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High-velocity gunshot wound through bone with low energy transfer
264
High-velocity gunshot wound through bone with low energy transfer J. C. Clasper’ and T. J. Hodgettsz Cambridge
Military
Hospital, Aldershot,
Injury, 1994, Vol. 25.264-266,
UK and 2Royal Army Medical College, Millbank,
May
Introduction It is recognized
that high-velocity missile wounds may only produce a low energy transfer wound, but that high-velocity wounds involving bone invariably lead to high energy transfer, with consequent shattering of the bone. A case is presented where a high-velocity bullet passed through a long bone with low energy transfer, and where additionally the wound track was not visible on a plain radiograph. This has not been previously described. The pathophysiology and management of high-velocity gunshot wounds is briefly discussed; emphasis is given to adequate surgical treatment and wound closure by delayed primary suture.
Case report A 23-year-old male soldier was brought by ambulance to the Accident and Emergency Department 15 min after being shot in the front of the right shoulder at point-blank range with a high-velocity 5.56 mm rifle round. Examination revealed an entry wound of approximately 6 mm diameter, with a surrounding powder burn, over the hurneral head anteriorly; there was a similar sized exit wound on the posterior humeral aspect. Pulses and sensation in the right arm were preserved. There were no other remarkable findings, and he remained haemodynamically stable. Intravenous opiate analgesia, and antibiotics (flucloxacillin 500 mg; benzylpenicillin 600 mg) were given. Tetanus immunity was confirmed. A radiograph of the right shoulder was interpreted as showing no bone injury, although soft tissue swelling was seen (FigureI). A chest radiograph was normal. At surgical exploration there was minima1 muscle damage. The bullet had passed through the humeral head, entering lateral to the lesser tuberosity and travelling superolaterally to exit through the back of the greater tuberosity (Figure2). Necrotic skin edges and dead muscle were excised at entry and exit wounds. The bone track was curetted and irrigated with hydrogen peroxide. The wounds were left open, unpacked and lightly dressed with fluBed gauzed; the dressing was secured by firm bandaging to immobilize the shoulder. Antibiotics were continued postoperatively. He returned to theatre at 5 days for wound inspection: no further debridement was necessary, allowing delayed primary suture. Two months 0 1994 Butterworth-Heinemann 0020-X303/94/040264-03
Ltd
London,
later he had made a full functional duties.
UK
recovery
and had returned
to
Discussion The damage inflicted by a bullet is a function of the energy transferred to the wound - this in turn is reiated to the inherent kinetic energy (KE) of the bullet, and its retardation within the tissues. As the available KE is the product of half the mass of the bullet and the square of its velocity, a doubling of the velocity will produce a four-fold rise in energy. Hence the development of light rounds that can be fired at very high velocity, to maximize available energy and potential tissue damage. The degree of retardation of the bullet depends on the density of the tissue through which it travels, together with the size, shape and stability of the round. When bone is struck it is usual for all or most of the energy of the bullet to be transferred (Rutherford et al., 1989); the bone commonly shatters, as may the bullet, and both may form secondary fragments. Despite the ‘rifling’ of a gun barrel to improve the stability of a bullet, the bullet will still see-saw about its short axis (yaw) and spin around its long axis (precession and nutation); should the bullet strike the body perpendicularly (0” yaw), it may be more stable and only impart 10-20 per cent of its available KE (Kirby, 1981). A low-velocity (C 350m/s) missile, such as from a handgun, produces injury by direct tissue crushing and laceration leaving a permanent cavity, but the damage is confined to the wound track. High-velocity missiles, such as from a military rifle, also result in a permanent cavity but characteristically there is extensive tissue damage distant from the wound track; for a few milliseconds the tissues continue to move away from the wound track after the bullet has passed, forming a temporary cavity some 30-40 times the diameter of the permanent cavity. As the temporary cavity collapses, bacteria and debris are sucked into the wound and widely disseminated. The conditions are ideal for the proliferation of anaerobic organisms, and specifically Clostridium tetani and Clostridium welchii: penicillin is the prophylactic antibiotic of choice, and human tetanus immunoglobulin (250-500 IU intramuscularly) should be given with tetanus toxoid (separate sites) if more than 10 years have elapsed between vaccines, or there is any uncertainty of immune status (Department of Health, 1992). Muscle is more susceptible to cavitation than bone,
Case reports
265
Figure 1. Plain radiograph of the right shoulder - soft tissue swelling is seen, but the wound track through the humerus is not visible.
