High Velocity Missle Injury

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High VelocityAn Experimental

Missi!e InjuryStudy of the Retentive Forces of Tissue

Joseph J. Amato, MD, Boston, MassachusettsLawrence J. Billy, MD, St . Louis, MissouriNoel $. Lawson, MD, Detroit, MichiganNorman M. Rich, MD, Washington, DC

As early as 1848 Hugiuer noted that high velocitybullets used in the Paris street fights producedwounds of an explosive nature [I]. He theorizedthat the severity of the wound was proportional tothe water content of the tissues. However, woundswithin similar tissues varied from extremely minorto severe. Woodruff [2] in 1898 questioned the in-consistent character of high velocity bullets in pro-ducing tissue destruction and first described theformation of the temporary cavity in high velocitymissile wounds. Wilson [3] in 1921 also noted thebizarre behavior of the high velocity bullet and theexplosive effect within certain tissues.

Cavitation is a feature of all missile wounds.This phenomenon is the momentary lateral expan-sion of the tissue within the missile tract caused bya deposition of kinetic energy. It is now knownthat the severity of the wound depends not only onthe behavior of the missile within tissues, but alsoon the histologic character of the tissues beingstruck.

Previous observations of high velocity injurieshave been made from war casualties and from lab-oratory studies of the composite wound [4-61. Thedeductions made from those observations haveFrom the Biomedical Department. Bioohvsics Laboratorv. U.S. EdaewoodArsenal, Maryland, and ihe Departmint-of Cardiothorac/c Surgery. NewEngland Medical Center and Tufts University School of Medicine, Boston,Massachusetts.Reprint requests should be addressed to Dr Amato, Department ofCardiothoracic Surgery, Tufts-New England Medical Center, 171 HarrisonAvenue, Boston, Massachusetts 02111.Presented at the Fifty-Fourth Annual Meeting of the New England Sur-gical Society, Portsmouth, New Hampshire. September 27-29, 1973.

been taken to be characteristic of individual organinjury, and for the most part, the description ofthe mechanism of injury has been correct. The ini-tial experiments conducted at Edgewood Arsenal,using high speed photography and roentgenogra-phy, have dealt with the study of isolated vascularinjuries [ 7-91, whereas further experiments havebeen conducted to evaluate the pattern of injury inisolated organs such as muscles, liver, and bone.The purpose of this paper is to demonstrate theevents that occur within each tissue after high ve-locity bullet wounding, and to discuss briefly theinteraction between the disruptive forces of themissile and the retentive forces of the tissue.

Material and Methods

Individual experiments were conducted for each ofthe tissue studies. Although each of the preparationsused was different as will be described, th e equipmen tand ma terials were similar.

Muscle. The hind limbs of twenty anesthetized dogswere utilized to study the sequence of events in musclewounding. Skin flaps were created to expose the musclemass. Injury to the femur was avoided to prevent bonefragmentation.Lioer. The liver from freshly slaughtered goats was re-moved and suspended by the ligaments prior to wound-ing. Numerous attempts to study injury to the liver invivo were performed; however, detailed docum enta tionof this met hod was impossible. Angiogram s of th e isolat -ed livers were obtained by injecting Hypaque@ into theappropriate blood vessels.

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I,cing. I,uni:s were removed from ten goats and imme-diately inflated wit.h air to return them to their normalanatomic configuration. The pulmonary arteries wereinjected with Hypaque just prior to wounding.

Hone. Femurs were obtained from freshly slaughteredcalves. To create an environment that would clearlyvisualize bone destruction, the femurs were individuallyembedded in a clear gelatin which was allowed to solidi-fy. thereby simulating the properties of muscle.

To insure identical wounds in the foregoing experi-ments, an 0.2.5 inch sphere weighing 16 gr was used. In-juries were inflicted on these tissues at a striking veloci-ty of approximately 3,000 feet per second. Comparativeinjuries with lower velocities of 1,000 feet per secondwere also made. The events in the sequence of injurywere documented by high speed motion picture photog-raphy using a Red Lake Hycam camera at 3,750 to 4,500frames per second. The Flexitron X-Ray System capa-ble of delivering up to 1,000 amps at 30 kv of anode po-tential producing pulses of less than one 0.1 Fsec in du-ration was used for both roentgenographic and angio-graphic smdies.

Figure 1. Roentgenogram of the temporary cavity formedin muscle by a low velocity missile at 1.000 feet per sec-ond.

parenchyma (specific gravity 0.4 to 0.5) by show-Results ing disruption of the blood vessels tilled wit,h Hv-paque. (Figure 8.)

