Characteristics And Mechanism Of Blast Injury Caused By Treading On A Landmine: Research In An Animal Model

BackgroundLandmine is a kind of explosive weapon that is placed in a shallow ground orunderground and that is detonated automatically or manually. Its manufacturing technologyand application is less demanding, so it is an ideal weapon of war to block the groundforces and it has been widely used and fully developed in the history of war. Prototype oflandmines can be dating back to the Song dynasty of China, then, it was known as"gunpowder bomb". Coming to the Ming Dynasty of China, it gradually evolved into amature arm named "artillery unit". Depended on the progress of various technologies ofhigh explosives and detonation, the early production of landmine got formulized andintelligentized, giving the birth of a huge landmine family which are able to adapt to warneed and battlefield environment. Anti-personnel landmine (APM) is of the largest numberof manufacture and laying. This kind of landmine is mainly designed for injuring individual,so its explosion equivalent is not very high. It is divided into three categories according toits destruction way: explosive, bounding, fragmentation landmine, among which, theexplosive landmine is now more commonly used and its main purpose is to make singlepawn maimed, largely impairing the overall combat effectiveness of the opponent groundforces. Meanwhile, in order to reduce the detectability of landmine, plastic landmines aremore and more common. Its plastic shell rapidly melted at high temperature along with theexplosion, rarely producing fragments and mainly forming the primary injury on thetriggers. Therefore, the study of the characteristics of the primary injuries caused bylandmine explosions becomes the key of the corresponding efficient treatment.Injured lower limb treading on a landmine has some particularities, that is outstandingdamage performance on the limb and its amputation is unavoidable, thus bring about aseries of economic and social problems to the injured and the whole country. So, it is alsourgent to seek the best treatment strategy to minimize the affect of landmine blast injuries.During nearly a century of exploring landmine explosion injury, although scholars have made considerable progress in landmine blast injury research, but their studies are manyfrom the experience of the treatment of war wounds and they are not appropriatelysupported by basic research for the lack of a stable and effective animal model. So thecharacteristics of primary injury of lower limbs and body are seldom systematicallydiscussed. Previous studies have found that landmine blast injuries of lower extremity areoften severe, but there is no uniform standard on the scope of debridement, the level ofamputation and other issues. Therefore, it is significant to pay attention to the study on theinjury characteristics of bones, blood vessels, nerves, muscle of lower limb triggering alandmine for further awareness, judgment on range of debridement, level of amputation,etc issues of affected lower limb. Landmine blast wave has a wide injury effect. Studyingthe injured features lower limb and exploring the damage features of main distant organ canprovide some references for formulating treatment strategies of patient treading on alandmine.Previous studies on the relationship between the movement and biomechanics and theinjury of lower limb triggering a landmine is not been clearly elaborated yet. The study ofsuch questions will be conducive to research on the therapy and landmine-protect strategyof lower limb treading on a landmine.ObjectivesThe experiment was aimed at establishing a simple and economical, reliable animalmodel by simulating the conditions and environment of lower limb treading on a landmine.Also The experiment was designed to observe the characteristics of injured lower limb anddistant organ6hours and12hours post injury, and further to explore the movements andbiomechanical characteristics of lower limb triggering a landmine explosion in order to findrisk factors for lower extremity injury during such processes, which may provide somepieces of basis for relevant clinical treatment and protection.Content and method1. Establishing an experimental model: New Zealand white rabbits were chosen asexperimental subjects. Walking posture of experimental animals was supported by atailor-made frame,600mg paper casing punctiform burster (explosion equivalent isapproximately1.09g) was used to simulate U.S. M14anti-personnel landmines (explosionequivalent was about29g). The burster was placed under the right hind foot of experimental animals and it was electrically detonated far away in order to simulate the scenarios thathuman treading on a landmine in a walking gait, and to:(1) Research local and distant injury effects of experimental animals under the analogstate. Compare the consistency with reference to previous studies and verify the stabilityand reliability of the injury model after repeated experiments.(2) Check the reasonability of the choice of animal weight and explosion equivalent atthe angle of the ratio of the weight and explosion equivalent.2. Applying the above animal model, follow characteristics of lower limb injuryinduced by treading on a landmine.(1) The general and microscopic injury characteristics of different tissues wasdescribed respectively.(2) Through semi-quantitative analysis of microscopic pathology and limb muscleactivity detection, partition the lower extremities treading on a landmine.(3) Through semi-quantitative analysis of microscopic pathology and limb muscleactivity detection, compare the damage extent of the different muscle groups.3. Applying the above animal models to study the systemic physiological indicators:vital signs, blood gas analysis, cardiac injury biomarkers (cTnI, cardiac troponin I; CK-MB,creatine kinase-MB), nerve injury biomarkers (NSE, neuron-specific enolase; MBP, myelinbasic protein), electrocardiogram (ECG), ultrasonic cardiogram (UCG) changes andpathological characteristics of major distant organs (brain, heart, lung, liver, kidney,intestine).4. Research movement and biomechanical characteristics of injured lower limb by themeans of high-speed photography and analyze the injury mechanism of lower limb andorgan, and explore the risk factors of injury.Result1. The established experimental animal model was simple and its wounding effect wasstable. Parts of the each animal’s lower limbs near the point of explosion of had singeingphenomena. Middle-lower shank of lower limbs was destroyed. The affected lower limbpresented four typical districts (Nechaev zoning protocol), that is a dispersion area,avulsion area, contusion area, commotion area. The injury incidence of major organ hadcertain similarity with associated clinical findings. 