and where muscle bulk is low damage will be limited. In this patient it is evident that there can only have been low energy transfer. Suggested reasons would be bullet stability on penetration (no in-flight irregular movements as fired at point-blank range), low muscle bulk (at this anatomical site) and short wound track in which to impart energy. It may be important that the bullet passed through mostly cancellous bone. No cavitation effects were evident and the wound was equivalent to that caused by a low-velocity injury. Radiographs cannot be relied upon to exclude bone injury. The temptation to trivialize such injuries when there is little visible surface injury must be avoided - they are highly contaminated wounds which require adequate exposure, toilet and removal of necrotic tissue. Delayed
Figure 2. Plain radiograph of the right shoulder track is demonstrated by the wound probe.
- the missile
266
primary suture is the preferred
Injury: International Journal of the Care of the Injured (1994) Vol. 25INo.
surgical technique, whereby a missile wound that has received appropriate debridement and toilet, and remains clean, is suitable for suturing after 3 to 5 days. In the meantime, the wound is dressed with lightly fluffed gauze to promote free drainage. This technique will minimize the risk of postoperative infection. The treatment suggested here relates to high-velocity missile wounds, A low-velocity missile will always produce a low energy transfer wound and in some circumstances may not-require extensive exploration - indeed, the missile may sometimes be left in situ. However, it is safer to assume that the missile was of high velocity, unless one is certain of the ballistics. Although high-velocity missiles are recognized to produce low energy transfer wounds, it may be perilous to adopt a nonoperative approach in the absence of extensive clinical experience.
4
References Department of Health (1992) Immunisation against Infectious Disease. London: HMSO, 40. Kirby Maj. Gen. N. G. (ed.) (1981) Field Surgery Pocket Book. London: HMSO, 1. Rutherford W. H., Illingworth R. N., Marsden A. K., Nelson P. and Redmond A. D. et al. (eds) (1989) Accident and Emergency Medicine. Edinburgh: Churchill Livingstone, 188. Paper accepted 3 February
1994.
Reqtresfsfor Teprinfs should be addressed to: Major J. C. Clasper FRCsEd DipIMC RCSEd, Registrar, Department of Orthopaedics, Cambridge Military Hospital, Aldershot GLJll 2AN, UK.
High-velocity gunshot wound through bone with low energy transfer J. C. Clasper’ and T. J. Hodgettsz Cambridge
Military
Hospital, Aldershot,
Injury, 1994, Vol. 25.264-266,
UK and 2Royal Army Medical College, Millbank,
May
Introduction It is recognized
that high-velocity missile wounds may only produce a low energy transfer wound, but that high-velocity wounds involving bone invariably lead to high energy transfer, with consequent shattering of the bone. A case is presented where a high-velocity bullet passed through a long bone with low energy transfer, and where additionally the wound track was not visible on a plain radiograph. This has not been previously described. The pathophysiology and management of high-velocity gunshot wounds is briefly discussed; emphasis is given to adequate surgical treatment and wound closure by delayed primary suture.
Case report A 23-year-old male soldier was brought by ambulance to the Accident and Emergency Department 15 min after being shot in the front of the right shoulder at point-blank range with a high-velocity 5.56 mm rifle round. Examination revealed an entry wound of approximately 6 mm diameter, with a surrounding powder burn, over the hurneral head anteriorly; there was a similar sized exit wound on the posterior humeral aspect. Pulses and sensation in the right arm were preserved. There were no other remarkable findings, and he remained haemodynamically stable. Intravenous opiate analgesia, and antibiotics (flucloxacillin 500 mg; benzylpenicillin 600 mg) were given. Tetanus immunity was confirmed. A radiograph of the right shoulder was interpreted as showing no bone injury, although soft tissue swelling was seen (FigureI). A chest radiograph was normal. At surgical exploration there was minima1 muscle damage. The bullet had passed through the humeral head, entering lateral to the lesser tuberosity and travelling superolaterally to exit through the back of the greater tuberosity (Figure2). Necrotic skin edges and dead muscle were excised at entry and exit wounds. The bone track was curetted and irrigated with hydrogen peroxide. The wounds were left open, unpacked and lightly dressed with fluBed gauzed; the dressing was secured by firm bandaging to immobilize the shoulder. Antibiotics were continued postoperatively. He returned to theatre at 5 days for wound inspection: no further debridement was necessary, allowing delayed primary suture. Two months 0 1994 Butterworth-Heinemann 0020-X303/94/040264-03
Ltd
London,
later he had made a full functional duties.
