Overturned abusive head trauma and shaken baby syndrome convictions in the United States: Prevalence, legal basis, and medical evidence.

BACKGROUND: Media reports and the Innocence Network assert that wrongful Abusive Head Trauma (AHT)/Shaken Baby Syndrome (SBS) convictions pervade the United States (U.S.) criminal justice system. Yet, no empirical evaluation of overturned AHT/SBS convictions has been conducted. OBJECTIVE: To evaluate the prevalence, legal basis, and characteristics of appellate rulings of AHT/SBS convictions. PARTICIPANTS AND SETTING: U.S. appellate cases in a legal database, Westlaw. METHODS: Retrospective review of AHT/SBS convictions that had appellate rulings from January 2008 through December 2018. Multiple search terms ensured all potential AHT/SBS cases were included. A mixed-methods analysis was conducted on overturned AHT/SBS convictions. RESULTS: We identified a total of 1431 unique AHT/SBS criminal convictions that had appellate rulings since 2008. Of those, 49 convictions (3%) were overturned, and 1382 (97%) were affirmed/upheld. Of those overturned, 20 cases (1% overall) were overturned on medical evidence-related grounds. The most common themes from the medical evidence-related reversals were controversy over the AHT/SBS diagnosis (n = 12) and accidental injury mechanism (n = 11). After being overturned on appeal, upon retrial, 42% of defendants either re-plead guilty to or were convicted again of the same offense. CONCLUSION(S): AHT/SBS convictions are rarely overturned on medical evidence-related grounds. When overturned, medical evidence-related themes seldom reflect new scientific or clinical discoveries, but rather are alternative or differing medical opinions from those offered at the original trial. Our data tends to support the concerns of other authors regarding irresponsible communication of medical information in AHT/SBS cases.

Aquatic treadmill water level influence on pelvic limb kinematics in cranial cruciate ligament-deficient dogs with surgically stabilised stifles.

OBJECTIVE: To compare pelvic limb joint kinematics and temporal gait characteristics during land-based and aquatic-based treadmill walking in dogs that have undergone surgical stabilisation for cranial cruciate ligament deficiency. MATERIALS AND METHODS: Client-owned dogs with surgically stabilised stifles following cranial cruciate ligament deficiency performed three walking trials consisting of three consecutive gait cycles on an aquatic treadmill under four water levels. Hip, stifle and hock range of motion; peak extension; and peak flexion were assessed for the affected limb at each water level. Gait cycle time and stance phase percentage were also determined. RESULTS: Ten client-owned dogs of varying breeds were evaluated at a mean of 55·2 days postoperatively. Aquatic treadmill water level influenced pelvic limb kinematics and temporal gait outcomes. Increased stifle joint flexion was observed as treadmill water level increased, peaking when the water level was at the hip. Similarly, hip flexion increased at the hip water level. Stifle range of motion was greatest at stifle and hip water levels. Stance phase percentage was significantly decreased when water level was at the hip. CLINICAL SIGNIFICANCE: Aquatic treadmill walking has become a common rehabilitation modality following surgical stabilisation of cranial cruciate ligament deficiency. However, evidence-based best practice guidelines to enhance stifle kinematics do not exist. Our findings suggest that rehabilitation utilising a water level at or above the stifle will achieve the best stifle kinematics following surgical stifle stabilisation.

Development and validation of a computer crash simulation model of an occupied adult manual wheelchair subjected to a frontal impact.

Wheelchairs are primarily designed for mobility and are not necessarily intended for use as motor vehicle seats. However, many wheelchairs serve as vehicle seats for individuals unable to transfer to a vehicle seat. Subjecting wheelchairs to sled testing, in part establishes the crashworthiness of wheelchairs used as motor vehicle seats. Computer simulations provide a supplemental approach for sled testing, to assess wheelchair response and loading under crash conditions. In this study a nonlinear, dynamic, computer model was developed and validated to simulate a wheelchair and occupant subjected to a frontal impact test (ANSI/RESNA WC19). This simulation model was developed utilizing data from two frontal impact 20 g/48 km/h sled tests, which consisted of identical, adult manual wheelchairs secured with 4-point tiedowns, occupied with a 50th percentile adult male anthropomorphic test device (ATD), restrained with a 3-point occupant restraint system. Additionally, the model was validated against sled data using visual comparisons of wheelchair and occupant kinematics, along with statistical assessments of outcome measures. All statistical evaluations were found to be within the acceptance criteria, indicating the model's high predictability of the sled tests. This model provides a useful tool for the development of crashworthy wheelchair design guidelines, as well as the development of transit-safe wheelchair technologies.

