Iain Gibb

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.

Primary blast lung injury prevalence and fatal injuries from explosions: insights from postmortem computed tomographic analysis of 121 improvised explosive device fatalities.

BACKGROUND Primary blast lung injury (PBLI) is an acknowledged cause of death in explosive blast casualties. In contrast to vehicle occupants following an in-vehicle explosion, the injury profile, including PBLI incidence, for mounted personnel following an external explosion has yet to be as well defined. METHODS This retrospective study identified 146 cases of UK military personnel killed by improvised explosive devices (IEDs) between November 2007 and July 2010. With the permission of Her Majesty’s Coroners, relevant postmortem computed tomography imaging was analyzed. PBLI was diagnosed by postmortem computed tomography. Injury, demographic, and relevant incident data were collected via the UK Joint Theatre Trauma Registry. RESULTS Autopsy results were not available for 1 of 146 cases. Of the remaining 145 IED fatalities, 24 had catastrophic injuries (disruptions), making further study impossible, leaving 121 cases; 79 were dismounted (DM), and 42 were mounted (M). PBLI was noted in 58 cases, 33 (79%) of 42 M fatalities and 25 (32%) of 79 DM fatalities (p < 0.0001). Rates of associated thoracic trauma were also significantly greater in the M group (p < 0.006 for all). Fatal head (53% vs. 23%) and thoracic trauma (23% vs. 8%) were both more common in the M group, while fatal lower extremity trauma (7% vs. 48%) was more commonly seen in DM casualties (p < 0.0001 for all). CONCLUSION Following IED strikes, mounted fatalities are primarily caused by head and chest injuries. Lower extremity trauma is the leading cause of death in dismounted fatalities. Mounted fatalities have a high incidence of PBLI, suggesting significant exposure to primary blast. This has not been reported previously. Further work is required to determine the incidence and clinical significance of this severe lung injury in explosive blast survivors. In addition, specific characteristics of the vehicles should be considered. LEVEL OF EVIDENCE Epidemiologic study, level IV.

Mandibular fractures in British military personnel secondary to blast trauma sustained in Iraq and Afghanistan

Blast trauma is the primary cause of maxillofacial injury sustained by British service personnel on deployment, and the mandible is the maxillofacial structure most likely to be injured in combat, but there are few reports about the effect of blast trauma on it. The Joint Theatre Trauma Registry identified all mandibular fractures sustained by British servicemen secondary to blast injury between 1 January 2004 and 30 September 2009. These were matched to corresponding hospital notes from the Royal Centre for Defence Medicine (RCDM) for those evacuated servicemen and autopsy records for those who died of wounds. Seventy-four mandibular fractures were identified in 60 servicemen. Twenty-two soldiers were evacuated to the RCDM and the remaining 38 died from wounds. Fractures of the symphysis (39/106, 37%) and body (31/106, 29%) were more common than those of the angle (26/106, 25%) and condyle (10/106, 9%). This pattern of injury differs from that of civilian blunt trauma where the condyle is the site that is injured most often. Those fractures thought to result from the blast wave itself usually caused simple localised fractures, whereas those fractures thought to result from fragments of the blast caused comminution that affected several areas of the mandible. The pattern of fractures in personnel injured while they were inside a vehicle resembled that traditionally seen in blunt trauma, which supports the requirement for mandatory wearing of seat-belts in the rear of vehicles whenever tactically viable. All mandibular fractures in servicemen injured while in the turret of a vehicle had evidence of foreign bodies or radio-opaque fragments as a result of their exposed position. Many of these injuries could therefore be potentially prevented by the adoption of facial protection.

Frequency and relevance of acute peritraumatic pulmonary thrombus diagnosed by computed tomographic imaging in combat casualties.

