/or human body model (HBM) development for vulnerable occupants.

Experimental investigation of the effect of occupant characteristics on contemporary seat belt payout behavior in frontal impacts.

OBJECTIVE: The goal of this study was to investigate the influence of the occupant characteristics on seat belt force vs. payout behavior based on experiment data from different configurations in frontal impacts. METHODS: The data set reviewed consists of 58 frontal sled tests using several anthropomorphic test devices (ATDs) and postmortem human subjects (PMHS), restrained by different belt systems (standard belt, SB; force-limiting belt, FLB) at 2 impact severities (48 and 29 km/h). The seat belt behavior was characterized in terms of the shoulder belt force vs. belt payout behavior. A univariate linear regression was used to assess the factor significance of the occupant body mass or stature on the peak tension force and gross belt payout. RESULTS: With the SB, the seat belt behavior obtained by the ATDs exhibited similar force slopes regardless of the occupant size and impact severities, whereas those obtained by the PMHS were varied. Under the 48 km/h impact, the peak tension force and gross belt payout obtained by ATDs was highly correlated to the occupant stature (P =.03, P =.02) and body mass (P =.05, P =.04), though no statistical difference with the stature or body mass were noticed for the PMHS (peak force: P =.09, P =.42; gross payout: P =.40, P =.48). With the FLB under the 48 km/h impact, highly linear relationships were noticed between the occupant body mass and the peak tension force (R(2) = 0.9782) and between the gross payout and stature (R(2) = 0.9232) regardless of the occupant types. CONCLUSIONS: The analysis indicated that the PMHS characteristics showed a significant influence on the belt response, whereas the belt response obtained with the ATDs was more reproducible. The potential cause included the occupant anthropometry, body mass distribution, and relative motion among body segments specific to the population variance. This study provided a primary data source to understand the biomechanical interaction of the occupant with the restraint system. Further research is necessary to consider these effects in the computational studies and optimized design of the restraint system in a more realistic manner.