Evaluation of wheelchair sling seat and sling back crashworthiness.

Many wheelchairs are used as vehicle seats by those who cannot transfer to a vehicle seat. Although ANSI/RESNA WC-19 has been recently adopted as a standard to evaluate crashworthiness of the wheelchairs used as motor vehicle seats, replacement or after-market seats may not be tested to this standard. This study evaluated the crashworthiness of two specimens each of three unique sling backs and three unique sling seats using a static test procedure intended to simulate crash loading conditions. To pass the test, a sling back is required to withstand a 2290 lb load, and a sling seat should be capable of withstanding a 3750 lb load. All, but two sling back specimens which failed at 1567 lb and 1787 lb, withstood the test criterion load. Two of six tested sling seats failed to pass the test: one failed at 3123 lb and the other failed to sustain the load for 5 s although it reached the test criterion load. Most of the failures occurred at the seams of the side openings of upholsteries where the wheelchair frame inserts for attachment.

Computer simulation of stair falls to investigate scenarios in child abuse.

OBJECTIVES: To demonstrate the usefulness of computer simulation techniques in the investigation of pediatric stair falls. Since stair falls are a common falsely reported injury scenario in child abuse, our specific aim was to investigate the influence of stair characteristics on injury biomechanics of pediatric stair falls by using a computer simulation model. Our long-term goal is to use knowledge of biomechanics to aid in distinguishing between accidents and abuse. METHODS: A computer simulation model of a 3-year-old child falling down stairs was developed using commercially available simulation software. This model was used to investigate the influence that stair characteristics have on biomechanical measures associated with injury risk. Since femur fractures occur in unintentional and abuse scenarios, biomechanical measures were focused on the lower extremities. RESULTS: The number and slope of steps and stair surface friction and elasticity were found to affect biomechanical measures associated with injury risk. CONCLUSIONS: Computer simulation techniques are useful for investigating the biomechanics of stair falls. Using our simulation model, we determined that stair characteristics have an effect on potential for lower extremity injuries. Although absolute values of biomechanical measures should not be relied on in an unvalidated model such as this, relationships between accident-environment factors and biomechanical measures can be studied through simulation. Future efforts will focus on model validation.

Evaluation of wheelchair drop seat crashworthiness.

Wheelchair seating crash performance is critical to protecting wheelchair users who remain seated in their wheelchairs during transportation. Relying upon computer simulation and sled testing seat loads associated with a 20 g/48 kph (20 g/30 mph) frontal impact and 50th percentile male occupant were estimated to develop test criteria. Using a static test setup we evaluated the performance of various types of commercially available drop seats against the loading test criteria. Five different types of drop seats (two specimens each) constructed of various materials (i.e. plastics, plywood, metal) were evaluated. Two types of drop seats (three of the total 10 specimens) met the 16650 N (3750 lb) frontal impact test criteria. While additional validation of the test protocol is necessary, this study suggests that some drop seat designs may be incapable of withstanding crash level loads.

Evaluation of wheelchair seating system crashworthiness: "drop hook"-type seat attachment hardware.

OBJECTIVE: To evaluate the crashworthiness of commercially available hardware that attaches seat surfaces to the wheelchair frame. DESIGN: A low cost static crashworthiness test procedure that simulates a frontal impact motor vehicle crash. SETTING: Safety testing laboratory. SPECIMENS: Eleven unique sets of drop-hook hardware made of carbon steel (4), stainless steel (4), and aluminum (3). INTERVENTIONS: Replicated seat-loading conditions associated with a 20g/48 kph frontal impact. Test criterion for seat loading was 16,680 N (3750 lb). MAIN OUTCOME MEASURES: Failure load and deflection of seat surface. RESULTS: None of the hardware sets tested met the crashworthiness test criterion. All failed at less than 50% of the load that seating hardware could be exposed to in a 20g/48 kph frontal impact. The primary failure mode was excessive deformation, leading to an unstable seat support surface. CONCLUSIONS: Results suggest that commercially available seating drop hooks may be unable to withstand loading associated with a frontal crash and may not be the best option for use with transport wheelchairs.