The sequence of injury to the isolated organswas demonstrated in each of the experiments. Themuscle (specific gravity 1.02 to 1.04) preparationsbest demonstrate each of the phases of low andhigh velocity injury. The low velocity woundcreates a-direct pathway of destruction with verylittle motion within the surrounding tissues. (Fig-ure 1.) A small temporary cavity can be seen whenthe missile strikes muscle tissue at 1,000 feet persecond. However, when muscle is struck at 3,000feet per second, the initial movement of impactdemonstrates the phenomenon of tail splash,which is the backward hurling of destroyed tissue.(Figure 2.) Within microseconds, a large space isformed within the wound tract; this is referred toas the temporary cavity. The maximal diameter ofthe temporary cavity is approximately thirty timesthe size of the original missile. (Figures 3 and 4.)The tissue undulates for 5 to 10 msec and comes torest as the permanent tract.

Liver (specific gravity 1.01 to 1.02) is similar tothe density of muscle. However, both the tempo-rary cavity formed by a high velocity missile strik-ing at 3,000 feet per second (Figures 5 and 6) andthe resulting permanent tract (Figure 7) are largerthan those of muscle.

Although previously never visualized andthought possibly to be nonexistent [IO], a tempo-rary cavity is formed within the lung tissue by a

Both high speed photography and roentgenogra-phy demonstrated large temporary cavities in thefemurs that had been injured by the high velocitysphere. Bone has a high density with a specificgravity of 1.11 or greater depending on the degreeof ossification within the bone. As the missile pen-etrates the bone, fragmentation occurs (Figure 9)with the fragment.s going toward the edges ~)f helarge cavity. As undulation occurs, these fragmentsreturn to the center of the cavity and the majorityremain there. After a lag phase, a number of thesebone spicules are seen to move forward in the di-rection of the missile.

missile striking at 3,000 feet per second. Angio- Figure 2. The phenomenon of tail splashing is demon-grams demonstrate a small cavity within the lung strated in tissue a few milliseconds after impact.

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Figure 3. Roentgenogram demonstrating the maximalsize of the temporary cavity in muscle tissue caused bya high velocity missile.Comments

Ballistics, the study of the motion of a projec-tile, is divided into three phases: interior, exterior,and terminal. Interior ballistics deals with the mo-tion of the bullet within the gun barrel. Exteriorballistics, the second phase, studies the flight ofthe bullet to the target. The final phase, terminalballistics, is the study of the bullet within the tar-get. The study of the motion of a bullet within thetissues is termed wound ballistics. As tissues arestruck by a missile, multiple disruptive forcescombine to produce tissue destruction. The majorforces consist of the velocity, the mass, and thechange in shape or presented area of the bulletwhen it reaches the tissue. The most importantforce is the velocity of the missile within thetissues. The initial velocity on impact is called

Figure 4. High speed photograph of the temporary cavitywithin muscle tissue caused by a high velocity bullet.

striking velocity. If the bullet leaves the tissue, theremaining velocity is called the residual velocity.The effective velocity of the injury is the differ-ence between the two velocities (VI - V,). The ki-netic energy (KE) imparted to the tissues ex-pressed in foot pounds can be written:

KE = M(V12 - V22)/2 gwhere M equals mass and g equals gravity. If smallamounts of energy are released within the tissue,as in the low velocity wound, destruction will beconfined to the pathway of the bullet. The energyreleased by high velocity missiles forms initialshock waves with pressure of up to 100 to 200 at-mospheres, imparting momentum to the tissuesboth forward and laterally. These tissues acceler-ate in an outward direction creating a large spaceknown as the temporary cavity, its duration beingonly 10 to 30 msec. The tissues undulate and un-dergo stretching and compression. Because of theheterogeneity and varied density of the tissues,there is added mechanical damage due to theshearing effect between these tissues.

