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Leatt-Brace and Similar Devices

 

The Leatt-Brace is promoted to protect the motorcyclist’s cervical vertebral column. However, this device may produce “dangers” of its own. Of course, a device cannot be considered “dangerous”: it is motorcycling which is dangerous. However this device could convert relatively innocuous or survivable injuries into injuries with greater morbidity and death.

Although claims are made that injuries to the vertebral column will be reduced if the Leatt-Brace is used, there is no possible way of substantiating this claim. Controlled trials are simply not possible. The tumult of a motorcycle accident and the multiple variables cannot be replicated.  It is certainly not possible to re- visit those injuries and introduce categories as controlled trials.

Motorcycle accidents on the road are difficult to reconstruct.  Race-track injuries are well documented, but these are usually slither-tumble injuries. On modern race tracks the impact against stationary objects is relatively infrequent. Rarely do these become projection or impact injuries and only occasionally “ride-over” injuries.

Motorcycle accidents on the road, however, are more likely to be collisions resulting in impact and projection injuries. Even in a slither event, the rider on the road often hits stationary or moving objects.

Therefore this claim by Leatt remains supposition,  based on a primitive, linear reasoning which is:

The neck is potentially vulnerable in that it is not protected by a strongly mechanical sheath, unlike the way that the lumbar, thoracic, and intra-cerebral spinal cord is protected. Let us then put a  brace about it, and so “protect” it.

Wish it were that easy.

This linear reasoning appears not to have fully comprehended the functional anatomy of the mechanisms of the cervical vertebral column, which makes it invalid.

If my head is fully protected by a helmet, is it not logical to extend that protection to my neck?

Firstly one must ask what protection the helmet offers.

There can be no debate that the crash-helmet reduces head injury and death in motorcyclists, a worthwhile but not universal protection.

The helmet prevents many penetrating, abrasive and direct contact facial injuries But it offers little protection against rotational injuries (which produced diffuse axonal and brainstem lesions) and these injuries might be increased  by the helmet’s inertia if body rotation decreases rapidly.

The helmet reduces deceleration injuries to some extent but concussive and contra-coup injuries will be reduced only by a margin when deceleration is from speeds of excess of 50 km an hour.

Direct blows on the top of the head (axial compression injuries) are a common cause of spinal injuries. These might be increased in some circumstances by the weight of the helmet

The Leatt-Brace will not prevent axial compression injuries: But it could promote or worsen that injury, because it interferes with evasive actions

There is some evidence that helmets reduce injuries to the cervical vertebral column, but this is poorly documented and the types of spinal injury which are reduced by the use of a protective headgear are not well analysed.

 

How do we protect ourselves from external forces?

Humans, like most other mammals, have exceedingly good “energy dissipating devices”. What this means is that there are highly sophisticated neuromuscular circuits designed to protect the individual from that universal enemy, the force of gravity. It is therefore possible for the human to fall, sometimes heavily, and sustain little or no damage. This is well illustrated in contact sports, notably rugby and professional wrestling.  The sophistication of the martial arts has allowed specific techniques of energy dissipation to be trained into participants early in their martial arts career.

In American and rugby football, energy dissipation or “break fall” is not usually trained: Instead the players rely on intuitive and inherent capacities to protect themselves from injury when their balance is perturbed. Some fondly imaginings this is a “conscious” mechanism: it is not. It is not possible in the time available to rationalise which strategies should be employed. With very few exceptions, there is no time to anticipate the vectors of destructive forces. Humans survive by the blessings of ”hardwired” and intuitive mechanisms [1]

That these mechanisms of energy dissipation exist is easily demonstrated. Most individuals could jump from a table to the floor and suffer no injury. There would be no outward expression of the kinetic forces, such as loud sounds, generation of heat or light or damage. On the other hand, if a 75 kg facsimile of that individual in granite was pushed from the table the forces of falling would convert to  sound, heat, light and damage. Another example: Robots can do much, even mimic running. But robots do not have the energy dissipating mechanisms of humans. A robot on a rugby field would not survive the first tackle or even, perhaps, the first nudge, without damage. Watch a cat fall.

 

How is this done?

The human frame, in its vertical axis is designed as a complex zigzag from the toes to the skull. Each of the angles of these zigzags is controlled by muscle allowing these zigzags to be compressed, concertina-like. During this compression, muscles response near instantly by tensioning, and by using their inherent energy allow the external energy to be slowly and safely dissipated.

Rotational movements are also used to dissipate energy, and allow the limbs to flex, reducing their lever-arm length, or tucking the limbs beside or behind the trunk.

