The Injury Mechanism of Traumatic Amputation.

Traumatic amputation has been one of the most defining injuries associated with explosive devices. An understanding of the mechanism of injury is essential in order to reduce its incidence and devastating consequences to the individual and their support network. In this study, traumatic amputation is reproduced using high-velocity environmental debris in an animal cadaveric model. The study findings are combined with previous work to describe fully the mechanism of injury as follows. The shock wave impacts with the casualty, followed by energised projectiles (environmental debris or fragmentation) carried by the blast. These cause skin and soft tissue injury, followed by skeletal trauma which compounds to produce segmental and multifragmental fractures. A critical injury point is reached, whereby the underlying integrity of both skeletal and soft tissues of the limb has been compromised. The blast wind that follows these energised projectiles completes the amputation at the level of the disruption, and traumatic amputation occurs. These findings produce a shift in the understanding of traumatic amputation due to blast from a mechanism predominately thought mediated by primary and tertiary blast, to now include secondary blast mechanisms, and inform change for mitigative strategies.

Pelvic Protection Limiting Lower Limb Flail Reduces Mortality.

Pelvic blast injury is one of the most severe patterns of injury to be sustained by casualties of explosions. We have previously identified the mechanism of injury in a shock tube-mediated murine model, linking outward flail of the lower limbs to unstable pelvic fractures and vascular injury. As current military pelvic protection does not protect against lower limb flail, in this study we have utilized the same murine model to investigate the potential of novel pelvic protection to reduce injury severity. Fifty cadaveric mice underwent shock-tube blast testing and subsequent injury analysis. Pelvic protection limiting lower limb flail resulted in a reduction of pelvic fracture incidence from both front-on (relative risk (RR) 0.5, 95% confidence intervals (CIs) 0.3-0.9, p < 0.01) and under-body (RR 0.3, 95% CI 0.1-0.8 p < 0.01) blast, with elimination of vascular injury in both groups (p < 0.001). In contrast, pelvic protection, which did not limit flail, had no effect on fracture incidence compared to the control group and was only associated with a minimal reduction in vascular injury (RR 0.6, 95% CI 0.4-1.0, p < 0.05). This study has utilized a novel strategy to provide proof of concept for the use of pelvic protection, which limits limb flail to mitigate the effects of pelvic blast injury.

Mapping the Risk of Fracture of the Tibia From Penetrating Fragments.

Penetrating injuries are commonly inflicted in attacks with explosive devices. The extremities, and especially the leg, are the most commonly affected body areas, presenting high risk of infection, slow recovery, and threat of amputation. The aim of this study was to quantify the risk of fracture to the anteromedial, posterior, and lateral aspects of the tibia from a metal fragment-simulating projectile (FSP). A gas gun system and a 0.78-g cylindrical FSP were employed to perform tests on an ovine tibia model. The results from the animal study were subsequently scaled to obtain fracture-risk curves for the human tibia using the cortical thickness ratio. The thickness of the surrounding soft tissue was also taken into account when assessing fracture risk. The lateral cortex of the tibia was found to be most susceptible to fracture, whose impact velocity at 50% risk of EF1+, EF2+, EF3+, and EF4+ fracture types - according to the modified Winquist-Hansen classification - were 174, 190, 212, and 282 m/s, respectively. The findings of this study will be used to increase the fidelity of predictive models of projectile penetration.

A New Understanding of the Mechanism of Injury to the Pelvis and Lower Limbs in Blast.

Dismounted complex blast injury (DCBI) has been one of the most severe forms of trauma sustained in recent conflicts. This injury has been partially attributed to limb flail; however, the full causative mechanism has not yet been fully determined. Soil ejecta has been hypothesized as a significant contributor to the injury but remains untested. In this study, a small-animal model of gas-gun mediated high velocity sand blast was used to investigate this mechanism. The results demonstrated a correlation between increasing sand blast velocity and injury patterns of worsening severity across the trauma range. This study is the first to replicate high velocity sand blast and the first model to reproduce the pattern of injury seen in DCBI. These findings are consistent with clinical and battlefield data. They represent a significant change in the understanding of blast injury, producing a new mechanistic theory of traumatic amputation. This mechanism of traumatic amputation is shown to be high velocity sand blast causing the initial tissue disruption, with the following blast wind and resultant limb flail completing the amputation. These findings implicate high velocity sand blast, in addition to limb flail, as a critical mechanism of injury in the dismounted blast casualty.

Pelvic injury patterns in blast: Morbidity and mortality.