2. Lower extremity injury characteristics of the experimental animals treading onlandmine:(1) The general injury characteristics and plane differences of different tissue: theshank of lower extremity was damaged prevalently and the wounds were serious polluted,the lower section of tibial have open comminuted fractures, periosteal stripping, obliqueand exposed fracture end. Multisegmental and closed facture can occur possibly (1/15);muscle fascia was destructed and the blood clot remained in the gap, forming hematoma,muscle wound tract after the outer section getting a higher damage section than the innersection; cavity of knee joint have no obvious blood; the stump of experimental animals hasedema. Different sizes and the number of punctate hemorrhage irregularly distributed in theupper thigh of lower limb; nerve have bleeding epineurium and its injury cross-section washigher than the muscles and bones (P <0.05); gross injury appearance of the main vascularof the affected lower limb stump was not apparent. Digital subtraction angiography (DSA)examination revealed that large blood vessels of the limb stump away from the broken ends(about knee level) exists cramps, no obvious fracture.(2) Analysis of different partitions (Nechaev zoning protocol), microscopic pathologyand activity muscle of the lower extremity treading on a landmine: the muscle of sub-regionnecrosed over time and its activity declined progressively; muscle of avulsion area necrosedmost seriously (P <0.05)and remained a low level; muscle of contusion area necrosed withthe greatest increases over time(after about injury12h)(P <0.05), muscle activity in thisarea got the biggest drop; muscle of commotion area don’t necrose obviously; at the samesection (at a distance of about2-3cm away from the bone fracture end), tibialis anteriormuscle gained the heaviest injury and soleus gained the lightest injury (P <0.05).(3) New definition of the anatomy partition and reference of the corresponding clinicalmanagement on the lower extremity treading on a landmine: combined the general,microscopic pathology and muscle activity detection, the lower limb stump can be dividedinto three zones: dissociation tissue area (mainly characterize by soft tissue serious polluted,torn, bone fracture end and neighboring exposed for the lack of effective tissue coverage;the majority of muscle pathological necrosed and kept poor activity; there was no necessityfor reservation); contusion hematoma area (mainly characterize by obvious contusion andbleeding muscle tissue; muscle fascia damaged and hematoma formed in the gap, muscle necrosed progressively within12h after injury, muscle activity decreased fastestly over time;in the early (about6h after injury) processing stage, it should be treated as "danger zone"and retained or undertaken limited debridement); edema bleeding area (mainly characterizeby high degree of limb edema, irregular distribution of punctate hemorrhage in upper part;tightness should be considered as dressing with a tourniquet).3. Systemic injury characteristics:(1) Pathological features of major organs: central nervous system (CNS) had thelowest incidence of injury, only one lumbar spinal cord was found contusion hemorrhageunder the microscope (1/10)(P <0.05); injury incidence of lung was the highest (12/15)(P<0.05), but most of the injured lung show slightly and small flake bleeding was verycommon from the general view, micropathology of the lung manifest as interstitialpulmonary damage, hemorrhage, and edema; cardiac lesion occurred at fibrosis annulus ofheart valve (3/15), visible focal myocardial hemorrhage, epicardial bleeding can beobserved under the microscope; abdominal cavity organ injury rate was higher than thesolid organ (P <0.05), hollow organs (GI) had flaky bleeding performance and integralmembrane from general view, solid organs (liver and kidney) ruptured (3/15), intestinalsubmucosa bleeding is common under the microscope (6/15).(2) Physiological indicators Changes: heart rate and respiratory rate of experimentalanimals were much slower within one hour of post-injury compared with these of pre-injury(P <0.05), while arterial blood pressure had a short rise and blood gas analysis (PCO2, PO2,SO2, A-aDO2) did not change significantly at each time point.(3) Changes in serum biomarkers of myocardial injury: cTnI and CK-MB level ofexperimental animals of post-injury were significant higher than these of pre-injury (P<0.05).(4) Changes in serum biomarkers of neurological injury: NSE level of experimentalanimals of post-injury did not change compared with that of pre-injury (P <0.05), whileMBP level of post-injury increase remarkably (P<0.05).(5) ECG examination of experimental animal appeared sinus arrhythmia, ST segmentelevation, T wave inversion, while cardiac function showed no significant change within6hpost injury from the result of ultrasonic cardiogram (UCG).4. Kinematics and biomechanical characteristics of the lower limb triggering a landmine explosion:(1) Blast wave was detected in the chest and abdomen of animal, reachingcorresponding threshold of injury.(2) Movement of the injured lower limb of experimental animal: hit a mine inoccurred knee and hip of the lower limbs experimental animal had fast, extreme flexion thatwas followed by a rapid stretching after the simulative landmine explosion, forming aninjury mechanism of "whiplash" alike.(3) Acceleration difference of different parts of the lower limb triggering a landmineexplosion: there is a huge acceleration discrepancy between shank and thigh of affectedlower extremity (about10times).Conclusion1. The experimental animal model is characterized by simplicity, economy, andreliability.2. The stump of injured lower limb has partitions performance from gross pathology,named dissociation tissue zone, contusion hematoma zone, edema bleeding zone.3. The cross-section of nerve Injury is higher than that of bone and muscle injurycaused by treading on a landmine with lower extremity.4. The injury degree of different muscle group was various, tibialis anterior musclegained the heaviest injury and soleus gained the lightest injury.5. Injury of hollow organ is more common after treading on a landmine, but the injuryform is slight mostly and the change of cardiopulmonary function is not obvious.6. Landmine blast wave injury is an important injury factor of distant organ. Lowerlimb triggering a landmine explosion has rapid, overrange, passive motion at the momentsafter the explosion; the knee of affected limb has an important role in the energy bufferduring this process, so that its subsidiary structure gain a big injury risk.