During a spring scrimmage in the afternoon on May 21, 2004, the RL Turner High School football team was finishing up their intra-squad scrimmage game. The play was called "33-counter" and Nat Little was playing defense at the linebacker position. The fullback broke through the line of scrimmage and that is where Nat make contact with the ball carrier. While Nat is tackling/wrapping up the ball carrier, a free safety goes low on the ball carrier and Nat comes over the top of the ball carrier and strikes the turf. These tackles happen all the time throughout the country at all levels. However, the result of Nat contacting the turf with his helmet, rendered him a quadriplegic.
Unfortunately, as the tackle occurred, Nat's helmeted head was flexed forward and an impact force was delivered to the top of his Riddell helmet. And, because Nat's helmet was poorly designed it was not capable of absorbing or attenuating enough of the force of the impact to prevent the compression of his cervical spine. Thus, when the force delivered through the helmet exceeded the tolerance of the cervical spine in compression (approximately 1,000 lbs. of force), his cervical spine fractured, causing a dislocation and disruption of the spinal cord. See illustration below.
The football helmet model worn by Nat Little was a Riddell VSR-4. Sadly, Nat is not the only high school player sitting in a wheel chair in Texas and unable to use his arms and hands because of this product's dangerous design.
PRINCIPLES OF HELMET DESIGN
A. History of Helmets
Helmets entered the sports scene in this country in the early days of football when athletes like Jim Thorpe, John (Paddy) Driscoll, and Red Grange began sporting leather caps. During the 1940's and 1950's, the football helmet underwent a metamorphosis leading to the development of a plastic helmet. Until the mid-sixties, the several companies involved with the design and sale of helmets produced products which were relatively unsophisticated. Until the 1960's, most helmets were designed without any real understanding of how this protective equipment benefits the user. In the 1960's, studies were made in the medical and engineering sciences to better understand how head and neck injuries occur from a blow to the head. Researchers began to uncover the nature of the physical forces required to cause serious head and neck injury. As a result, football helmet design underwent significant design changes. However, it remains true, even today, that the nature and extent of head and neck protection provided by helmets varies significantly based upon design and material parameters.
B. Safety Components of a Helmet
To understand the impact attenuation effectiveness of helmets used in football, we begin with a brief description of the basic safety components of a helmet: the shell and the liner.
1. The Shell
Virtually every safety helmet has a shell. The object of the shell is to provide a smooth hard outer surface, which resists penetration and serves to distribute an impact load over a large area. It is easy to understand that force is better managed if it has a wide area of distribution, rather than a local buckling zone. Thus, if a shell can effectively spread a localized impact load over a large segment of the shell, it will reduce the force transmitted to the liner (and perhaps to the head). Football helmet shells are generally built with thermoplastic material; thermoplastic is less rigid than fiberglass, used in motorcycle helmets, and it can buckle-in on impact.
2. The Liner
Most modern-day sports helmets include a shock absorbing liner. The shock absorbing liner in a helmet is positioned on the inside of the shell and designed to "manage" the force transmitted through the shell. As the second line of defense, the liner provides protection by compression under load. Its function is to absorb the force so that little, if any, load is transmitted to the player's head and spine. The energy of the impact is absorbed as the material compresses. How well a liner is designed to absorb energy is dependent upon its physical dimensions and characteristics of the liner. If, for instance, the liner is very dense/stiff and, therefore, does not crush readily under foreseeable impacts, then the primary force of the impact is passed along to the helmet wearer. Likewise, if the liner is easily depressed/crushed, then the force of impact is easily transmitted. Consequently, the correct choice of shock absorbing liner is one which manages predictable levels of force in foreseeable accidents by deforming in a controlled fashion. The liner, as it is compressed, absorbs the impact force over time (in milliseconds).
C. Neck Injury
As early as 1971, researchers published the results of detailed testing of football helmets and the design parameters considered vital to offer safe helmets to minimize serious injury in football. The researchers found that reasonably designed helmets will minimize the risk of spinal cord injury occurring when a football player is either tackled or makes a tackle and contact occurs with the top of the helmet. This research paper was supported by grants from the National Collegiate Athletic Association Committee on Competitive Safeguards and Medical Aspects of Sports. In describing the reasons for the investigation and development of a new helmet, it was stated that:
Another serious and tragic injury occurring in football is the cervical spine fracture with tetraplegia. The usual mechanism for such an injury is a blow to the vertex of the head with the neck in flexion.
This study is performed to simulate the forces present during the production of these serious injuries and compare the effectiveness of various types of protective football headgear in attenuating these forces.