UK
recovery
and had returned
to
Discussion The damage inflicted by a bullet is a function of the energy transferred to the wound - this in turn is reiated to the inherent kinetic energy (KE) of the bullet, and its retardation within the tissues. As the available KE is the product of half the mass of the bullet and the square of its velocity, a doubling of the velocity will produce a four-fold rise in energy. Hence the development of light rounds that can be fired at very high velocity, to maximize available energy and potential tissue damage. The degree of retardation of the bullet depends on the density of the tissue through which it travels, together with the size, shape and stability of the round. When bone is struck it is usual for all or most of the energy of the bullet to be transferred (Rutherford et al., 1989); the bone commonly shatters, as may the bullet, and both may form secondary fragments. Despite the ‘rifling’ of a gun barrel to improve the stability of a bullet, the bullet will still see-saw about its short axis (yaw) and spin around its long axis (precession and nutation); should the bullet strike the body perpendicularly (0” yaw), it may be more stable and only impart 10-20 per cent of its available KE (Kirby, 1981). A low-velocity (C 350m/s) missile, such as from a handgun, produces injury by direct tissue crushing and laceration leaving a permanent cavity, but the damage is confined to the wound track. High-velocity missiles, such as from a military rifle, also result in a permanent cavity but characteristically there is extensive tissue damage distant from the wound track; for a few milliseconds the tissues continue to move away from the wound track after the bullet has passed, forming a temporary cavity some 30-40 times the diameter of the permanent cavity. As the temporary cavity collapses, bacteria and debris are sucked into the wound and widely disseminated. The conditions are ideal for the proliferation of anaerobic organisms, and specifically Clostridium tetani and Clostridium welchii: penicillin is the prophylactic antibiotic of choice, and human tetanus immunoglobulin (250-500 IU intramuscularly) should be given with tetanus toxoid (separate sites) if more than 10 years have elapsed between vaccines, or there is any uncertainty of immune status (Department of Health, 1992). Muscle is more susceptible to cavitation than bone,
Case reports
265
Figure 1. Plain radiograph of the right shoulder - soft tissue swelling is seen, but the wound track through the humerus is not visible.
and where muscle bulk is low damage will be limited. In this patient it is evident that there can only have been low energy transfer. Suggested reasons would be bullet stability on penetration (no in-flight irregular movements as fired at point-blank range), low muscle bulk (at this anatomical site) and short wound track in which to impart energy. It may be important that the bullet passed through mostly cancellous bone. No cavitation effects were evident and the wound was equivalent to that caused by a low-velocity injury. Radiographs cannot be relied upon to exclude bone injury. The temptation to trivialize such injuries when there is little visible surface injury must be avoided - they are highly contaminated wounds which require adequate exposure, toilet and removal of necrotic tissue. Delayed
Figure 2. Plain radiograph of the right shoulder track is demonstrated by the wound probe.
- the missile
266
primary suture is the preferred
Injury: International Journal of the Care of the Injured (1994) Vol. 25INo.
surgical technique, whereby a missile wound that has received appropriate debridement and toilet, and remains clean, is suitable for suturing after 3 to 5 days. In the meantime, the wound is dressed with lightly fluffed gauze to promote free drainage. This technique will minimize the risk of postoperative infection. The treatment suggested here relates to high-velocity missile wounds, A low-velocity missile will always produce a low energy transfer wound and in some circumstances may not-require extensive exploration - indeed, the missile may sometimes be left in situ. However, it is safer to assume that the missile was of high velocity, unless one is certain of the ballistics. Although high-velocity missiles are recognized to produce low energy transfer wounds, it may be perilous to adopt a nonoperative approach in the absence of extensive clinical experience.
4
References Department of Health (1992) Immunisation against Infectious Disease. London: HMSO, 40. Kirby Maj. Gen. N. G. (ed.) (1981) Field Surgery Pocket Book. London: HMSO, 1. Rutherford W. H., Illingworth R. N., Marsden A. K., Nelson P. and Redmond A. D. et al. (eds) (1989) Accident and Emergency Medicine. Edinburgh: Churchill Livingstone, 188. Paper accepted 3 February
1994.
Reqtresfsfor Teprinfs should be addressed to: Major J. C. Clasper FRCsEd DipIMC RCSEd, Registrar, Department of Orthopaedics, Cambridge Military Hospital, Aldershot GLJll 2AN, UK.