Objectives
To collect and analyse helmets from real-world equestrian accidents. To record reported head injuries associated with those accidents. To compare damage to helmets certified to different standards and the injuries associated with them.
Methods
Two hundred sixteen equestrian helmets were collected in total. One hundred seventy-six helmets from amateur jockeys were collected via accident helmet return schemes in the UK and USA, while 40 helmets from professional jockeys were collected by The Irish Turf Club. All helmet damage was measured, and associated head injury was recorded.
Results
Eighty-eight percent (189) of equestrian fall accidents returned an injury report of which 70% (139) reported a head injury. Fifty-four percent (75) of head injury cases had associated helmet damage while 46% had no helmet damage. Reported head injuries consisted of 91% (126) concussion, 4% (6) skull fractures, 1 (0.7%) subdural hematoma, 1 (0.7%) cerebral edema and 5 (3.6%) diffuse axonal injury (DAI). It is also shown that helmets certified to the most severe standard are overrepresented in this undamaged group (
p
<0.001).
Conclusions
It is clear that despite jockeys wearing a helmet, large proportions of concussion injuries still occur in the event of a jockey sustaining a fall. However, the data suggest it is likely that helmets reduce the severity of head injury as the occurrence of skull fracture is low. The proportion of undamaged helmets with an associated head injury suggests that many helmets may be too stiff relative to the surface they are impacting to reduce the risk of traumatic brain injury (TBI). It may be possible to improve helmet designs and certification tests to reduce the risk of head injury in low-severity impacts.
The aim of this study is to create a new database of human head physical properties based on a living adult population that can be used to inform the development of future biofidelic headforms. Relationships between head circumference and mass, as well as head moments of inertia and mass, are sufficiently linear to provide simple yet accurate values for the mass and inertia properties of differently sized heads. Physical data regarding the dimensions, mass, moments of inertia and centre of gravity location for the heads of 56 living adults were obtained using a non-invasive method based on computed tomography-based finite element models. The computed tomography data showed good agreement with published cadaver data and significantly less variation. The data set presented in this article provides an important basis for more biofidelic future headform designs. The linear equations associated with this new primary data set relate head circumference to head mass and moments of inertia: Head Mass = 0.18 × Head Circumference – 6.08, where mass is in kg and circumference is in cm, while Ixx = 79.88 × Head Mass – 132.88, Iyy = 81.70 × Head Mass – 128.38 and Izz = 53.88 × Head Mass – 86.66, where I is the moment of inertia in kg/cm2 and mass is in kg. The X, Y and Z axes correspond to forward, lateral and vertical directions and the XZ plane corresponds to the mid-sagittal plane. These results represent the first published human head physical property data that are based on a living population, rather than cadaver data. These data are freely available to all and should serve to improve the biofidelity of standard headforms in terms of their mass and moments of inertia.
The performance of equestrian helmets to protect against brain injuries caused by fall impacts against compliant surfaces such as turf has not been studied widely. We characterize the kinematic response of simulated fall impacts to turf through field tests on horse racetracks and laboratory experiments. The kinematic response characteristics and ground stiffness at different going ratings (GRs) (standard measurement of racetrack condition) were obtained from 1 m and 2 m drop tests of an instrumented hemispherical impactor onto a turf racetrack. The “Hard” rating resulted in higher peak linear accelerations and stiffness, and shorter impact durations than the “Soft” and “Heavy” ratings. Insignificant differences were found among the other GRs, but a strong overall relationship was evident between the “going rating” and the kinematic response. This relationship was used to propose a series of three synthetic foam anvils as turf surrogates in equestrian falls corresponding to ranges of GRs of (i) heavy-soft (H-S), (ii) good-firm (G-F), and (iii) firm-hard (F-H). Laboratory experiments consisted of a helmeted headform being dropped onto natural turf and the turf surrogate anvils using a monorail drop rig. These experiments revealed that the magnitudes and durations of the linear and rotational accelerations for helmeted impacts to turf/turf surrogates were similar to those in concussive sports falls and collisions. Since the compliance of an impacted surface influences the dynamic response of a jockey's head during a fall impact against the ground, it is important that this is considered during both accident reconstructions and helmet certification tests.
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