BACKGROUND: Pelvic trauma has emerged as one of the most severe injuries to be sustained by the victim of a blast insult. The incidence and mortality due to blast-related pelvic trauma is not known, and no data exist to assess the relative risk of clinical or radiological indicators of mortality. METHODS: The UK Joint Theater Trauma Registry was interrogated to identify those sustaining blast-mediated pelvic fractures during the conflicts in Iraq and Afghanistan, from 2003 to 2014, with subsequent computed tomography image analysis. Casualties that sustained more severe injuries remote to the pelvis were excluded. RESULTS: One hundred fifty-nine casualties with a 36% overall mortality rate were identified. Pelvic vascular injury, unstable pelvic fracture patterns, traumatic amputation, and perineal injury were higher in the dismounted fatality group (p < 0.05). All fatalities sustained a pelvic vascular injury. Pelvic vascular injury had the highest relative risk of death for any individual injury and an associated mortality of 56%. Dismounted casualties that sustained unstable pelvic fracture patterns, traumatic amputation, and perineal injury were at three times greater risk (relative risk, 3.00; 95% confidence interval, 1.27-7.09) to have sustained a pelvic vascular injury than those that did not sustain these associated injuries. Opening of the pubic symphysis and at least one sacroiliac joint was significantly associated with pelvic vascular injury (p < 0.001), and the lateral displacement of the sacroiliac joints was identified as a fair predictor of pelvic vascular injury (area under the receiver operating characteristic curve, 0.73). CONCLUSION: Dismounted blast casualties with pelvic fracture are at significant risk of a noncompressible pelvic vascular injury. Initial management of these patients should focus upon controlling noncompressible pelvic bleeding. Clinical and radiological predictors of vascular injury and mortality suggest that mitigation strategies aiming to attenuate lateral displacement of the pelvis following blast are likely to result in fewer fatalities and a reduced injury burden. LEVEL OF EVIDENCE: Prognostic, level III.

The risk of fracture to the tibia from a fragment simulating projectile.

Penetrating injuries due to fragments energised by an explosive event are life threatening and are associated with poor clinical and functional outcomes. The tibia is the long bone most affected in survivors of explosive events, yet the risk of penetrating injury to it has not been quantified. In this study, an injury-risk assessment of penetrating injury to the tibia was conducted using a gas-gun system with a 0.78-g cylindrical fragment simulating projectile. An ovine tibia model was used to generate the injury-risk curves and human cadaveric tests were conducted to validate and scale the results of the ovine model. The impact velocity at 50% risk (±95% confidence intervals) for EF1+, EF2+, EF3+, and EF4+ fractures to the human tibia - using the modified Winquist-Hansen classification - was 271 ± 30, 363 ± 46, 459 ± 102, and 936 ± 182 m/s, respectively. The scaling factor for the impact velocity from cadaveric ovine to human was 2.5. These findings define the protection thresholds to improve the injury outcomes for fragment penetrating injury to the tibia.

Restricting Lower Limb Flail is Key to Preventing Fatal Pelvic Blast Injury.

Pelvic vascular injury in the casualty of an explosive insult is a principal risk factor for increased mortality. The mechanism of injury has not previously been investigated in a physical model. In this study, a small-animal model of pelvic blast injury with a shock-tube mediated blast wave was utilised and showed that lower limb flail is necessary for an unstable pelvic fracture with vascular injury to occur. One hundred and seventy-three cadaveric mice underwent shock-tube blast testing and subsequent injury analysis. Increasingly displaced pelvic fractures and an increase in the incidence of pelvic vascular injury were seen with increasing lower limb flail; the 50% risk of vascular injury was 66° of lower limb flail out from the midline (95% confidence intervals 59°-75°). Pre-blast surgical amputation at the hip or knee showed the thigh was essential to result in pelvic displacement whilst the leg was not. These findings, corroborated by clinical data, bring a paradigm shift in our understanding of the mechanism of blast injury. Restriction of lower limb flail in the human, through personal protective equipment, has the potential to mitigate the effects of pelvic blast injury.

Analysis of isolated transverse process fractures sustained during blast-related events.

BACKGROUND: Personnel have sustained a range of devastating blast injuries during recent conflicts. Previous studies have focused on severe injuries, including to the spine; however, no study has specifically focused on the most common spinal injury-transverse process (TP) fractures. Although their treatment usually requires limited intervention, analysis of TP fractures may help determine injury mechanisms. METHODS: Data were collected from victims with spinal fractures who were injured in improvised explosive device attacks, from the UK's Joint Theatre Trauma Registry. The level and side of each TP fracture were recorded, as well as associated injuries, whether they were mounted or dismounted, and outcome (survivor or fatality). RESULTS: Most (80%) of the TP fractures were lumbar. More bilateral (both left and right fractures at the same level), and L5 TP fractures, were seen in fatalities than survivors. In the mounted group, lumbar TP fractures were statistically significantly associated with fatality, head injury, noncompressible torso hemorrhage, pelvic injury, and other spinal injuries. In the dismounted group, thoracic TP fractures were associated with head, chest wall, and other spinal injuries; and lumbar TP fractures were associated with pelvic and other spinal injuries. CONCLUSIONS: Different injury mechanisms of the TP in the mounted and dismounted groups are likely. Inertial forces acting within the torso due to rapid loading being transferred through the seat, or high intra-abdominal pressures causing the tensile forces acting through the lumbar fascia to avulse the TPs are likely mechanisms in the mounted group. Blunt trauma, violent lateral flexion-extension forces, or rapid flail of the lower extremities causing tension of the psoas muscle, avulsing the TP, are likely causes in the dismounted group. Isolated lumbar TP fractures can be used as markers for more severe injuries, and fatality, in mounted blast casualties. LEVEL OF EVIDENCE: Prognostic and epidemiological, level III.

