Conventional wisdom and the language in international helmet testing and certifi- cation standards suggest that appropriate helmet fit and retention during an impact are important factors in protecting the helmet wearer from impact-induced injury. This thesis aims to investigate impact-induced injury mechanisms in different helmet fit scenarios through analysis of simulated helmeted impacts with an anthropometric test device (ATD), an array of headform acceleration transducers and neck force/moment transducers, a dual high speed camera system, and helmet-fit force sensors developed in our research group based on Bragg gratings in optical fibre. To quantify fit and track dynamic helmet movement, novel methods were developed using fit force sensors and high speed cameras respectively. The development of these methods are described in this thesis. The application of these tools and existing practices are implemented in simulated helmet impacts.
To simulate impacts, an instrumented headform and flexible neck fall along a linear guide rail onto an anvil. An instrumented Hybrid III headform and neck is fit with a crash helmet and several fit scenarios can be simulated by making context specific adjustments to the helmet position index and/or helmet size. Specifically, 4 fit scenarios were studied: a normal, oversized, forward, and backward fit. Impact condition simulate a variety of scenarios, including a low (4 m/s) and high (6 m/s) impact velocity, a flat and angled anvil, as well as head and torso-first impacts. To quantify helmet retention, the movement of the helmet on the head is quantified using post-hoc image analysis. To quantify head and neck injury potential, biomechanical measures based on headform acceleration and neck force/moment are measured. These biomechanical measures, through comparison with established human tolerance curves, can estimate risk of severe life threatening and/or mild diffuse brain injury and osteoligamentous neck injury. Poor helmet fit did not significantly increase risk of skull fracture based on measured linear head acceleration. A backward fit was shown to increase the likelihood of brain injuries in certain torso-first impacts. Neck injury was found to be consistent between fit conditions in all tested impact scenarios. Helmet movement was found to be greatest in the backward fit scenario, with the greatest helmet displacements observed in torso first impacts indicating that in torso impacts more of the head could be exposed for subsequent impacts following a first impact.
In summary, helmets remained effective in mitigating risk of head and neck injury indicating that as long as the helmet is retained on the head during the first impact, it is an effective protection device. Poor fit did affect helmet retention, suggesting that poor fit in some cases could lead to head exposure and increased likelihood of injury in a second subsequent impact. The results in this thesis document trends in biomechanical measures from a laboratory study with several limitations. These results should not be construed to indicate deficiency in the design of the helmets used.
|1975||Padgaonkar AJ, Krieger KW, King AI. Measurement of angular acceleration of a rigid body using linear accelerometers. J Appl Mech. September 1975;42(3):552-556.|
|2003||Mertz HJ, Irwin AL, Prasad P. Biomechanical and scaling bases for frontal and side impact injury assessment reference values. Stapp Car Crash J. 2003;47:155-188. SAE 2003-22-0009.|
|1998||Kleinberger M, Sun E, Eppinger R, Kuppa S, Saul R. Development of Improved Injury Criteria for the Assessment of Advanced Automotive Restraint Systems. Washington, DC: National Highway Traffic Safety Administration (NHTSA); September 1998.|
|1966||Gurdjian ES, Roberts VL, Thomas LM. Tolerance curves of acceleration and intracrantal pressure and protective index in experimental head injury. J Trauma. September 1966;6(5):600-604.|
|1999||Eppinger R, Sun E, Bandak F, Haffner M, Khaewpong N, Maltese M, Kuppa S, Nguyen T, Takhounts E, Tannous R, Zhang A, Saul R. Development of Improved Injury Criteria for the Assessment of Advanced Automotive Restraint Systems - II. Washington, DC: National Highway Traffic Safety Administration (NHTSA); November 1999.|
|2015||Klug C, Feist F, Tomasch E. Testing of bicycle helmets for preadolescents. In: Proceedings of the 2015 International IRCOBI Conference on the Biomechanics of Injury. September 9-11, 2015; Lyon, France.136-155.|
|2013||Takhounts EG, Craig MJ, Moorhouse K, McFadden J, Hasija V. Development of brain injury criteria (BrIC). Stapp Car Crash J. November 2013;57:243-266.|
|1996||de Jager M, Sauren A, Thunnissen J, Wismans J. A global and a detailed mathematical model for head-neck dynamics. In: Proceedings of the 40th Stapp Car Crash Conference. November 4-6, 1996; Albuquerque, NM. Warrendale, PA: Society of Automotive Engineers:269-281. SAE 962430.|
|2003||Aare M, Halldin P. A new laboratory rig for evaluating helmets subject to oblique impacts. Traffic Inj Prev. September 2003;4(3):240-248.|
|2012||Dennison CR, Macri EM, Cripton PA. Mechanisms of cervical spine injury in rugby union: is it premature to abandon hyperflexion as the main mechanism underpinning injury? Br J Sports Med. 2012;46(8):545-.|
|1972||Gennarelli TA, Thibault LE, Ommaya AK. Pathophysiologic responses to rotational and translational accelerations of the head. In: Proceedings of the 16th Stapp Car Crash Conference. November 8-10, 1972; Detroit, MI. Warrendale, PA: Society of Automotive Engineers:296-308. SAE 720970.|
|2000||Newman JA, Shewchenko N, Welbourne E. A proposed new biomechanical head injury assessment function: the maximum power index. Stapp Car Crash J. 2000;44:215-247. SAE 2000-01-SC16.|
|2014||Cripton PA, Dressler DM, Stuart CA, Dennison CR, Richards D. Bicycle helmets are highly effective at preventing head injury during head impact: head-form accelerations and injury criteria for helmeted and unhelmeted impacts. Accid Anal Prev. September 2014;70:1-7.|
|2008||Takhounts EG, Ridella SA, Hasija V, Tannous RE, Campbell JQ, Malone D, Danelson K, Stitzel J, Rowson S, Duma S. Investigation of traumatic brain injuries using the next generation of Simulated Injury Monitor (SIMon) finite element head model. Stapp Car Crash J. 2008;52:1-31. SAE 2008-22-0001.|
|2005||Newman JA, Beusenberg MC, Shewchenko N, Withnall C, Fournier E. Verification of biomechanical methods employed in a comprehensive study of mild traumatic brain injury and the effectiveness of American football helmets. J Biomech. July 2005;38(7):1469-1481.|
|2006||Langlois JA, Rutland-Brown W, Wald MM. The epidemiology and impact of traumatic brain injury: a brief overview. J Head Trauma Rehabil. September–October 2006;21(5):375-378.|
|2003||Takhounts EG, Eppinger RH, Campbell JQ, Tannous RE, Power ED, Shook LS. On the development of the SIMon finite element head model. Stapp Car Crash J. 2003;47:107-133. SAE 2003-22-0007.|
|1986||Newman JA. A generalized acceleration model for brain injury threshold (GAMBIT). In: Proceedings of the 1986 International IRCOBI Conference on the Biomechanics of Impact. September 2-4, 1986; Zurich, Switzerland.121-131.|
|2009||Broglio SP, Sosnoff JJ, Shin S, He X, Alcaraz C, Zimmerman J. Head impacts during high school football: a biomechanical assessment. J Athl Train. August 2009;44(4):342-349.|
|1992||Margulies SS, Thibault LE. A proposed tolerance criterion for diffuse axonal injury in man. J Biomech. August 1992;25(8):917-923.|