Chris Sherwood

Prediction of Cervical Spine Injury Risk for the 6-Year-Old Child in Frontal Crashes

This article presents a series of 49 km/h sled tests using the Hybrid III 6-year-old dummy in a high-back booster, a low-back booster, and a three-point belt. Although a 10-year review at a level I trauma center showed that noncontact cervical spine injuries are rare in correctly restrained booster-age children, dummy neck loads exceeded published injury thresholds in all tests. The dummy underwent extreme neck flexion during the test, causing full-face contact with the dummys chest. These dummy kinematics were compared to the kinematics of a 12-year-old cadaver tested in a similar impact environment. The cadaver test showed neck flexion, but also significant thoracic spinal flexion which was nonexistent in the dummy. This comparison was expanded using MADYMO simulations in which the thoracic spinal stiffness of the dummy model was decreased to give a more biofidelic kinematic response. We conclude that the stiff thoracic spine of the dummy results in high neck forces and moments that are not representative of the true injury potential.

The Athletic Shoe in Football

Background: Foot and ankle injuries are common in sports, particularly in cleated athletes. Traditionally, the athletic shoe has not been regarded as a piece of protective equipment but rather as a part of the uniform, with a primary focus on performance and subjective feedback measures of comfort. Changes in turf and shoe design have poorly understood implications on the health and safety of players. Evidence Acquisition: A literature search of the MEDLINE and PubMed databases was conducted. Keywords included athletic shoewear, cleated shoe, football shoes, and shoewear, and search parameters were between the years 2000 and 2016. Study Design: Clinical review. Level of Evidence: Level 5. Results: The athletic shoe is an important piece of protective sports equipment. There are several important structural considerations of shoe design, including biomechanical compliance, cleat and turf interaction, and shoe sizing/fit, that affect the way an athlete engages with the playing surface and carry important potential implications regarding player safety if not understood and addressed. Conclusion: Athletic footwear should be considered an integral piece of protective equipment rather than simply an extension of the uniform apparel. More research is needed to define optimal shoe sizing, the effect that design has on mechanical load, and how cleat properties, including pattern and structure, interact with the variety of playing surfaces.

Implications of Functional Capacity Loss and Fatality for Vehicle Safety Prioritization

Objective: We investigate the use of the Functional Capacity Index (FCI) as a tool for establishing vehicle safety priorities by comparing the life year burden of injuries to the burden of fatality in frontal and side automotive crashes. We demonstrate FCI’s utility by investigating in detail the resulting disabling injuries and their life year costs. Methods: We selected occupants in the 2000–2013 NASS-CDS database involved in frontal and side crashes, merged their injuries with FCI, and then used the merged data to estimate each occupant’s overall functional loss. Lifetime functional loss was assessed by combining this measure of impairment with the occupants’ expected future life spans, estimated from the Social Security Administration’s Actuarial Life Table. Results: Frontal crashes produce a large number of disabling injuries, particularly to the lower extremities. In our population, these crashes are estimated to account for approximately 400,000 life years lost to disability in comparison with 500,000 life years lost to fatality. Victims of side crashes experienced a higher rate of fatality but a significantly lower rate of disabling injury (0.3 vs. 1.0%), resulting in approximately 370,000 life years lost to fatality versus 50,000 life years lost to disability. Conclusions: The burden of disabling injuries to car crash survivors should be considered when setting vehicle safety design priorities. In frontal crashes this burden in life years is similar to the burden attributable to fatality.

Forefoot bending stiffness of cleated American football shoes

In American football, hyper-dorsiflexion of the first metatarsophalangeal (1 MTP) joint is the predominant mechanism of 1 MTP sprains (turf toe). The risk of acute 1 MTP sprain has been found to increase as 1 MTP angle increases. The bending resistance of the shoe dictates the proportion of an externally applied load that can be passed into the shoe (i.e., not through the 1 MTP joint) and thus influences the magnitude of flexion imparted to the 1 MTP joint. This study quantified the forefoot bending resistance of a range of cleated American football shoes. A total of 21 pairs of size 12 shoes were dynamically tested over flexion angles from 30° to 90°. Bending stiffness ranged from 0.10 to 0.35 Nm/deg, while peak torque ranged from 5.1 to 16.6 Nm. The relationship between torque and flexion angle was nearly linear for all of the shoes tested and the peak torque values were substantially lower than 1 MTP joint moments that have been measured in the human foot during athletic activities. These results suggest that an opportunity exists to better balance athletic performance and acute 1 MTP joint injury risk by incorporating non-linearity into the torque-angle characteristic of football cleats, such that the proportion of external load borne by the shoe increases at flexion angles above 60°.

Quantifying the forefoot bending stiffness of cleated American football shoes using the Football American Shoe Tester (FAST)

In American football, hyper-dorsiflexion of the first metatarsophalangeal (first MTP) joint is the predominant mechanism of first MTP joint sprains (turf toe). The risk of acute first MTP joint sprain has been found to increase as first MTP joint angle increases. The bending resistance of the shoe dictates the proportion of an externally applied load that can be passed into the shoe (i.e. not through the first MTP joint) and thus may influence the magnitude of flexion imparted to the first MTP joint and hence the risk of injury. The current study introduces the Football American Shoe Tester (FAST), a flexion apparatus designed to measure the bending resistance of American football shoes at angles of forefoot dorsiflexion from 15° to 75°. The FAST was used to quantify the forefoot bending behaviour of a range of American football shoes. Thirty different models of US size 12 shoes were tested. Linearized bending stiffness ranged from 0.27 to 0.8 Nm/deg, while peak torque ranged from 11.8 to 25.5 N m. The testing revealed characteristic differences in torque-angle response across shoe models and quantified the extent of shoe stiffening at angles of dorsiflexion beyond those studied in the past.

Apparatus for measuring the forefoot bending stiffness of cleated American football shoes

Among the three GRF cushioning variables, maximum LR is recommended for evaluating heel cushioning performance, as suggested by its better agreement with mechanical impact scores. Tibial acceleration seems to be effective in differentiating shoe of varying mechanical heel impact scores during higher loading intensity. Further investigation on mechanical impact score with different loading intensities should be done to help footwear manufacturer in the design of cushioning evaluation protocol. Forefoot and rearfoot loading biomechanics should be better differentiated to explore the underlying shock attenuation mechanism of different shoe-subject interfaces and in different force intensities.

Validation of a videogrammetry technique for analysing American football helmet kinematics

ABSTRACT Professional American football games are recorded in digital video with multiple cameras, often at high resolution and high frame rates. The purpose of this study was to evaluate the accuracy of a videogrammetry technique to calculate translational and rotational helmet velocity before, during and after a helmet impact. In total, 10 football impacts were staged in a National Football League (NFL) stadium by propelling helmeted 50th percentile male crash test dummies into each other or the ground at speeds and orientations representative of concussive impacts for NFL players. The tests were recorded by experienced sports film crews to obtain video coverage and quality typically available for NFL games. A videogrammetry procedure was used to track the position and rotation of the helmet throughout the relevant time interval of the head impact. Compared with rigidly mounted retroreflective marker three dimensional (3-D) motion tracking that was concurrently collected in the experiments, videogrammetry accurately calculated changes in translational and rotational velocity of the helmet using high frame rate (two cameras at 240 Hz) video (7% and 15% error, respectively). Low frame rate (2 cameras at 60 Hz) video was adequate for calculating pre-impact translational velocity but not for calculating the translational or rotational velocity change of the helmet during impact.