The mechanism of traumatic amputation of limbs by explosion is presented. A survey of blast casualties from Northern Ireland revealed that amputations through joints were very uncommon--the principal site was through the shaft of the long bones. Computer modelling of a bone exposed to blast forces reinforced the hypothesis developed from the casualty survey, that the primary mechanism of the bone injury was the direct coupling of the blast wave into the tissues. The fracture occurs from the resulting axial stresses in the bone, prior to limb flailing from the gas flow over the limb. The gas flow completes the amputation. Field trials employing a goat hind limb model have confirmed the hypothesis. Having identified the mechanism, concepts to develop protective clothing may now be proposed.
Death and injury due to terrorist bombings continue to exercise civilian and military surgeons alike. In this paper 828 servicemen killed and injured by explosions in Northern Ireland have been studied, using data stored in the Hostile Action Casualty System (HACS). Because of the nature of the conflict in Northern Ireland, the magnitude of each explosion and the distance of the victims from it are quite accurately known. The overpressure (blast loading) to which the victim was exposed can be estimated from the information on the HACS forms and standard tables, giving overpressures for a given change at a known distance. Using the HACS data, the numbers of injuries due to overpressure (primary blast injury), missiles energized by the blast (secondary injury), displacement of the victim by the blast wind (tertiary injury) and flash burn can be determined. Of the 828 servicemen involved in explosions, 216 were killed, most of them before any treatment could be instituted. Of the servicemen in the survey, 90 per cent were wearing body armour. Although body armour affords considerable protection from secondary missiles, it is unlikely to reduce the number of deaths due to primary blast injury.
The physical mechanism of blunt impact injuries to thoracic and abdominal viscera is often conveniently described simply in terms of "crush"--this is an over-simplification. Any impact to the torso does result in the rapid displacement of the body wall which may lacerate and contuse underlying viscera, but this simple explanation does not account for pathology at sites some distance from the contact point and does not adequately describe the dependence of the severity and location of injury upon the rate of energy transfer. Quite minor displacements of the body wall may produce serious injury if the body wall velocity is high. The motion of the body wall generates waves that propagate within the body and transfer energy to internal sites. The nature and properties of these waves are discussed in simple terms and the role of waves in the production of the characteristic injuries resulting from impact to the torso is presented.
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