Chapter 5 - Concussive and subconcussive brain trauma: the complexity of impact biomechanics and injury risk in contact sport

Abstract

Head impacts that transfer mechanical energy to the skull and create brain injuries have unique dynamic responses and brain tissue trauma characteristics. The magnitude of the impact energy and how it is transmitted creates three-dimensional linear and rotational accelerations of the head, resulting in unique strains on brain tissue. Biomechanical investigations of head injuries in contact sports have historically focused on attenuating energy transfer to the skull and brain. Typically, severe life-threatening events are caused by high-energy impact events that result in anatomic damage. Protective equipment attenuates energy transmission to neural tissues to decrease the risk of structural damage. In addition to reducing risk of skull fracture, helmets work by increasing impact compliance, to decrease the magnitude of the head's dynamic response and increase the duration of the event. This strategy helps prevent severe traumatic brain injuries and shifts the risk to concussion and repetitive head impact exposure. Metabolic, cellular, and physiologic responses characterize cumulative brain trauma that may manifest years later. Relying on the presence of symptoms to establish injury is subjective and limited in capturing the risks associated with neural tissue trauma. To more effectively capture brain injury risks in contact sports, we present the concept of brain trauma profiling, involving impact magnitude, frequency, interval, and duration of exposure. Brain trauma profiling captures and describes the cumulative and acute trauma-associated injury risks unique to each sport, level of play, and player position.