Wheelchairs used as motor vehicle seats: seat loading in frontal impact sled testing.

Wheelchairs are not typically designed to function as motor vehicle seats. However, many wheelchair users are unable to transfer to a vehicle seat and instead travel seated in their wheelchair. ANSI/RESNA WC19: Wheelchairs Used as Seats in Motor Vehicles provides design and testing requirements, but does not provide wheelchair manufacturers with design guidance related to expected loads imposed upon wheelchair components during a crash. To provide manufacturers with crashworthy design guidance, our study measured wheelchair seat loading during 20g/48kph frontal impact sled tests with a 50th percentile male test dummy. Loading conditions were assessed using two different rear securement point positions. Results of four sled impact tests revealed downward loads ranging from 17 019 to 18 682 N, depending upon rear securement point configuration. Maximum fore/aft shear loads ranged from 4424 to 6717 N across the tests.

Wheelchair integrated occupant restraints: feasibility in frontal impact.

Individuals often use their wheelchair as a motor vehicle seat when traveling in motor vehicles. The current use of fixed vehicle-mounted wheelchair occupant restraint systems (FWORSs) often results in poor belt fit and discomfort. Additionally, satisfaction, usability and usage rate of FWORSs during transit use are often low. The automotive industry has shown improved occupant restraint usage, belt fit and injury protection when integrating the upper torso and pelvic restraint in a motor vehicle seat. This study compared occupant injury measures of a FWORS to a concept wheelchair integrated restraint system (WIRS) using a 20g frontal sled impact test with a 30 mph change in velocity. Neck loads, neck moments, head, pelvis and chest acceleration, sternum compression and knee and head excursion data were recorded from the wheelchair seated 50th percentile male hybrid III anthropomorphic test dummy (ATD). The WIRS resulted in a lower head injury criteria (HIC) value, lower sternum compression and a lower upper-torso restraint load than the FWORS. Compared with the FWORS, increased head, knee and wheelchair excursions and higher neck loads and moments were measured in the WIRS test. Both restraint scenario injury parameters were complied with occupant injury criteria based on General Motors Injury Assessment Reference Values (GM-IARVs) and occupant kinematic requirements defined by the Society of Automotive Engineers (SAE) voluntary standard, J2249. A higher motion criteria index was calculated for the WIRS scenario and a comparable combined injury criteria index was calculated for both restraint scenarios. The sled impact test showed WIRS concept feasibility, facilitating further development by industrial manufacturers who might further want to pursue this restraint principle to increase wheelchair occupant safety and comfort during transport in motor vehicles.

Development of a wheelchair occupant injury risk assessment method and its application in the investigation of wheelchair securement point influence on frontal crash safety.

To promote proper wheelchair securement in transportation, the proposed ANSI/RESNA Standard on Wheelchairs Used as Seats in Motor Vehicles will require that all transit wheelchairs be equipped with four securement points compatible with strap-type tiedowns. Through computer simulations, the location of these securement points has been found to influence wheelchair user response to a frontal crash. This study develops and employs an injury risk assessment method to compare the crashworthiness of various securement point configurations. The comparative injury risk assessment method is designed to predict the risk associated with internalized crash forces, as well as risk associated with secondary occupant impact with the vehicle interior. Injury criteria established by Federal Motor Vehicle Safety Standards and General Motors, along with excursion limitations set by the Society of Automotive Engineers (SAE) J2249 Wheelchair Tiedowns and Occupant Restraint Systems (WTORS) Standard were used as benchmarks for the risk assessment method. The simulation model subjected a secured commercial powerbase wheelchair with a seated 50th percentile male Hybrid III test dummy to a 20 g/30 mph crash. The occupant was restrained using pelvic and shoulder belts, and the wheelchair was secured with four strap-type tiedowns. Results indicated that securement points located 1.5 in to 2.5 in above the evaluated wheelchair's center of gravity provide the most effective occupant protection.