There seem to be priorities in the methods of protecting the body. The head brain and eyes seem to have a priority re. protection. The hands and mouth are next in this triage and the feet follow.

Why a high head and a thin neck?

It is no coincidence that the head is placed high on the body. Better surveillance is an obvious benefit. Perhaps more important, by its height the brain is maximally protected from injury. Whilst accepting that the phrasing which I use is teleological, the “purpose” of the mobile and relatively thin neck is that it allows the head a great freedom of movement and consequently the maximum capacity to protect the brain from jarring or other forces (including rotation) which could damage the enclosed brain. It is well-recognised that, when people fall, the head is rapidly moved away from a potential point of contact.

Consider the tumult such as occurs in motorcycle accidents. This freedom to move the head will likely be the critical component to the broader “energy dissipating mechanisms” and its contribution to protecting the head from impact.

Where the body is thrown towards an impacting surface, even a few centimeters of intuitive movement of the head away from the potential point of impact (perhaps transferring impact to the shoulder or the upper limbs) could prevent severe injury to the head. If this flexibility is lost and the ability to move the head is prevented (as it would be with the Leatt-Brace) that latitude is lost.  . Even distances of one or 2 cm might be critical in preventing severe brain damage. Immobilisation by a neck brace might therefore result in severe injury

Whilst the Leatt-Brace could protect the neck from flexion injuries, by imposing immobility it is equally likely to make damage to the brain more common and more serious than any neck injury would have been.

Other functions of the head.

Inasmuch as movement of the head plays an important role in protecting the brain, the head also plays a vital role in the overall posture of movement, particularly movement during falling. The head weighs the equivalent of two bricks and functions as a counterbalance. The capacity to move the head rapidly and induce “coupling” dynamics in the physics of equilibrium is immensely important. If the head is restrained, for example by the Leatt- Brace, it becomes impossible to posture the body in space. This use of the head as a counter balance is well illustrated by springboard divers  to control backwards and forward somersaults. Without a free range of neck movement it would be impossible for the diver to obtain a posture safe for entry into water, or the gymnast to land. Try jumping from a step wearing a Leatt-Brace! Make sure that it is not more than a step, since jumping from a height of even half a meter, wearing the Leatt-Brace, could produce a severe injury including a fracture of the base of the skull.

I am not aware that this concept is discussed in standard textbooks of medicine, and for most medically and biologically trained people this is not considered.

Is the neck especially vulnerable?

The cervical vertebral column could be mistakenly considered a “vulnerable” area region. This might be because spinal cord injuries invoke highly emotive responses because they are potentially so incapacitating and incurable. However, taken overall injuries to the cervical vertebral column are less common than injuries to the brain. There are also specific situations where the vertebral column is at higher risk One is the diving into shallow water which has produced this devastating injury many thousands of times. The reason is that the diver does not expect to strike the head, and none of the “head / neck protection” mechanisms are recruited. Injuries to this vital part of the vertebral column also occur in road traffic accidents generally. These are far less specific and the victims range from pedestrians through to individuals who have survived motor vehicle accidents, and finding themselves inverted and held by seatbelts, then suffers catastrophic injury when a “helpful” individual releases the seatbelt: the victim then falls onto the (inverted) roof of the vehicle, and suffers cervical spinal cord injury.

How can we find out more?

Because it is so difficult to get sufficient information from road traffic accidents a possible model could be rodeo injuries, which are well documented. A number of rodeo injuries are caused by falls from height, such as would happen to a projected motorcyclist after hitting a stationary object.

In order to illustrate the effects on the neck of these types of falls, illustrations of Gauchos can be used to analyse the mechanics of the injury. Even more important is the analysis of the fail safe mechanisms which are spontaneously recruited by the rider. It is improbable that any rodeo rider would allow himself to be restricted by a Leatt-Brace – and it would be highly unethical to even suggest this.

 

illustration. It is apparent that this rider is already laterally flexing his head and rotated the left, whilst rotating the trunk to the right to allow his right hand to block the possible point of head impact. The probabilities are that he will strike his shoulder or shoulders and it is likely that he might escape injury free. However, had he been wearing a restrictive neck brace, he would not be able to posture his head in this protective way and the chances of him having a head injury would be considerably increased if not inevitable.

Is there a way to protect this vulnerability of the cervical vertebral column, and perhaps the brain as well? This seems possible and the author has researched this, including the compounded locus of movement of the neck and the neck-on-head, in much detail. That research has included a detailed investigation into the (complex) locus of movement and angular velocities of the cervical vertebral column. A later paper will consider an appropriate design for a protective neck brace.

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