BACKGROUND Posttraumatic pulmonary embolism is historically diagnosed after clinical deterioration within the first week after injury. An increasing prevalence of immediate and asymptomatic pulmonary embolism have been reported in civilian and military trauma, termed hereafter as acute peritraumatic pulmonary thrombus (APPT). The objective of this study was to define the frequency of APPT diagnosed by computed tomographic (CT) imaging in wartime casualties. An additional objective was to identify factors, which may be associated with this radiographic finding METHODS A 1-year retrospective cohort analysis conducted using the US and UK Joint Theater Trauma Registries performed to determine the prevalence of and risk factors for the diagnosis of APPT in casualties admitted to Bastion Hospital, Afghanistan. APPT imaging characteristics were collected, and demographics, injury severity and mechanism, and risk factors were included in the analysis. Logistic regression was used to identify factors independently associated with APPT. RESULTS APPT was found in 66 (9.3%) of 708 consecutive trauma admissions, which received a CT chest with intravenous contrast as part of their initial evaluation. Diagnosis of APPT at the time of injury was made in 23 patients (3.2%), while thrombus was detected in 43 additional patients (6.1%) at the time of reexamination of CT images. Of the APPTs, 47% (n = 31) were central, 38% (n = 25) were segmental, and 15% (n = 10) were subsegmental. Forty-seven percent (n = 31) had bilateral APPT. Logistic regression found presence of deep venous thrombosis on admission (odds ratio, 5.75; 95% confidence interval, 2.44–13.58; p < 0.0001) and traumatic amputation (odds ratio, 2.53; 95% confidence interval, 1.10–5.85; p = 0.030) to be independently associated with APPT. All APPTs were felt to be incidental and likely would not have required interventions such as anticoagulation or vena caval interruption. CONCLUSION This report is the first to characterize acute, peritraumatic pulmonary thrombus in combat injured. Nearly 1 in 10 patients with severe wartime injury has findings of pulmonary thrombus on CT imaging, although many instances require repeat examination of initial images to identify the clot. APPT is a phenomenon of severe injury and associated with deep venous thrombosis and lower-extremity traumatic amputation. Additional study is needed to characterize the natural history of peritraumatic pulmonary thrombus and the indications for anticoagulation or vena cava filter devices. LEVEL OF EVIDENCE Epidemiologic and prognostic study, level III.

Blast Injury in the Spine: Dynamic Response Index Is Not an Appropriate Model for Predicting Injury.

BackgroundImprovised explosive devices are a common feature of recent asymmetric conflicts and there is a persistent landmine threat to military and humanitarian personnel. Assessment of injury risk to the spine in vehicles subjected to explosions was conducted using a standardized model, the Dynamic Response Index (DRI). However, the DRI was intended for evaluating aircraft ejection seats and has not been validated in blast conditions.Questions/purposesWe asked whether the injury patterns seen in blast are similar to those in aircraft ejection and therefore whether a single injury prediction model can be used for both situations.MethodsUK military victims of mounted blast (seated in a vehicle) were identified from the Joint Theatre Trauma Registry. Each had their initial CT scans reviewed to identify spinal fractures. A literature search identified a comparison population of ejected aircrew with spinal fractures. Seventy-eight blast victims were identified with 294 fractures. One hundred eighty-nine patients who had sustained aircraft ejection were identified with 258 fractures. The Kruskal-Wallis test was used to compare the population injury distributions and Fisher’s exact test was used to assess differences at each spinal level.ResultsThe distribution of injuries between blast and ejection was not similar. In the cervical spine, the relative risk of injury was 11.5 times higher in blast; in the lumbar spine the relative risk was 2.9 times higher in blast. In the thoracic spine, the relative risk was identical in blast and ejection. At most individual vertebral levels including the upper thoracic spine, there was a higher risk of injury in the blast population, but the opposite was true between T7 and T12, where the risk was higher in aircraft ejection.ConclusionsThe patterns of injury in blast and aircraft are different, suggesting that the two are mechanistically dissimilar. At most vertebral levels there is a higher relative risk of fracture in the blast population, but at the apex of the thoracic spine and in the lower thoracic spine, there is a higher risk in ejection victims. The differences in relative risk at different levels, and the resulting overall different injury patterns, suggest that a single model cannot be used to predict the risk of injury in ejection and blast.Clinical RelevanceA new model needs to be developed to aid in the design of mine-protected vehicles for future conflicts.

