SAFETY; PART IV
By Dr. Ken
For those of us who have a strong interest in helmets, it could be any number of factors, individually or in concert, that holds our interest. Helmet design and construction, helmet materials and shape, facemask attachments and configuration, painted or decaled individualization. Those who love helmets or who have found some sort of fascination with them, and I include myself among this group, very often see what appear to be obvious changes in the helmet as having a direct effect on the game of football. In some cases this has been true, and in others, the real value of the helmet is less clear. Safety is one of the areas of contradiction and debate.
In the first three installments of this lengthy article, I made clear that there are two "major" causative effects that have been held responsible for catastrophic cervical spine injury; axial loading and deceleration. Unfortunately, these are not the only encountered or possible causes of head and cervical spine injury and please note, the emphasis is on cervical spine injury which leads us to a few obvious questions. Is the helmet designed to protect the head? Is it designed to protect the cervical spine? Does the helmet protect the player from any injury and if so, why?
First, as was very clearly stated in P. David Halstead's article, HISTORICAL EVOLUTION OF FOOTBALL HEADGEAR, "the football helmet was and is designed to protect the areas of the wearer's head directly covered by the helmet from direct linear impact. The helmet WAS NOT DESIGNED, AND CANNOT BE DESIGNED IN THE CURRENT STATE OF THE ART, TO PREVENT INJURY TO OR PROTECT THE CERVICAL SPINE, OR SPINAL COLUMN OR THOSE AREAS OF THE NECK NOT COVERED BY THE HELMET, OR TO PREVENT INJURIES TO THE BRAIN WHICH RESULT FROM ROTATIONAL ACCELERATION." (emphasis mine). Many players, and I was one of them, assumed that the hard, plastic helmet would absorb or deflect impact forces to an extent that the head could and should be used as a battering ram, or point of initial contact in order to inflict maximum tackling or blocking efficiency or damage. This is just a fact of football life. The evolution of the helmet and its "space age materials," at least by mid-sixties standards, had a direct effect upon the coaching and playing techniques used and the assumptions made regarding possible injury.
ROTATIONAL ACCELERATION occurs from a nonlinear impact, one that is not "straight-on" or one that may be straight ahead but causes the head to then abruptly "turn" to one side. This extreme and rapid rotational force, or torque is governed by a number of factors. The greater the mass or weight of the object that is "turning" means that more force is generated. Thus, if a player is wearing a heavier helmet, more rotational force will be produced. The length of the moment arm is another factor that determines torque. If we have a ball tethered to a length of rope and swing it around, the ball that is attached to a longer piece of rope will produce more rotational force or torque, than one that is attached to a shorter piece of rope. Thus the size and weight of the helmet, head, neck length and other factors contributes to the degree of rotational force. An important element is also the length of time that contact is made and sustained. Head and neck injury are more likely and potentially more severe the longer that contact is sustained. Thus, if one is going to make head contact, the most rapid deflection of the blow and removal of the helmet from the opponent is a key factor.
We can immediately see the validity of Dr. Halstead's statement. With the primary factors of head and neck injury causation explained, it is obvious that the helmet, no matter how well constructed and thought out it might be, has many limitations with regard to preventing injury. So what can the helmet do? When we watch a high school, collegiate, or pro game, what is a realistic expectation? Straight ahead linear acceleration is well managed by the modern football helmet. The change in "hitting" rules and the changes in helmet design, materials, and construction manage these forces well. Rotational acceleration injuries that cause damage to the head and neck are not as well managed in part because a basic understanding of physics indicates that the helmet can "only do so much" and that under specific circumstances, torque is going to be produced that exceeds the ability of the body to withstand it, resulting in injury. Obviously, helmets cannot protect against all head injury and less so against cervical spine injury. Again quoting Dr. Torg's analysis that there are no "freak occurrences" that produce these injuries, if the player places his head and/or cervical spine in a position where it is exposed to certain specific forces, injury can be predicted.
Our next installment will discuss the factors in helmet construction and materials that can or should reduce or exacerbate injury upon contact.