Proposed test method for and evaluation of wheelchair seating system (WCSS) crashworthiness.

Safety of motor vehicle seats is of great importance in providing crash protection to the occupant. An increasing number of wheelchair users use their wheelchairs as motor vehicle seats when traveling. A voluntary standard requires that compliant wheelchairs be dynamically sled impact tested. However, testing to evaluate the crashworthiness of add-on wheelchair seating systems (WCSS) independent of their wheelchair frame is not addressed by this standard. To address this need, this study developed a method to evaluate the crash-worthiness of WCSS with independent frames. Federal Motor Vehicle Safety Standards (FMVSS) 207 test protocols, used to test the strength of motor vehicle seats, were modified and used to test the strength of three WCSS. Forward and rearward loads were applied at the WCSS center of gravity (CGSS), and a moment was applied at the uppermost point of the seat back. Each of the three tested WCSS met the strength requirements of FMVSS 207. Wheelchair seat-back stiffness was also investigated and compared to motor vehicle seat-back stiffness.

Development of frontal impact crashworthy wheelchair seating design criteria using computer simulation.

When designing wheelchairs for use as motor vehicle seats, special design criteria must be followed to assure the crash safety of the wheelchair user. Failure of seating system components under crash loading conditions could lead to serious injury or fatality. In this study, seat and seat-back loading in a frontal crash are explored using computer simulation techniques. A previously validated simulation model consisting of a powerbase wheelchair and a seated 50th-percentile male test dummy subjected to a 20g/30mph frontal impact were used for the study. Since such a wide range of seating systems are available, parametric analyses were conducted to evaluate the influence of surface stiffness and seat-back angle on wheelchair seat and back loading. Seat loading varied with stiffness, ranging from 819-3,273 lb., while seat-back loading was found to be between 1,427-2,691 lb., depending upon back stiffness and recline angle.

Injury risk assessment of wheelchair occupant restraint systems in a frontal crash: a case for integrated restraints.

Obtaining proper occupant restraint fit when using a wheelchair as a motor vehicle seat is often difficult to attain with vehicle-mounted restraint systems. The comprehensive evaluation conducted in this study illustrates the occupant crash protection benefits of wheelchair-integrated restraint systems, as compared to vehicle-mounted restraint systems. Using computer crash simulation, occupant kinematic and biomechanical measures associated with a 20g/30mph frontal impact were evaluated and compared to injury criteria and SAE J2249 WTORS kinematic limits. These measures were also used to compile a Motion Criteria (MC) index and Combined Injury Criteria (CIC) index for each evaluated restraint scenario. These indices provide a composite method for comparing various crash scenarios. With the exception of an unsafe 36-inch height off-shoulder shoulder belt anchor scenario, the MC index was minimized for the integrated restraint scenario. Similarly, the CIC index was also minimized for the wheelchair-integrated restraint scenario. This preliminary study emphasizes the need for transfer of integrated restraint technology to the wheelchair transportation industry.

Evaluation of wheelchair back support crashworthiness: combination wheelchair back support surfaces and attachment hardware.

Automotive seats are tested for compliance with federal motor vehicle safety standards (FMVSS) to assure safety during impact. Many wheelchair users rely upon their wheelchairs to serve as vehicle seats. However, the crashworthiness of these wheelchairs during impact is often unknown. This study evaluated the crashworthiness of five combinations of wheelchair back support surfaces and attachment hardware using a static test procedure simulating crash loading conditions. The crashworthiness was tested by applying a simulated rearward load to each seat-back system. The magnitude of the applied load was established through computer simulation and biodynamic calculations. None of the five tested wheelchair back supports withstood the simulated crash loads. All failures were associated with attachment hardware.

Computer simulation and sled test validation of a powerbase wheelchair and occupant subjected to frontal crash conditions.

