Laboratory Reconstructions of Concussive Helmet-to-Helmet Impacts in the National Football League.

Seventeen concussive helmet-to-helmet impacts occurring in National Football League (NFL) games were analyzed using video footage and reconstructed by launching helmeted crash test dummies into each other in a laboratory. Helmet motion on-field and in the laboratory was tracked in 3D before, during, and after impact in multiple high frame rate video views. Multiple (3-10) tests were conducted for each of the 17 concussive cases (100 tests total) with slight variations in input conditions. Repeatability was assessed by duplicating one or two tests per case. The accuracy of the input conditions in each reconstruction was assessed based on how well the closing velocity, impact locations, and the path eccentricity of the dummy heads matched the video analysis. The accuracy of the reconstruction output was assessed based on how well the changes in helmet velocity (translational and rotational) from the impact matched the video analysis. The average absolute error in helmet velocity changes was 24% in the first test, 20% in the tests with the most accurate input configuration, and 14% in the tests with minimal error. Coefficients of variation in 22 repeated test conditions (1-2 per case) averaged 3% for closing velocity, 7% for helmet velocity changes, and 8% for peak head accelerations. Iterative testing was helpful in reducing error. A combination of sophisticated video analysis, articulated physical surrogates, and iterative testing was required to reduce the error to within half of the effect size of concussion.

Concussion with primary impact to the chest and the potential role of neck tension.

OBJECTIVES: Most biomechanical research on brain injury focuses on direct blows to the head. There are a few older studies that indicate craniocervical stretch could be a factor in concussion by causing strain in the upper spinal cord and brainstem. The objectives of this study are to assess the biomechanical response and estimate the strain in the upper cervical spine and brainstem from primary impact to the chest in American football. METHODS: Impact testing was conducted to the chest of a stationary unhelmeted and helmeted anthropomorphic test device (ATD) as well as the laboratory reconstruction of two NFL game collisions resulting in concussion. A finite element (FE) study was also conducted to estimate the elongation of the cervical spine under tensile and flexion loading conditions. RESULTS: The helmeted ATD had a 40% (t=9.84, p<0.001) increase in neck tensile force and an 8% (t=7.267, p<0.001) increase in neck flexion angle when compared with an unhelmeted ATD. The case studies indicated that the neck tension in the injured players exceeded tolerable levels from volunteer studies. The neck tension was combined with flexion of the head relative to the torso. The FE analysis, combined with a spinal cord coupling ratio, estimated that the strain along the axis of the upper cervical spinal cord and brainstem was 10%-20% for the combined flexion and tension loading in the two cases presented. CONCLUSION: Strain in the upper spinal cord and brainstem from neck tension is a factor in concussion.

Rethinking the foam cosmesis for people with lower limb absence.

BACKGROUND AND AIM: A recent survey of people with lower limb absence revealed that patients' satisfaction with their foam cosmesis is lower than desired. The aim of this project was to improve the lifelike appearance, functionality and durability of the cosmesis through a user-centred design methodology. TECHNIQUE: Concept development and prototyping led to a new cosmesis design which features a cut-out located at the knee, inserted with an artificial patella made of a more rigid foam. It also features a full-length zip which provides easy access for maintenance. The new cosmesis was then mechanically tested for over 1 million cycles and clinically tested by six transfemoral prosthesis users over 18 patient months. DISCUSSION: The new design is significantly more durable than the current standard model and has an enhanced lifelike appearance. It has potential to improve users' body image and reduce costs for healthcare providers. Clinical relevance This study contributes to practice by offering a new cosmesis design with enhanced appearance and durability, with the potential to improve patients' body image and reduce costs associated with cosmesis fitting and maintenance.

The Effects of Helmet Weight on Hybrid III Head and Neck Responses by Comparing Unhelmeted and Helmeted Impacts.

Most studies on football helmet performance focus on lowering head acceleration-related parameters to reduce concussions. This has resulted in an increase in helmet size and mass. The objective of this paper was to study the effect of helmet mass on head and upper neck responses. Two independent test series were conducted. In test series one, 90 pendulum impact tests were conducted with four different headform and helmet conditions: unhelmeted Hybrid III headform, Hybrid III headform with a football helmet shell, Hybrid III headform with helmet shell and facemask, and Hybrid III headform with the helmet and facemask with mass added to the shell (n = 90). The Hybrid III neck was used for all the conditions. For all the configurations combined, the shell only, shell and facemask, and weighted helmet conditions resulted in 36%, 43%, and 44% lower resultant head accelerations (p < 0.0001), respectively, when compared to the unhelmeted condition. Head delta-V reductions were 1.1%, 4.5%, and 4.4%, respectively. In contrast, the helmeted conditions resulted in 26%, 41%, and 49% higher resultant neck forces (p < 0.0001), respectively. The increased neck forces were dominated by neck tension. In test series two, testing was conducted with a pneumatic linear impactor (n = 178). Fourteen different helmet makes and models illustrate the same trend. The increased neck forces provide a possible explanation as to why there has not been a corresponding reduction in concussion rates despite improvements in helmets ability to reduce head accelerations.

On the accuracy of the Head Impact Telemetry (HIT) System used in football helmets.

On-field measurement of head impacts has relied on the Head Impact Telemetry (HIT) System, which uses helmet mounted accelerometers to determine linear and angular head accelerations. HIT is used in youth and collegiate football to assess the frequency and severity of helmet impacts. This paper evaluates the accuracy of HIT for individual head impacts. Most HIT validations used a medium helmet on a Hybrid III head. However, the appropriate helmet is large based on the Hybrid III head circumference (58 cm) and manufacturer's fitting instructions. An instrumented skull cap was used to measure the pressure between the head of football players (n=63) and their helmet. The average pressure with a large helmet on the Hybrid III was comparable to the average pressure from helmets used by players. A medium helmet on the Hybrid III produced average pressures greater than the 99th percentile volunteer pressure level. Linear impactor tests were conducted using a large and medium helmet on the Hybrid III. Testing was conducted by two independent laboratories. HIT data were compared to data from the Hybrid III equipped with a 3-2-2-2 accelerometer array. The absolute and root mean square error (RMSE) for HIT were computed for each impact (n=90). Fifty-five percent (n=49) had an absolute error greater than 15% while the RMSE was 59.1% for peak linear acceleration.