Dismounted Blast Injuries in Patients Treated at a Role 3 Military Hospital in Afghanistan: Patterns of Injury and Mortality.

BACKGROUND: The purposes of this study are to define the pattern of injuries sustained by dismounted troops exposed to improvised explosive devices blasts treated at a Role 3 combat support hospital and to assess injury patterns and mortality associated with the mechanism. Our hypothesis was that mortality is associated with pelvic fracture, massive transfusion, high Injury Severity Score (ISS), multiple limb amputations, and transfer from a Role 2 facility. STUDY DESIGN: Retrospective study of 457 patients. Analysis performed on trauma registry data and systematic review of radiographs. RESULTS: 99.9% were men with a median age of 23 years and median ISS 10. 141 patients (30.9%) required massive blood transfusion. Limb amputations were frequently observed injuries, 109 of 172 amputees (63.4%) had a double amputation. 34 subjects (7.4%) had pelvic fractures; majority of pelvic fractures (88%) were unstable (Tile B or C). Risk factors associated with the overall mortality rate of 1.8% were an ISS greater than 15 (odds ratio: 11.5; 95% confidence interval: 1.38, 533; p = 0.009), need for massive transfusion (p < 0.0001), and the presence of a pelvic fracture (odds ratio: 7.63; 95% confidence interval: 1.13, 41.3; p = 0.018). CONCLUSIONS: Dismounted improvised explosive devices blast injuries result in devastating multiple limb amputations and unstable pelvic fractures, which are associated with mortality after initial trauma resuscitation at a Role 3 hospital.

A pre-clinical evaluation of silver, iodine and Manuka honey based dressings in a model of traumatic extremity wounds contaminated with Staphylococcus aureus.

Prevention of extremity war wound infection remains a clinical challenge. Staphylococcus aureus is the most common pathogen in delayed infection. We hypothesised that choice of wound dressings may affect bacterial burden over 7 days reflecting the current practice of delayed primary closure of wounds within this timeframe. A randomised controlled trial of 3 commercially available dressings (Inadine(®) (Johnson & Johnson, NJ, USA), Acticoat(®) (Smith & Nephew, Hull, UK), Activon Tulle (Advancis Medical, Nottingham, UK)) was conducted in a rabbit model of contaminated forelimb muscle injury. A positive control group treated with antibiotics was included. Groups were compared to a saline soaked gauze control. The primary outcome was a statistically significant reduction (p < 0.05) in tissue S. aureus at 7 days post-injury. Secondary outcome measurements included bacteraemias, observational data, whole blood determination, ELISA for plasma biomarkers, PCR array analysis of wound healing gene expression and muscle/lymph node histopathology. Antibiotic, Inadine and Acticoat groups had statistically significant lower bacterial counts (mean 7.13 [95% CI 0.00-96.31]×10(2); 1.66 [0.94-2.58]×10(5); 8.86 [0.00-53.35]×10(4)cfu/g, respectively) and Activon Tulle group had significantly higher counts (2.82 [0.98-5.61]×10(6)cfu/g) than saline soaked gauze control (7.58 [1.65-17.83]×10(5)cfu/g). There were no bacteraemias or significant differences in observational data or whole blood determination. There were no significant differences in muscle/loss or pathology and lymph node cross-sectional area or morphology. There were some significant differences between treatment groups in the plasma cytokines IL-4, TNFα and MCP-1 in comparison to the control. PCR array data demonstrated more general changes in gene expression in the muscle tissue from the Activon Tulle group than the Inadine or Acticoat dressings with a limited number of genes showing significantly altered expression compared to control. This study has demonstrated that both Acticoat(®) and Inadine(®) dressings can reduce the bacteria burden in a heavily contaminated soft tissue wound and so they may offer utility in the clinical setting particularly where surgical treatment is delayed.

Identifying future 'unexpected' survivors: a retrospective cohort study of fatal injury patterns in victims of improvised explosive devices.