The Americans with Disabilities Act (ADA) has led to an increased number of wheelchair users seeking transportation services. Many of these individuals are unable to transfer to a vehicle and are instead required to travel seated in their wheelchairs. Unfortunately, wheelchairs are not typically designed with the same occupant protection features as motor vehicle seats, and wheelchair seated occupants may be at higher risk for injury in a crash. To study the effects of crash level forces on wheelchairs and their occupants, it is useful to simulate crash conditions using computer modeling. This study has used a dynamic lumped mass crash simulator, in combination with sled impact testing, to develop a model of a secured commercial powerbase and restrained occupant subjected to a 20 g/30 mph frontal motor vehicle crash. Time histories profiles of simulation-generated wheelchair kinematics, occupant accelerations, tiedown forces and occupant restraint forces were compared to sled impact testing for model validation. Validation efforts for this model were compared to validation results found acceptable for the ISO/SAE surrogate wheelchair model. This wheelchair-occupant simulation model can be used to investigate wheelchair crash response or to evaluate the influence of various factors on occupant crash safety.

Testing and evaluation of wheelchair caster assemblies subjected to dynamic crash loading.

Wheelchair designs based upon loads applied quasi-statically during normal mobility use are apt to be inadequate to handle the increased level of dynamic crash forces that may be encountered when using the wheelchair as a motor vehicle seat. The purpose of this study was to characterize the integrity of wheelchair caster assemblies under simulated crash conditions. This study utilized dynamic drop (DD) testing, with loading levels and rates adjusted to match those found previously in sled impact testing and computer crash simulations. The results verify that current caster assembly designs may not be able to withstand forces associated with a crash. Five of seven evaluated caster assemblies failed when loaded to 8,007 N, or less, at loading rates seen in sled testing. DD testing used in this study is a valuable tool that can be used in the design of transport wheelchair components.

Wheeled mobility device database for transportation safety research and standards.

To address the issue of safely accessing and securing wheeled mobility devices in motor vehicles, more information characterizing current-production devices was needed. In a recent effort, frame characteristics of wheeled mobility devices were defined and a database developed for recording characteristics relevant to access and securement. A representative number of devices have been surveyed to measure key characteristics, and these measures have been recorded in the database. This paper details the development of the database and frame characterization scheme, the methods used to survey currently available wheeled mobility devices, and some descriptive statistics resulting from an analysis of the data. A discussion of how this information is being used in research aimed at developing technology and safety standards to ensure vehicle access and safe transportation, as well as other potential uses, is also included.

Development of transportable wheelchair design criteria using computer crash simulation.

The Americans with Disabilities Act (ADA) has led to an increase in disabled travelers, many of whom are unable to transfer to a vehicle seat and are required to use their wheelchair to fulfill this function. ANSI/RESNA is currently developing a transportable wheelchair standard which will identify design requirements and testing methods for wheelchairs suitable for transport. Wheelchair manufacturers should begin to modify their existing design criteria established for a normal mobility function to design criteria appropriate for a transportation function which may subject the wheelchair to large dynamic crash forces. A thorough understanding of the crash environment and its effect on the wheelchair is necessary to insure the safety of the wheelchair user. To assist manufacturers in the design effort, this study uses mathematical crash simulations to evaluate loads imposed upon a wheelchair when subjected to a 48 kph/20 g frontal crash. Using a four-point belt tiedown system to secure the wheelchair, securement point, seat, lap belt anchor, and wheel loads are evaluated under three different securement configurations. Results show that positioning of rear securement points near the wheelchair center of gravity can serve as an effective strategy for managing crash response and loadings on the wheelchair. Force ranges for each of the evaluated parameters, derived for a 50th percentile male using a simulated power wheelchair, are provided for use as a preliminary guide when designing transportable wheelchairs.

Shoulder belt anchor location influences on wheelchair occupant crash protection.

An investigation of the effect of the shoulder belt's upper anchor point location on crash protection during wheelchair transportation was conducted using a lumped parameter crash victim simulator. While varying the upper anchor point location in each of three directions, the occupant kinematics and injury criteria of the Hybrid III test dummy were determined. Through comparison of these parameters and their associated trends, it was determined that varying the location of the anchor point has a significant effect on the crash protection of the occupant.