... Helmets with varying types of outer shells and inner supports were applied to a plastic headform on a simulated neck and were impacted against an anvil. The conditions were approximated for two types of serious injuries. The method of production of an acute subdural hematoma and the creation of a cervical fracture with tetraplegia was simulated by occipital blows and vertex impacts, respectively.
Although all types of helmets attenuated the blows markedly,
compared to the bare headform, there was considerable
variation in the effectiveness between the helmet types."
These findings explain why the original NOCSAE standard in 1973 stated that newly adopted football helmet standards were expected to reduce the risk of head and neck injuries.
That conclusion was bolstered by a research paper published in 1978 by researchers at Wayne State University, including the Director of NOCSAE (a private agency that published the first nationally accepted football helmet standard) and entitled: An Assessment of Compressive Neck Loads Under Injury Producing Conditions. The authors recounted their studies to gauge the forces needed to cause spinal cord injury through compressive neck loading. Using test dummies, these scientists showed how this injury occurs, established a threshold for the force needed to cause this injury, and showed how the forces to the neck were reduced by almost any football helmet by 50% when compared to the neck forces in the same dummy head impact with a bare head.
Injury reference curves for axial compressive forces on the
neck were derived from impact tests of a spring-loaded tackling
block on football helmets. Results suggest that helmets, especially
those with resilient liners, reduce these forces.
This landmark study also showed significant variability in the level of protection provided by different model helmets. A few years later, Naval aviation experts reached the same conclusion that helmet design can reduce the risk of neck injury in the event of pilot ejection. These conclusions have been predicated upon the fact that the spine is viscoelastic, which makes it sensitive to compression injury in direct relation to the amplitude and duration of the force. In other words, injury to the spine is related to the position of the head and neck, the force of impact to the head and the time over which the spine sees the force. If the force to the spine exceeds approximately 1,000 lbs., when the neck is axially aligned (which requires impact to the top of the head when it is flexed forward), then compression injury can occur. In helmeted circumstances, compression of the spine occurs when either the helmet fails to sufficiently slow down/attenuate the transmission of energy along the "z" axis, or the force of impact is so severe that it has exceeded the energy attenuating capability of the helmet and the spine.
Analysis of Nat Little's Injury and The Performance of His Helmet.
Plaintiffs' expert, Dr. Richard Stalnaker, conducted two different type of helmet tests: Helmeted Head Drop Tests and 2) Helmeted Head Dummy Swing Tests. A description of each and his conclusions are provided below.
1) Helmeted Head Drop Test
A series of helmeted head drop tests were conducted by Dr. Stalnaker at his facility to evaluate the potential effectiveness of various football helmets to attenuate the impact forces to the top of the helmet. The testing was conducted using the NOCSAE test equipment and its protocol. The photos below demonstrate the testing setup.
This testing used several helmet models including a Riddell VSR-4, a Riddell VSR-3, a Schutt Air Power and a Schutt DNA model.
2) Dummy Swing Test
Once the helmet drop testing series was completed, Dr. Stalnaker then proceeded to conduct "dummy testing" to analyze the shock attenuating capacity of these same helmets to reduce the forces delivered to the dummy's neck in the axial direction. These tests were conducted by swinging the head, neck and torso of a Hybrid III dummy by cables into a rigid structure. The dummy was instrumented with full upper and lower neck transducers as well as a tri-axial accelerometer package at the head center of gravity. Below are photos of the dummy swing testing set-up.
The test instruments recorded information about the impact forces delivered to the neck. The tests were set up to produce impact conditions which are similar to those of the tackle play in question. Here is a summary of these test results:
Upper Neck Load
|Lower Neck Load|
Riddell VSR-4 with air (subjet helmet)
Riddell VSR-4 with air (subject helmet)
Riddell VSR-3 with air (alternative design)
Riddell VSR-3 with air (alternative design)
Schutt Air Power with air (altenative design)
Schutt Air Power with air (alternative design)
NOTE: The critical measure is the Exposure to Peak Compression in Excess of 900 lbs. Reference to Drop Height relates to the swing distance to the wall. The critical drop parameter is the 10.2 and 13.6 inch drop range.
Nat Little's injury is a classic compression neck fracture. This type of fracture occurs when the forces placed upon the neck in the axial direction are in the range of 900 lbs. to 1000 lbs. Riddell has known since 1978 that different helmets, by design, provide different levels of absorption which can therefore reduce the amount of compressive force delivered to the cervical neck. Nevertheless, instead of constantly striving to improve upon the top of the helmet design attenuation system, Riddell has haphazardly modified the top liner in different model helmets. And, Riddell has essentially ignored any opportunity to improve upon top of the helmet design performance to reduce the risk of compression fractures to the cervical spine.
Test results show that if Nat would have been wearing the Air Power model helmet or the Riddell VSR 3 model helmet, he would not have been injured.