Saturday, April 30, 2011

Concussion, Loss of Consciousness, and Injury Science - Pt 1

How many times have you had it explained to you that concussion or loss of consciosness (LOC) is due to forces being applied to the head resulting in the brain impacting with the skull? As we will see, this theory is 'now considered obsolete and somewhat discredited.'

I've been researching the effect of different types of mechanical loads (externally applied forces) on the tissues of the body for my injury science and pain book which is intended to facilitate the understanding and study of the techniques of the martial arts and physical violence generally. In doing so, I came across the subject of brain injury.

Jack Jallo and Christopher M. Loftus, in Neurotrauma and Critical Care of the Brain, explain that mild brain injury (MBI) has many names, including concussion. This and an as yet unspecified number of blogs will look at his discussion on MBI.

MBI can result from head contact or movement of the head without head contact. For instance, shaken-baby syndrome involves shaking a baby which results in various degrees of brain injuries. Derrick Pounder recently reported the first case of shaken-adult syndrome when he reported on an autopsy performed on a 30-year old Palastinian who had died at the hands of the Israeli General Security Service. They were interogating him by violently shaking him. You'll be pleased to know that this interogation method has been included in the approved list of interogation methods by the United States.

Jallo and Loftus provide the following with regards to the forces involved with or without head contact:
Regardless of how they are delivered, these forces result in inertial (or accelerative) loading and have two main components. The first is linear or translational acceleration/deceleration and is defined as movement of the head in a straight line through its centre of gravity. An example of this type of force would be a straight blow to the face. The second is angular or rotational acceleration/deceleration. This type of force occurs when the head is accelerated tangentially and moves through an arc around its centre of gravity. A blow to the chin is an example of this type of acceleration. ... It has been demonstrated ... that it is the angular acceleration the is primarily responsible for LOC. Linear force, on the other hand, resulted in facial contusions and hemorrhage but no LOC.

Application of inertial loading via translational or rotational acceleration has at least four consequences:

1. Impact between the surface of the brain and the skull due to rotatoray inertial loading of the head.
2. Tracton on brain stem neurons due to forceful movement of the hemispheres.
3. Depression of the skull bone associated with deformation of the underlying brain tissue and the propogation of intracranial pressure waves.
4. Acceleration of the head about the axis of the neck.

Several theories exist as to how the combination of these forces results in MBI.
We'll look at these theories in the next blog, including the now discredited theory that is so often espoused martial arts instructors. But it is interesting that a rotational component is found to be necessary for LOC and other diffuse brain injuries.

Injury, within injury science, is defined as the exposure to physical energy, including kinetic energy.
Discussion of the biomechanics of MBI would not be complete without the examining the effects of kinetic energy transfer. Why is it much harder to produce a concussion in an animal model when the head is fixed versus free? The principles and behaviour of kinetic energy must be considered when answering this question. When the head is not mobile or is in contact with another surface, the kinetic energy will flow through the cranium and into the object that it is in contact with. This explains why a victim of an assault who keeps his head still by maintaining it in contact with the ground or a wall is unlikely to lose consciousness: the energy is transferred through the cranium to the object it is in contact with leaving the brain unharmed. This information can be used to an athelete's advantage. A player in contact sports can minimise the effects of an impact by tensing the muscles of the neck before the collision occurs. This results in decreased head mobility and increases the dispersion of the kinetic energy recieved from the cranium to the rest of the body. Conversely, not tensing the neck muscles before an impact because it is not anticipated has been demonstrated to increase the risk of MBI. Based on this information the importance of neck strengthening in boxers and football players becomes obvious.
The reader of this blog may understand the technical aspects of the passages extracted from Jallo and Loftus to varying degrees, but they should readily appreciate that the injury science theories and concepts have a great deal to offer to the understanding and study of the techniques of the martial arts and all forms of physical violence in general.

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Your comments make my work all the more relevant as I use them to direct my research and theorising. Thank you.