The second disruptive force is the mass of thebullet. Increase in mass will cause proportional in-crease in tissue destruction. A third disruptiveforce is the shape of the bullet or the change inpresented area on striking the tissues. The bulletmay present itself in a direct nose-on position onstriking with a large amount of yaw, or tumbling.If the degree of yaw is minimal at impact, the bul-let will travel quickly through the tissue and exitwith a greater residual velocity. If there is a largeangle of yaw, or if the bullet tumbles, the area ofthe bullet presenting to the tissues is larger andthe pathway of the bullet is longer and wider,causing marked retardation of the bullet withinthe tissues. Deformation of the bullet or fragmen-tation will likewise increase the presented area andcause tumbling within the tissues. Consequently,more energy is deposited, creating greater damagePI.The retentive forces that combat the disruptiveforces vary with the individual tissues. The char-acteristic pattern of injury is determined by thedensity of tissues combined with the degree ofelasticity and cohesion within these tissues. Mus-cle and liver are tissues with similar densities.Muscle tissue is composed of cells with a contrac-tile force embedded within a structured connectivetissue framework, that is, endomysium, perimys-ium, and epimysium. The liver is surrounded by afibroelastic membrane. The existing connectivetissue is limited to the arteries, veins, lymphatics,

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Figure 6. The maximal temporary cavity within liver tis-sue caused by a high velocity bullet (high speed motionpicture photography).

Figure 5. Venogram of the liver showing the maximal for-mation of the temporary cavity in high velocity missile in-jury.

Figure 7. Permanent missile tract within liver tissuecaused by a missile fired at 3,000 feet per second.

Figure 8. Pulmonary angiogram demonstrating the tem-porary cavity formed in lung parench,yma by a high ve-locity bullet.

and bile ducts. The further supporting structures nal position. Krauss [9] in 1957 has shown thatof the reticuloendothelial system are composed of there is only a small area of actual cellular destruc-fine reticular fibers that add little supporting tion surrounding the temporary cavity immediate-strength to the liver. It was found that the energy ly after injury. Although the muscle tissue hasabsorbed per centimeter of both liver and muscle been displaced approximately 3 cm radially, only atissue t,raversed is essentially identical [9]. How- 5 mm rim of destroyed tissue is seen. Although aever, the formation of the temporary cavity within zone of extravasation and capillary disruption ap-the liver and the resultant permanent tract are pears, it is difficult to determine whether most ofboth larger. Both muscle and liver, when first the suhsequent changes might, not be caused bystruck by a high velocity missile, exhibit a phe- impaired blood supply [9]. It is apparent that. thenomenon called tail splashing. This phenomenon cohesive structure of the liver is less than that ofis similar to a body of water being struck with a muscle. Consequently, when struck with a high ve-rock. On injury, the firmly harnessed cellular com- locity missile, the entire pathway of the temporaryponents of muscle expand laterally forming a large cavity loosens cells from their cellular supportingtemporary cavity, and except for the central por- structures during undulation of the cavity. Thetion of the wound tract, they return to their origi- permanent missile tract approximates the tempo-

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Figure 9. The high velocity bullet fragments the bonewithin the temporary cavity.rary cavity in size because of the volume of tissuelost during injury.

As discussed and demonstrated in detail in aseparate report [IO], the passage of a high velocitymissile through lung does create a temporary cavi-ty that is smaller and less impressive than that ofmuscle or liver tissue. The elastic fibers within thespongework of lung parenchyma absorb the energyand recoil so that the missile tract is hardly per-ceptible.

Although the question has been raised as towhether bone, because of its brittle character,reacts to these injuries by producing a true tempo-rary cavity, the cavitys formation was clearly visi-ble. Bone is dense tissue composed of calcium saltsembedded within an organic intercellular sub-stance of collagen. The critical velocity for fractur-

Figure 10. The exit wound formed by a high velocity mis-sile that has struck bone. Fragments of bone are seenexiting the wound as secondary missiles.

ing bone is approximately 200 feet per second. Thefemurs struck with high velocity missiles demon-strate a severe amount of destruction but are heldwithin the surrounding framework of periosteumand muscle connective tissue. Most interesting isthe phenomenon of bone fragments visualizedmoving forward in the direction of the bullet.These bone spicules act as secondary missiles,creating further destruction within the tissues.With the deformation or fragmentation of missileor bone, the skin at the exit site becomes shatteredand torn by these multiple fragments. (Figure 10.)Summary

Wound ballistics is defined as the study of themotion of missiles within the tissues. To under-stand tissue destruction we must realize that theseverity of injury depends on an intricate balanceof the action of the missile and the reaction of thetissues. The mass, shape, and velocity of the bulletand the change in presented area are the majorfactors that render destruction to the tissues. l

Our studies of the mechanism of injury to vari-ous tissues such as the muscle, liver, lungs, andbone have demonstrated graphically the formationof a temporary cavity within these tissues and thesequence of events that occur within these isolatedtissues. The size of the temporary cavity is propor-tionate to the specific gravity of the tissues and tothe severity of the injury. However, the elasticityand cohesiveness of the tissue counteract the ex-pansion of the wound tract and absorb the deposi-tion of kinetic energy by the missile. The tissueswith a more cohesive structure and with largeamounts of elastic tissue consequently demon-strate a greater resistance to injury.References1.2.3.4.5.6.

