Medical Science Publication No. 4, Volume 1
EXPERIMENTAL WOUND BALLISTICS*
CAPTAIN EDWARD W.A. OCHSNER, Jr., MC
In the experimental laboratory we have been attempting to develop astandard wound preparation comparable to a lethal war injury. Such a preparationwould permit one to: (1) study in detail, and under rigidly controlledconditions, the disturbed pathophysiology associated with wounding, and(2) to compare various types of therapeutic measures that may be appliedto the wounded.
The animal we have used in our studies is the goat, chosen primarilybecause of its size, docility and relative availability.
The animals have been wounded by two methods, each of which is comparableto a slightly different type of war injury. In one preparation a high-velocitymissile wound is produced by shooting the animal through the large posteriormuscle mass of the upper hind leg with a steel sphere (53.3 grains), travelingat a speed greater than 6,000 ft./sec. The missile produces external woundsof varying size on the lateral and medial aspect of each upper leg, buteven when the external wounds are very small, the damage done to the tissueswithin the legs is always extensive. The second preparation, i. e., theblast injury, is produced by a high-explosive charge called "tetryl"(2, 4, 6 trinitro-phenyl-methyl nitramine). A small cylinder (0.795 inchin diameter and 0.494 inch in depth) is taped to the lateral aspect ofeach upper hind leg. On top of and in direct contact with the explosiveis a detonator cap and the charge is detonated by 0.7 watt of electricity.The typical wound that results is superficially much larger than that producedby the high-velocity missile and even though there is no exit wound onthe medial aspect of the thigh, the tissue damage extends through the leg.
These are interesting preparations in that untreated animals never survivemore than 35 hours (with an average survival time of about 12 hours). Theyare all the more interesting when it is realized that blood transfusionswill not by themselves save these animals. It is hoped that these preparationswill be useful in attacking some of the problems raised by the observationand study of the wounded in the field. The current studies on this preparationwill not be reported
*Presented 20 April 1954, to the Course on Recent Advances in Medicine and Surgery, Army Medical Service Graduate School, Walter Reed Army Medical Center, Washington, D. C.
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at this time, since what I really intend to add to this conference isnot what happens as a result of wounding, but what happens during wounding.A concept of the wound mechanics is essential for the interpretation ofthe pathophysiology and an evaluation of any therapeutic procedures. Fortunately,many of these biophysical events have been defined for us by use of sparkshadow-graphs, microsecond x-rays and high-speed motion pictures.
The first principle to be understood is that in order for a wound tobe produced it is necessary for a missile to have a minimum striking velocity,this depending both on the character of the missile and the character ofthe tissue. The first major event occurring during wounding is shown byfigure 1, which is a spark shadow-graph showing a small missile strikingan air-water interface from above. This shows the hydraulic shock wavewhich is an extremely high-pressure front that spreads out radially withthe speed of sound in water (4,800 ft./sec.) from the point of impact ofthe missile. This is a physical entity and must not be confused with thephysiologic syndrome of shock which might occur subsequently. It is currentlybelieved that the shock wave causes no tissue damage except perhaps inthe presence of a gas-filled viscus.
FIGURE1. [Omitted]
SOURCE: Harvey, E. N., McMillen, J. H., etal.: Surgery 21: 218-239, 1947.
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The second and more important event is the development of a temporarycavity which forms behind the missile, beginning first as a cone-shapedspace which can be seen as the black area in figure 1, but which is betterillustrated by figure 2, which is a microsecond x-ray of a .45 caliberlead ball that has been fired into a 20 percent gelatin block from above.Twenty percent gelatin is used because it has the same consistency as muscle.It should be noted that it is the presented cross-sectional area of thebullet that forms the cavity and that most of the missile may float freein space never contacting the tissue. As the bullet flings tissue fromits path, it imparts energy to it and thus creates secondary missiles outof the body substances. The cone-shaped cavity now becomes cylindrical,producing local forces of the same destructive nature as would have beenproduced by an actual explosion within the tissue. The displacement isonly temporary, however, the tissues tending to snap back roughly intotheir former position and the cavity pulsating (that is, collapsing andre-expanding) a few times before finally disappearing. Figure 3 is a seriesof x-rays (exposure time-1 microsecond) taken at a varying number of microsecondsafter impact, illustrating these events. It also shows that the cavitycontinues to grow even though the missile
FIGURE 2.[Omitted]
SOURCE: Herget, C. M.: Wound Ballistics in Surgeryof Trauma-Ed.: W. F. Bowers. J. B. Lippincott Co., Philadelphia, 1953.
