J Neurosurg 116:222–233, 2012 222 J Neurosurg / Volume 116 / January 2012 A vAilAble data and statistics regarding concussion and Tbi vary widely. Nevertheless, it has been estimated that approximately 300,000 sports-re- lated concussions 53 and upwards of 3.8 million sport- and recreation-related Tbis 28 occur annually in the US, with direct medical and indirect costs in the tens of billions yearly. 16 American football is the leading cause of sports- related concussion in the US. 19 And the concussion crisis is underestimated, as evidenced by the fact that approxi- mately 53% of American football–related concussions in high school go unreported. 30 The term “concussion” has been used to describe a gamut of injuries and disorders resulting from the tradi- tional acute symptomatic concussion from a single head impact, including rare cases of transient loss of conscious- ness (reported in < 1 in 10 concussed athletes 23,48 ) and more frequent neurological dysfunctions such as headache, diz- ziness, confusion, disorientation, blurred vision, balance deicits, delayed reaction time, amnesia, sleep disturbanc- es, neck pain, and fatigue. 31 Further, clinically silent sub- concussive injuries from accumulated head impact doses over months, years, or decades can be present. both types of injuries can cause reversible as well as irreversible brain damage. Although concussion has been widely described as a type of Tbi, mild Tbi, concussive Tbi, mild head in- jury, closed head injury, minor head trauma, subconcussive impact test comparisons of 20th and 21st century American football helmets laboratory investigation AdAm BArtsch, Ph.d., 1,2 EdwArd BENzEl, m.d., 1–3 ViNcENt miElE, m.d., 2–4 ANd VikAs PrAkAsh, Ph.d. 2,5 1 Spine Research Laboratory; 3 Department of Neurosurgery, Neurological Institute, Cleveland Clinic; 2 Cleveland Traumatic Neuromechanics Consortium; 5 Department of Mechanical Engineering, Case Western Reserve University, Cleveland, Ohio; and 4 United Hospital Center Neuro-Spine Center, Bridgeport, West Virginia Object. Concussion is the signature American football injury of the 21st century. Modern varsity helmets, as compared with vintage leather helmets, or “leatherheads,” are widely believed to universally improve protection by reducing head impact doses and head injury risk for the 3 million young football players in the US. The object of this study was to compare the head impact doses and injury risks with 11 widely used 21st century varsity helmets and 2 early 20th century leatherheads and to hypothesize what the results might mean for children wearing similar varsity helmets. Methods. in an injury biomechanics laboratory, the authors conducted front, oblique front, lateral, oblique rear, and rear head impact tests at 5.0 m/second using helmeted headforms, inducing near- and subconcussive head impact doses on par with approximately the 95th percentile of on-ield collision severity. They also calculated impact dose injury risk parameters common to laboratory and on-ield traumatic neuromechanics: linear acceleration, angular acceleration, angular velocity, Gadd Severity index, diffuse axonal injury, acute subdural hematoma, and brain con- tusion. Results. in many instances the head impact doses and head injury risks while wearing vintage leatherheads were comparable to or better than those while wearing several widely used 21st century varsity helmets. Conclusions. The authors do not advocate reverting to leather headgear, but they do strongly recommend, espe- cially for young players, instituting helmet safety designs and testing standards, which encourage the minimization of linear and angular impact doses and injury risks in near- and subconcussive head impacts. (DOI: 10.3171/2011.9.JNS111059) kEy words • concussion • American football • football helmet • high school football • youth football • traumatic brain injury Abbreviations used in this paper: AiS = Abbreviated injury Scale; CSDM05 = cumulative strain damage measure; DAi = diffuse axo- nal injury; DDM = dilatational damage measure; GSi = Gadd Sever- ity index; NFl = National Football league; NOCSAe = National Operating Committee on Standards for Athletic equipment; RMDM = relative motion damage measure; SiMon = Simulated injury Monitor; Tbi = traumatic brain injury.