Subdural hematoma Dr. John Lloyd has served attorneys nationwide for 25+ years in biomechanics, human factors, helmet testing and motorcycle accident expert
Dr. John Lloyd recently conducted a biomechanical study to evaluate motorcycle helmets in terms of their ability to provide protection against traumatic head and brain injuries. Motorcycle helmet testing proves inadequate protection against concussion and diffuse traumatic brain injuries associated.
Motorcycle accident victims account for more than 340,000 fatalities annually, with the United States ranking 8th highest worldwide in the number of motorcycle accident deaths. 75% of all fatal motorcycle accidents involve brain injury, with rotational forces acting on the brain the primary cause of mortality. Current motorcycle helmets are effective at reducing head injuries associated with blunt impact. However, the mechanism of diffuse traumatic brain injury is biomechanically very different.
Samples of 9 motorcycle helmet models, representing full-face, three-quarter and shorty designs were evaluated. Helmets, fitted to an instrumented Hybrid III head and neck, were dropped at 13 mph in accordance with DOT motorcycle helmet testing standards.
Results show that, on average, there is a 67% risk of concussion and a 10% probability of severe or fatal brain injury associated with a relatively minor 13mph helmeted head impact.
In conclusion, motorcycle helmets provide inadequate protection against concussion and diffuse traumatic brain injuries associated with even relatively moderate impact.
To consider whether a motorcycle helmet might reduce the risk of brain trauma in a motorcycle accident it is first important to understand the two primary mechanisms associated with traumatic brain injury – impact loading and impulse loading, according to motorcycle helmet expert, Dr. John Lloyd.
Impact loading involves a direct blow transmitted primarily through the center of mass of the head, resulting in extracranial focal injuries, such as contusions, lacerations and external hematomas, as well as skull fractures. Shock waves from blunt force trauma may also cause underlying focal brain injuries, such as cerebral contusions, subarachnoid hematomas and intracerebral hemorrhages.
Whereas, impulse or inertial loading caused by sudden movement of the brain relative to the skull, produces cerebral concussion. Inertial loading at the surface of the brain can cause subdural hemorrhage due to bridging vein rupture, whereas if affecting the neural structures deeper within the brain can produce diffuse axonal injury (DAI).
Epidemiology Studies
Two major epidemiologic studies into the causation of motorcycle accidents have been conducted in North America and Europe: the Hurt Report and the MAIDS report. The Hurt Report showed that failure of motorists to detect and recognize motorcycles in traffic is the predominating cause of motorcycle accidents. Seventy-five percent of accidents were found to involve a motorcycle and a passenger vehicle, while the remaining 25% of accidents were single motorcycle accidents. Two-thirds of motorcycle-car crashes occurred when the car driver failed to see the approaching motorcycle and violated the rider’s right-of-way. Findings indicate that severity of injury increases with speed, alcohol motorcycle size and speed.
The MAIDS study (Motorcycle Accidents In Depth Study) is the most recent epidemiologic study of accidents involving motorcycles, scooters and mopeds, which was conducted in 1999 to investigate motorcycle accident exposure data across five European countries. Key findings show that passenger cars were the most frequent collision partner (60%), where 69% of the drivers report that they did not see the motorcycle and the predominance of motorcycle accidents (54.3%) occurred at an intersection.
In 1995, the European Commission Directorate General for Energy and Transport initiated a Cooperative Scientific and Technical Research (COST) program to investigate Motorcycle Safety Helmets. Several agencies from Finland, the United Kingdom, France and Germany participated in this study, which compiled and analyzed data from 4,700 motorcycle fatalities in Europe, each year. The COST report documents that 75% of all fatal motorcycle accidents involve head injury. Linear forces were present in only 31% of fatal head injuries, while rotational forces were found to be the primary cause in over 60% of cases. Within the scope of this study experiments were performed using drop tests with accelerometers to measure linear and rotational accelerations of the brain and skull mass associated with different types of impacts. These tests confirmed rotational acceleration to be a primary cause of brain injury in helmeted motorcycle accidents.
While the motorcycle helmet is currently the most effective means of protection for riders, data suggests that motorcycle helmets are only 37-42% effective in preventing fatal injury. By reducing the effects of blunt trauma to the head it is generally believed that risk of brain injury, including concussion, axonal injury and hematoma would also be reduced. However, the mechanisms of head and brain injury are very different. New research shows that these mechanisms are poorly coupled, contrary to previous beliefs.