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has passed. The cavity concept will seem real, I am sure, if you willrefer to figure 4, which is a microsecond flash picture of our high-velocitywound preparation taken 2,000 microseconds after impact of the missile.
[Omitted]
SOURCE: Herget, C. M.: Wound Ballistics in Surgeryof Trauma-Ed.: W. F. Bowers. J. B. Lippincott Co., Philadelphia, 1953.
The maximum size of the temporary cavity is a function of the energytransfer and thus the velocity of the missile, the cross-sectional areapresented by the missile, and the elastic properties of the tissue. Figure5 shows the effect of cross-sectional area for .30
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SOURCE: Biophysics Div., Med. Lab., Army ChemicalCenter, Maryland.
SOURCE: Biophysics Div., Med. Lab., Army ChemicalCenter, Maryland.
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caliber bullet that was fired into a long gelatin block from the right.It began to tumble in the middle and presented its broadside to the left-handside of the gelatin block.
The phenomena that I have mentioned have all been demonstrated to occurduring missile wounding. What happens during wounding with a high explosiveis less understood. It is known, of course, that one starts out with asolid material and ends up with a gas. The actual process of disintegrationand the biophysical changes produced during this process need further elucidation.It is believed, however, that the same basic phenomena occur as in missilewounding. That is, there is the shock wave to begin with, and then thecavitational effect, perhaps myriads of cavities are produced as the solidcharge bursts into small burning particles which enter the body as individualmissiles until they burn up.
It should be easy to appreciate that the final wound seen by the surgeonmay not reveal the total amount of tissue damage incurred at the time ofwounding. After all, the permanent wound cavity represents only that tissuewhich has been permanently excavated or exteriorized. This can be demonstratedby figure 6, which shows the large radiolucent temporary cavity and thepermanent cavity which is injected with radio-opaque material. It takeslittle imagination to appreciate that there is considerable tearing andcrushing of tissues at a far distance from the permanent wound cavity.
In fact, in our standard wound preparations I have been impressed bythe amount of damage done to vessels, nerves, and even bones (note thefemur in figure 6)-although not directly hit by the missile. In the caseof muscles, it appears that for many inches from the permanent wound, theremay be damage in those portions of the muscle adjacent to the fascia, althoughthe rest of the muscle appears normal. This suggests, as might be expected,that the temporary cavity spreads largely along the fascial planes, andit emphasizes the desirability of opening the fascia in the surgical treatmentof these wounds.
As a result of the temporary cavity we can expect that not only destructionbut contamination will be found far from the clinically presenting wound.In fact, Dziemian (1) has demonstrated that during the tension phase ofthe temporary cavity foreign material is actually sucked into the woundand not carried in by the missile. It must also be realized (fig. 7) thatin the presence of armor, damage can be done by the temporary cavity eventhough the missile has been completely defeated. Proper offset of the bodyarmor will, of course, eliminate much of this danger, but while savingwounds armor may introduce occult wounds and other problems for the fieldsurgeon.
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FIGURE 6.[Omitted]
SOURCE: Herget, C. M.: Wound Ballistics in Surgeryof Trauma-Ed.: W. F. Bowers. J. B. Lippincott Co., Philadelphia, 1953.
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FIGURE 7.[Omitted]
SOURCE: Herget, C. M.: Wound Ballistics in Surgeryof Trauma-Ed.: W. F. Bowers. J. B. Lippincott Co., Philadelphia, 1953.
References
1. Dziemian, A. J., and Herget, C. M. Physical Aspectsof Primary Contamination of Bullet Wounds. Mil. Surgeon 106: 294-299,1950.
2. Harvey, E. N., Korr, I. M., Oster, G., and McMillen,J. H.: Secondary Damage in Wounding Due to Pressure Changes Accompanyingthe Passage of High Velocity Missiles. Surgery 21: 218-239, 1947.
3. Herget, C. M.: Wound Ballistics, p. 494 in Surgeryof Trauma-Ed: W. P. Bowers. J. B. Lippincott Co., Philadelphia, 1953.
