medRxiv preprint doi: https://doi.org/10.1101/2020.05.05.20092569; this version posted May 12, 2020. The copyright holder for this preprint (which was not certified by peer review) is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. It is made available under a CC-BY-ND 4.0 International license . Effectiveness of 2nd Skull Products in Reducing Head Impact in Simulated Sports 1 5 1,2,3,4 Marina Ritchie , Honghuang Lin , Rhoda Au 1 Department of Anatomy & Neurobiology, Boston University School of Medicine, Boston, MA 02118, USA 2 Department of Neurology, Boston University School of Medicine, Boston, MA 02118, USA 3 Framingham Heart Study, National Heart, Lung, and Blood Institute, Boston, MA 01702, USA 4 Department of Epidemiology, Boston University School of Public Health, Boston, MA 02118, USA 5 Section of Computational Biomedicine, Department of Medicine, Boston University School of Medicine, Boston, MA 02118, USA * Correspondence: Marina Ritchie [email protected] Keywords: head impact, traumatic brain injuries, contact sports, protective headgears, concussion Abstract Cumulative effects of repetitive head impact have been highly associated with short and long term neurological conditions. Despite high rates of head injuries, many people in the U.S. and around the world continue to participate in collision sports. As one approach to address this concern, 2nd Skull has developed supplemental protective headgears including a skull cap, scrum cap and headband that can be utilized in both helmet and non-helmet sports. To test the effectiveness of 2nd Skull products as an adjunctive tool to reduce the severity of head impact, data were extracted from a series of tests completed at four sites under laboratory conditions using linear, projectile and rotational impactor to simulate blows to the head in sports. The majority of test cases showed the same pattern of reduced impact severity with the addition of 2nd Skull padding. It remains to be seen if these laboratory results will translate to the field. Introduction In the past five years, there has been a surge of interest in literature and media surrounding sports- related injuries and their long-term consequences. More specifically, contact sports have been a topic of considerable discussion due to the pace of neuropathological studies evidencing chronic traumatic encephalopathy (CTE) in subsets of populations with high exposure to collision and impact (Bieniek et al., 2020; Mckee et al., 2009; Mez et al., 2020). While popularity and participation have not deflated, the increased risk of traumatic brain injuries (TBI) associated with sports raises the issue of whether this is a public health concern. The most common form of TBI as a recognized medical condition is a concussion, which is currently defined by evidence of a blow to the head that results in symptoms most often lasting from a few hours to a few weeks but can persist for months or even years (Shaw et al., 2002). Consequences of concussions are of great concern in sports-related contexts, with 1.6 to 3.8 million athletes in the US experiencing sports-related concussions each year, contributing to large healthcare expenditures (Langlois et al., 2006; Marshall, 2012). There is wide variability in acute symptoms of mild TBI (mTBI) ranging from headaches, dizziness, blurred or doubled vision, and memory loss (Prince & Bruhns, 2017). While most symptoms dissipate quickly, they may develop into chronic conditions and cause neurodegeneration (Cruz-Haces et al., 2017; Mez et al., 2017). Longitudinal studies have suggested that history of TBI can have pathological long-term effects such as an increased risk of Alzheimer’s disease (AD) and CTE (Fleminger et al., 2003; Gavett et al., 2011). Even without the loss of consciousness, repetitive head impacts (RHI) and sub- NOTE: This preprint reports new research that has not been certified by peer review and should not be used to guide clinical practice. medRxiv preprint doi: https://doi.org/10.1101/2020.05.05.20092569; this version posted May 12, 2020. The copyright holder for this preprint (which was not certified by peer review) is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. EffectivenessIt is madeof 2 ndavailable Skull under Products a CC-BY-ND in Reducing4.0 International Head license Impact . in Simulated Sports concussive blows have acute and chronic consequences including structural and functional changes to the brain (Mainwaring et al., 2018; Davenport et al., 2016). Conditions due to repetitive head trauma were first noticed in former boxers in the1920s and was commonly referred to as “punch-drunk syndrome” (Martland, 1928). Now punch-drunk syndrome is commonly associated with CTE or other TBIs. CTE is a neurodegenerative disease associated with exposure to repetitive head impacts (RHI), like those incurred during American football. In a study conducted by Mez and colleagues, the brains of 202 deceased American football players were studied for neuropathological evidence of CTE (Mez et al., 2017). Evidence of CTE was found in 