Summary
Motorcycle helmet expert report that rotational forces acting on the brain are the underlying cause of traumatic brain injuries.
Motorcycle helmets, including those certified under DOT and SNELL standards are designed to mitigate forces associated with linear acceleration.
According to motorcycle helmet expert, helmets are not currently certified under either DOT or SNELL standard against their ability to protect against the angular / rotational forces.
Epidemiologic evidence from the COST-327 report indicates that motorcycle helmets do not provide adequate protection against closed head and brain injuries
New Research
Motorcycle helmet expert Dr. John Lloyd recently published a new study: Biomechanics of Motorcycle Helmets: Protection Against Head and Brain Injury. Testing proves that motorcycle helmets provide inadequate protection against concussion and severe traumatic brain injury associated with even relatively minor head impact
The common belief among riders is that a motorcycle helmet protects the whole head, including the brain. However testing standards in Europe (ECE 22.05) and the US (DOT & Snell), which involve dropping helmeted headforms from heights of 2-3 meters onto a steel plate, only evaluate a motorcycle helmet in terms of its ability to protect against blunt force trauma, such as skull fractures and penetrating head injuries. The mechanism underlying diffuse brain injuries, such as concussions and brain hemorrhages is distinctly different, but is not assessed by current motorcycle helmet testing standards.
Imagine a bowl of jelly, where the bowl represents the skull and the jelly represents the brain. The bowl (skull) serves to protect the jelly (brain) from impact by dispersing forces over a larger surface area. If the bowl were impacted such that the force passes through the center of the jelly, the jelly moves very little. This is called linear force. Whereas, if you rotate the bowl of jelly between your hands you will see that the jelly moves quite a lot, especially towards its center. This is called a rotational force.
In reality, most motorcycle helmet impacts will produce both linear and rotational forces. In the case of head and brain injury, linear forces are responsible for injuries such as bruises and fractures. Whereas rotational forces cause the nerves and blood vessels in the brain to stretch and tear, leading to concussions, injury to the nerve fibers (axonal trauma) and brain bleeding (hematomas).
The human head is designed to protect the brain against typical impacts associated with daily living, such as normal bumps and falls. The skull can be thought of as a helmet to the brain by resisting penetrating injury to the brain. While the scalp glides over the skull to decrease rotational forces, thereby reducing the risk and severity of diffuse brain injuries. However, the forces associated with motorcycle collisions far exceed that which the human skull and scalp was intended to protect. Hence in motorcycling the use of a helmet to reduce the risk of such injuries is typically mandated.
Helmets are designed with 3 principal components – the outer shell, the inner liner and a comfort layer. The shell is typically made of polycarbonate plastics or fiberglass and serves two purposes; to minimize the likelihood that a sharp object might penetrate the head, and to dissipate the impact over a larger surface area. The inner liner is made from EPS foam (polystyrene) and serves to absorb the impact forces. The comfort layer does nothing more than provide comfort between the head and the polystyrene liner. Unfortunately, the polystyrene liner has limited effectiveness at reducing the rotational forces – those responsible for diffuse brain injuries – below safe levels.
A cooperative study was undertaken in Europe in the late 1990s to examine motorcycle accidents and their causes. Based on data from 4,700 helmeted motorcyclist deaths, the study found head injuries accounted for three-quarters of all fatalities. More than 60 percent of which were brain injuries caused by rotational forces, while only 30 percent of fatal head injuries were due to linear forces. This extensive study proves that motorcycle helmets are inadequate in providing necessary protection against diffuse brain injuries.
One might propose that protection against diffuse brain injury ought to deserve a higher priority. After all, the skull will likely heal from trauma, but the brain may not.
The challenge with protective headgear, including motorcycle, military and sports helmets is that, due to the characteristics of the liner materials, the head is directly coupled to the helmet. That is, the head and helmet are effectively joined and move as one. Therefore upon impact, any rotational forces generated on the helmet are transmitted directly to the brain. In fact, due to the size of helmets rotational forces can actually be amplified. The solution lies in de-coupling the head from the helmet, much the way that the scalp is de-coupled from the skull, so that the helmet can have some degree of rotation independent of the head. In this way, the rotational forces are dampened before they are transmitted to the brain, thereby lessening the risk and severity of brain injury.
