Introduction: In American football, cranial impacts can occur at centric or non-centric locations leading to differing linear and rotational kinematics of the head and brain. Finite element modeling(FEM) allows for studying the effects of these varying forces on the brain and testing the ability of novel helmet technology to reduce the severity of brain injury in a computational model.
Methods: Performance tests were conducted on top performing football helmets, including the most common football helmets worn in the NFL: Riddell Speed, Riddell Speedflex, Schutt Air XP Pro, Xenith Epic+, and Vicis ZERO1. Helmets were tested using a pneumatic linear impactor at a single velocity commonly causing injury in the NFL(5.5m/s). A Hybrid III headform and neck on a linear bearing table were impacted in the approximate center of mass(CoM) and then 2.5cm for 5 consecutive non-centric locations. The kinematics of the head following impact was then input into the Simulated Injury Monitor FEM (SIMon). The cumulative strain damage measure - 15 and 25(CSDM15,CSDM25), correlates for diffuse axonal injury, were subsequently calculated and plotted onto previously defined abbreviated injury scale(AIS) curves to obtain a risk of varying degrees of head injury in a computational model.
Results: CSDM15 showed significantly lower values for impacts at or near the CoM, while highly non-centric impacts were associated with the most simulated brain damage. Non-centric impacts also showed the largest difference in CSDM values between all helmets(-12.5cm (p<00001),-10cm(p<0.0001), CoM(p<0.0001),+10cm(p<0.0001),+12.5cm(p<0.0001)). There was a significant difference in the risk of AIS 2 injury, i.e concussion, between all tested helmets, with a greater difference seen at impacts further from the CoM(-12.5cm(p<0.0001),-10cm(p<0.0001),CoM (p<0.0001),+10cm(p=0.0002),+12.5cm(p<0.0001)).
Conclusions: Non-centric cranial impacts lead to higher rates of injury in a simulated brain model. As such, novel football helmet design and standards should incorporate testing of centric and non-centric impacts to decrease the risk of brain injury.
Patient Care: Our research allows for a better understanding of impacts that cause concussion. This information can be used to improve helmet design to minimize the risk of concussion in athletics.
Learning Objectives: -- To understand the utility of finite element modeling for advancing helmet technology
-- To understand the types of cranial impacts leading to concussion and other forms of intracranial trauma