87% of the brains, suggesting that long-term neurological conditions may be related to sports-related head impact. Furthermore, 47% of the studied brains indicated severe neurodegenerative pathology that resulted in dementia-related or Parkinsonian-related death amongst these individuals (Mez et al., 2017). Along with AD and CTE, these injuries can result in behavioral changes, post-concussive syndrome, and motor neuron diseases which are disproportionate to typical age-related changes (Babcock et al., 2013; Cole et al., 2015; Robbins et al., 2014). Despite the accumulating recognition of associations between repetitive head injuries and neurological disorders, little is known about effective treatment approaches, which highlight the importance of risk reduction and potential prevention (Mez et al., 2017; Maas et al., 2017). Preventative headgears made to reduce head injury risk have been tested and implemented on a large scale in professional and semi-professional sports including the National Football League. Special attention has been paid to helmets, with numerous prototypes undergoing rigorous testing to determine models that optimally reduce head impact severity (Bartsch et al., 2012; Bottlang et al., 2020; Viano et al., 2006). While other types of protective headgear have also been evaluated, the scientific consistency and validity have predominantly been reported from those that are helmet based (Sone et al., 2017). Cutting edge helmets, however, are professional or semi-elite focused with limited data on adjunctive products and are not readily available at the general population level. To address this issue, 2nd Skull Inc. has developed novel caps which incorporate a thin layer of impact management material into a traditional under-helmet liner cap. While many athletes choose to wear thin liner caps underneath these helmets for reasons such as sun protection and sweat management, 2nd Skull’s scientifically engineered 2mm Skull Cap with linear, projectile and rotational protection can add a layer of supplementary insulation to the helmets without changing the existing safety protocol. Furthermore, 2nd Skull has also developed headbands and scrum caps for non-helmet sports making it scalable to a broader population. To investigate the effectiveness of 2nd Skull products as an adjunctive buffer against impact, test series at independent third-party laboratories were conducted. Results obtained from the trials were consolidated and quantitatively reviewed to further evaluate the efficacy and overall pattern across all sites. The objective of this study is to examine the effect of 2nd Skull products on the protection against impacts. The results from multiple independent laboratories were evaluated and compared. Method 2nd Skull products In contact sports, the addition of helmets has generally been associated with larger reduction in response metrics of impact that reach the head. However, protective headgear often pose a series of trade-offs between safety, comfort and other sport-specific parameters (Graham et al., 2014). The adaptable characteristics of 2nd Skull products, however, are engineered to improve energy management of impact for use with a variety of helmet designs (i.e. single hit versus multiple-impact 2 medRxiv preprint doi: https://doi.org/10.1101/2020.05.05.20092569; this version posted May 12, 2020. The copyright holder for this preprint (which was not certified by peer review) is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. EffectivenessIt is madeof 2 ndavailable Skull under Products a CC-BY-ND in Reducing4.0 International Head license Impact . in Simulated Sports helmets) as well as absorb impact for non-helmet sports. Both the cap and headband have a thin layer of lightweight poron XRD made from urethane molecules that are soft and flexible at rest but harden under sudden pressure (2nd Skull, n.d). This mechanism has been developed for protection against linear impact from direct hits. Whereas previous reports have focused on linear impact in contact sports, recent studies experimentally investigating the effect of rotational impact have proposed rotational kinematics to be a better indicator of TBI risk (Kleiven, 2013). In response to current data, 2nd Skull products have added an independent layer between the head and helmet, which creates a slip pane upon rotation impact. It has been hypothesized that this structure will reduce the amount of energy transferred to the head. The lightness of the cap also protects the head from rotational acceleration. While thicker and heavier layers can protect the head from linear acceleration, added mass and radius to the head can result in increased rotational acceleration (Graham et al., 2014). Experimental tests To test the efficacy of risk reduction, independent third-party laboratories were commissioned by 2nd Skull to complete a series of tests that adhered to the National Operating Committee on Standards for Athletic Equipment (NOCSAE) and American Society for Testing and Materials (ASTM) standards for new helmets.