BRAINS, Inc., of which Dr. Lloyd is the Research Director, is developing a new generation of motorcycle helmets, utilizing a patented composite of shear-thickening non-Newtonian materials. Due to their nature, these advanced materials respond differently to linear and rotational forces, thereby allowing the helmet some independent rotational motion, effectively de-coupling the helmet from the head. This technology was demonstrated at NI Week (http://youtu.be/T591x950oRI) and shows great promise for protection against both blunt force trauma and traumatic brain injuries.
Given the choice of a helmet that protected against skull fracture and one which also provides protection against brain injury, which would you choose?
Dr. John Lloyd holds a PhD in Ergonomics from Loughborough University and is a Brain Injury Specialist. He is an expert in the field of brain injury biomechanics.
As a motorcycle enthusiast, John has clocked more than 250,000 miles and completed numerous training programs. Dr. Lloyd has served as a biomechanics expert on a variety of motorcycle accident cases.
Two helmeted motorcyclist were traveling on a rural state road when a tractor-trailer driver failed to see the bikes and made a left turn in front of them to enter a truck stop. The rider in the right track had little time to respond and collided head first into the box trailer. He was pronounced deceased at the scene.
The helmeted motorcyclist was wearing a non-compliant or ‘novelty’ helmet, which did not meet DOT motorcycle helmet standards (FMVSS 218). Opposing counsel claimed that had the biker been wearing a DOT-certified motorcycle helmet he may have survived the impact.
Motorcycle helmet expert, Dr. John Lloyd, was retained to evaluate and compare the protective performance of DOT-certified and novelty motorcycle helmets.
Based on a comprehensive motorcycle accident reconstruction it was determined that the impact speed of the rider was 45 to 50 miles per hour. Motorcycle helmet certification tests typically involve impact speeds of 13-17 miles per hour. Therefore a dedicated apparatus was constructed to generate higher impact speeds. Using a force-balanced twin pendulum apparatus, Dr. Lloyd was able to generate head impact speeds similar to those specific to the subject crash, yet preserve the standard DOT test methodology, thereby avoiding a Daubert challenge.
Eight DOT and non-DOT helmets were purchased for this study. Each was impacted once in the frontal region while fitted to an instrumented crash test dummy head. High speed data and video were acquired for each test.
Results demonstrate that, although the tested DOT-certified motorcycle helmets outperformed the tested novelty helmets, neither would provide adequate protection against head injuries, such as skull fractures, contusions and lacerations, or brain injuries, including hemorrhages or axonal injury in an impact of this magnitude.
Dr. Lloyd’s prior published motorcycle helmet studies demonstrate that while DOT-certified motorcycle helmets can reduce the risk of traumatic head injuries, typical helmets do not afford any protection against acute brain injury.
Helmets are intended to minimize blunt force trauma to the head, such as skull fracture, lacerations and contusions. Whereas risk of diffuse brain injuries, such as concussion, brain bleeding and axonal injuries are caused when brain tissue, nerves and blood vessels stretch and tear as the head moves suddenly but the brain lags behind. The type of brain injury is dependent on the magnitude of this strain and the time duration over which it acts on the brain.
Risk of focal head and brain injury is measured in terms of peak linear acceleration associated with impact, while risk of diffuse brain injury is measurable in terms of peak angular acceleration.
While helmets can prevent fatalities associated with penetrating head trauma, it may be argued that protection against diffuse brain injury is of paramount importance. After all, cuts, bruises and even bone fractures will heal, but brain injuries often have life long neurologically devastating effects.
Unfortunately, helmet testing standards addresses only the risk of blunt force trauma, not risk of brain injury.
Helmets may reduce the rotational forces acting on the brain. But since helmets are not currently certified according to their ability to protect against brain injury the level of protection is not standardized. Hence, it is possible to sustain catastrophic diffuse brain injuries, even while wearing a helmet.
As a biomechanics researcher, Dr. John Lloyd has dedicated his career to understanding the biomechanics of brain injuries. One objective of which is to develop a new generation of helmets for sports and motorcycling using “intelligent” materials that hold great promise for reducing the risk of traumatic brain injuries.