OBJECTIVES: To identify potentially fatal injury patterns in explosive blast fatalities in order to focus research and mitigation strategies, to further improve survival rates from blast trauma. DESIGN: Retrospective cohort study. PARTICIPANTS: UK military personnel killed by improvised explosive device (IED) blasts in Afghanistan, November 2007-August 2010. SETTING: UK military deployment, through NATO, in support of the International Security Assistance Force (ISAF) mission in Afghanistan. DATA SOURCES: UK military postmortem CT records, UK Joint Theatre Trauma Registry and associated incident data. MAIN OUTCOME MEASURES: Potentially fatal injuries attributable to IEDs. RESULTS: We identified 121 cases, 42 mounted (in-vehicle) and 79 dismounted (on foot), at a point of wounding. There were 354 potentially fatal injuries in total. Leading causes of death were traumatic brain injury (50%, 62/124 fatal injuries), followed by intracavity haemorrhage (20.2%, 25/124) in the mounted group, and extremity haemorrhage (42.6%, 98/230 fatal injuries), junctional haemorrhage (22.2%, 51/230 fatal injuries) and traumatic brain injury (18.7%, 43/230 fatal injuries) in the dismounted group. CONCLUSIONS: Head trauma severity in both mounted and dismounted IED fatalities indicated prevention and mitigation as the most effective strategies to decrease resultant mortality. Two-thirds of dismounted fatalities had haemorrhage implicated as a cause of death that may have been anatomically amenable to prehospital intervention. One-fifth of the mounted fatalities had haemorrhagic trauma which currently could only be addressed surgically. Maintaining the drive to improve all haemostatic techniques for blast casualties, from point of wounding to definitive surgical proximal vascular control, alongside the development and application of novel haemostatic interventions could yield a significant survival benefit. Prospective studies in this field are indicated.

The outcome of British combat amputees in relation to military service.

BACKGROUND: The study aim was to determine the outcome, in relation to military service in UK military combat amputees. PATIENTS AND METHODS: Casualties were assessed at mean 2.4 years after injury and graded by a Functional Activity Assessment (FAA) ranging from 1 (fully fit) to 5 (unfit all duties) to score vocational functional outcome. ISS were calculated and the patients were categorised as having unilateral or multiple amputations. The Short Form-36 Health Survey (SF-36) was completed. RESULTS: Of the 52, 8 patients had left the forces by medical discharge, with 44 continuing to serve. 33 of the 44 had returned to work. 50 patients had FAA grades and were at least 7.6 months post-injury. No patients were graded as FAA1, 8 as FAA2, 18 as FAA3, 19 as FAA4 and 5 as FAA5. There was a trend for the FAA score to increase with injury severity, as measured by ISS i.e. vocational functional outcome was worse with more severe injuries, although this did not reach statistical significance (p=0.095). Multiple amputee patients had significantly higher FAA grades (p<0.001) and were all FAA 4 or 5. Of the 33 patients who had returned to work, 8 were FAA2, 12 FAA3 and 12 FAA4. The mean SF-36 scores for Physical Component Summary (PCS) increased significantly from 36.4 to 43.4 (p=0.001) with rehabilitation, while Mental Component Summary (MCS) was 53.0 and remained similar at 53.6 (p=0.987). MCS scores were similar in these patients to the normal population, 50 (SD 10). CONCLUSIONS: This study is the first to report the outcomes, with regards to return to work, of the UK military amputees injured in Afghanistan and Iraq Soldiers are surviving more severe and complex injuries than before and the majority are able to return successfully to military work. SF-36 PCS scores improve significantly with rehabilitation, and while MCS scores remain constant, the initial assessments are comparable with a normal population.

The effects of repeated dosing with 7.5% sodium chloride/6% dextran following uncontrolled intra-abdominal hemorrhage.

The use of hypertonic saline Dextran (HSD) for resuscitation following trauma has many potential benefits, especially for the treatment of military casualties, but there is very limited data on the responses following multiple dosing with this fluid. The effects of a second dose of hypertonic saline dextran for resuscitation of uncontrolled intra-abdominal haemorrhage were studied in an experimental model. Under general anaesthesia, 17 large white pigs (weight range, 48-67 kg) were subjected to uncontrolled hemorrhage produced by a tear in the common iliac artery. This resulted in a significant (P < 0.01) reduction of both mean arterial pressure (MAP) and cardiac index. One hour after injury, animals were assigned to one of three groups, receiving either no resuscitation (Group A), or two doses of HSD (at a dose rate of 4 mL/kg), administered either 1 and 4 h after injury (Group B) or 1 and 7 h after injury (Group C). Animals were monitored for 12 h post-injury. A second infusion of HSD caused a significant hypernatremia and diuresis (P< 0.01) in both Groups B and C. There was a non-significant rise in MAP in both treatment groups, and in Group B only, there was a significant increase in cardiac index (P= 0.014). It is concluded that repeat administration of HSD for the resuscitation of uncontrolled hemorrhage results in limited cardiovascular improvements, but that the metabolic sequelae are potentially detrimental to survival.