7.

8.9.

10.

Horsely V: The destructive effects of small projectile. Nature50: 106, 1894.Woodruff CE: The causes of the explosive effect of modernsmall caliber bullets. NY MedJ67: 593, 1898.Wilson LB: Dispersion of bullet energy in relation to wound

effects. Milit Surg 159: 249, 1921.Harvey EN, Butler EC, McMillen JH: Mechanism of wounding.War Med8: 102, 1945.Rich NM: Vietnam missile wounds evaluated in 750 patients.Milt Med 133: 9, 1968.DeMuth WE: Bullet velocity and design as determinants ofwounding capacity: an experimental study. J Trauma 6:222, 1966.Amato JJ, Billy LJ, Gruber RP, Lawson NS, Rich NM: Vascu-lar injuries: an experimental study of high and low velocitymissile wounds. Arch Surg 101: 167, 1970.Herget CH: Wound ballistics. Surgery of Trauma (BowersWB, ed). Philadelphia, Lippincott, 1956.Krauss M: Studies in wound ballistics: temporary cavity ef-fects in soft tissues. Milit Med 121: 221, 1957.Amato JJ: Temporary cavitation in high velocity pulmonarymissile injury. In manuscript.

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High Velocity Missile Injury

Discussion

Thomas Perry, dr (Providence. RI): Could you relateto us rhe approximate velocity of the various gun mis-siles that we ordinarily see in practice?

F. A. Simeone (Providence, RI): I want to congratu-late l)r Amato on his excellent presentation of an impor-tant subject in a field that we do not like to talk aboutbut that will be with us for some time to come.

Doctor Amato has illustrated the dramatic changesthat a missile produces in matter as it expends its kinet-ic energy. A very important practical question is raisedby the demonstration, namely, how much viable tissuehas been rendered nonviable by the missile? For exam-ple, the advantage of delayed primary closure of a con-tused wound is based on the fact that at the time of clo-sure, some five days after wounding, nonviable tissuehas declared itself and is easily distinguished from livingtissue. This distinction is difficult to make with certain-ty at the time of injury.

I want to ask Dr Amato if he has made observationsthat would indicat.e the extensiveness of the necrosis oftissues surrounding the temporary cavitation. In otherwords, is there a relation between the severity of the vio-lence and the depth at which living tissue has beenkilled by the formation of the temporary cavities? Thiskind of information would be of obvious practical im-portance.

J. Amato (closing): Thank you Dr Perry. To answerDr Simeone, yes, there is a relation between the severityof the violence and the depth at which the cells within

the tissues have actually heen killed by the formation otthe temporary cavity. Although I cannot recall all of thedata at this time, our laboratory investigators as well asother investigators had shown that in muscle tissue, forexample, the actual area of destruction of cells aroundthe temporary cavity measured approximately 5 mm indepth at the time of injury. The remaining destructionwhich became demarcated within hours and days is ac-tually, I believe, a result of loss of vascularity t.o thetissues that had been stretched within the temporarycavity.

In answer to Dr Perrys question, in the science of bal-listics there are several measurements of velocity.Muzzle velocity is the velocity at which the bullet leavesthe gun. Striking velocity is that velocity at which thebullet strikes the target, and residual velocity is that ve-locity at which the bullet leaves the target. The most im-portant measurement is the effective velocity which isthe striking velocity minus the residual velocity. In mostinstances, when speaking of the velocity, one is referringto the muzzle velocity. The ordinary .22 short has a ve-locity of 900 feet per second. The .25 caliber travels at,800 feet per second. The .38 caliber has a velocity of ap-proximately 925 feet per second, whereas the .45 caliberhas a velocity of 850 feet per second. As these missilestravel though air, both gravity and air drag slow them toa lower striking velocity. It is also interesting to knowthat it takes a velocity of approximately 175 feet persecond to penetrate the skin. When you consider thatthe velocity of an M-16 is 3,259 feet per second, the dif-ference in tissue destruction caused by these missiles iseasily understood.

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High Velocity Missle Injury