Dr. Lloyd’s biomechanics laboratory employs a specialized helmet testing apparatus for evaluating the risk of both head and brain injuries. This apparatus has been published in a peer-reviewer journal.
Using this apparatus, Dr. Lloyd, evaluates the linear and rotational forces associated with specific impact events, such as a motorcycle crash or sports injury, to determine whether an unhelmeted condition, or the type of helmet might have prevented the injury sustained. This apparatus has also been used to investigate whether a particular helmet failed to perform or did not meet scientifically-acceptable levels of protection.
Traditional testing of motorcycle helmets focuses on reducing the effect of linear impact forces by dropping them from a given height onto an anvil and measuring the resultant peak linear acceleration. According to the Federal Motor Vehicle Safety Standard (FMVSS) 218, commonly known as the DOT helmet standard, the test involves dropping a motorcycle helmet onto a flat steel and hemispherical anvil at an impact velocity of 6.0 m/s (13.4 mph). In general, if the resultant peak linear acceleration is less than 400G, the helmet is considered acceptable. Current motorcycle helmet testing standards do not incorporate measures of angular acceleration and therefore do not address whether any motorcycle helmet can provide protection against diffuse brain injuries, including concussion.
In 1995, the European Commission Directorate General for Energy and Transport initiated a Cooperative Scientific and Technical Research (COST) program to investigate Motorcycle Safety Helmets. Several agencies from Finland, the United Kingdom, France and Germany participated in this study, which compiled and analyzed data from 4,700 motorcycle fatalities in Europe, each year. The COST report [i] documents that 75% of all fatal motorcycle accidents involve head injury. Linear forces were present in only 31% of fatal head injuries, while rotational forces were found to be the primary cause in over 60% of cases.
Dr. Lloyd recently conducted independent testing of various motorcycle helmets utilizing a methodology that has been peer-reviewed [i] and has survived a Daubert motion for exclusion [ii]. The following figure presents peak angular acceleration results of repeated testing of various motorcycle helmets, including: (i) Voss novelty helmet, (ii) Bell shorty helmet, (iii) Daytona shorty helmet, and (iv) Bell full-face helmet, compared with an unhelmeted condition for impacts onto concrete at approximately 20mph. The red horizontal line on the figure indicates the 50% threshold for concussive trauma, as defined by Pellman et al [iii].
Results show that while a novelty or DOT approved motorcycle helmet will reduce the peak angular acceleration associated with a head impact relative to an unhelmeted condition, the level of protection is not sufficient to prevent diffuse brain injury in a typical motorcycle accident.
[i] Caccese V, Ferguson J, Lloyd J, Edgecomb M, Seidi M and Hajiaghamemar M: Response of an Impact Test Apparatus for Fall Protective Headgear Testing Using a Hybrid-III Head/Neck Assembly. Experimental Techniques, 2014.
[ii] Superior Court, Judicial District of Hartford, CT. Docket Number: HHD-CV-13-6043998-S. Case Caption: SHUMBO, JAKE Et Al v. K2 SPORTS USA Et Al. Order #227.86 regarding: 03/02/2015 Motion to Exclude Expert Testimony. Notice Issued: 07/09/2015
[iii] Pellman EJ, Viano DC, Tucker AM, Casson IR, Waeckerle JF: Concussion in professional football: reconstruction of game impacts and injuries. Neurosurgery 53(4): 799-812, 2003
[iv] COST-327 report of the European Commission Directorate General for Energy and Transport on Motorcycle Safety Helmets. (1999).
In December a movie titled “Concussion”, staring Will Smith will be released in theaters, chronicling the work and bravery of Dr. Bennett Omalu, who first discovered Chronic Traumatic Encephalopathy (CTE) as the consequence of repeated blows to the brain in football and attempts by the National Football League (NFL) to deny any causal link.
Impact loading involves a direct blow transmitted primarily through the center of mass of the head, resulting in extracranial focal injuries, such as contusions, lacerations and external hematomas, as well as skull fractures. Shock waves from blunt force trauma may also cause underlying focal brain injuries, such as cerebral contusions, subarachnoid hematomas and intracerebral hemorrhages.