Characterisation of explosive fragments injuring the neck

Penetrating explosive fragments are the most common cause of neck injuries sustained by UK service personnel deployed to Afghanistan. Analysis of these fragments will enable future ballistic protective materials to be tested with appropriate projectiles. However, only a small number of fragments excised from the neck have been available for analysis and they are potentially unrepresentative. We analysed computed tomograms (CTs) of 110 consecutive UK soldiers whose necks were wounded by explosive fragments. Fragments were classified according to shape, and their dimensions used to estimate volume and mass. These calculations were then compared with the actual measurements of the excised fragments using a general linear model. The 2 most common shapes were cylinders (52%) and spheres (21%). Known and estimated masses were not significantly different (p=0.64). A fragment-simulating projectile of 0.49 g represented 85% of fragments retained in the neck. CT can accurately delineate the shape and mass of fragments, which increases the number from which the most appropriate simulated projectile can be designed. We think that this methodology should be applied to fragments retained in other parts of the body to enable broader recommendations to be made regarding the testing of ballistic materials used to protect service personnel.

FASS is a better predictor of poor outcome in lower limb blast injury than AIS: implications for blast research.

Objectives Due to the absence of clinical blast data, automotive injury data using the abbreviated injury score (AIS) has been extrapolated to define current North Atlantic Treaty Organisation (NATO) injury thresholds for anti-vehicle mine tests. We hypothesized that AIS, being a marker of fatality rather than disability, would be a worse predictor of poor clinical outcome compared with the lower limb–specific foot and ankle severity score (FASS). Methods Using a prospectively collected trauma database, we identified UK Service Personnel sustaining lower leg injuries from under-vehicle explosions from January 2006 to December 2008. A full review of all medical documentation was performed to determine patient demographics and the severity of lower leg injury, as assessed by AIS and FASS. Clinical endpoints were defined as (1) need for amputation or (2) poor clinical outcome (defined as amputation or ongoing clinical problems). Statistical models were developed to explore the relationship between the scoring systems and clinical endpoints. Results Sixty-three UK casualties (89 limbs) were identified with a lower limb injury after under-vehicle explosion. The mean age of the casualty was 26.0 years. At 33.6 months follow-up, 29.1% (26 of 89) required an amputation and 74.6% (67 of 89) having a poor clinical outcome. Only 9 (14%) casualties were deemed medically fit to return to full military duty. Receiver operating characteristic analysis revealed that both AIS = 2 and FASS = 4 could predict the risk of amputation, with FASS = 4 demonstrating greater specificity (43% vs. 20%) and greater positive predictive value (72% vs. 34%). In predicting poor clinical outcome, FASS was significantly superior to AIS. Probit analysis revealed that a relationship could not be developed between AIS and the probability of a poor clinical outcome. Conclusions Our study clearly demonstrates that AIS is not a predictor of long-term clinical outcome and that FASS would be a better quantitative measure of lower limb injury severity.

Identifying spinal injury patterns in underbody blast to develop mechanistic hypotheses

Study Design. A retrospective case series of UK victims of blast injury. Objective. To identify the injury patterns in the spine caused by under-vehicle blast, and attempt to derive the mechanism of those injuries. Summary of Background Data. The Improvised Explosive Device has been a feature of recent conflicts with frequent attacks on vehicles, leading to devastating injuries. Vehicle design has evolved to reduce the risk of injury to occupants in underbody blast, where the device detonates beneath the vehicle. The mechanism of spinal injury in such attacks is not well understood; understanding the injury mechanism is necessary to produce evidence-based mitigation strategies. Methods. A Joint Theatre Trauma Registry search identified UK victims of blast between 2008 and 2013. Each victim had their initial scan reviewed to classify spinal fractures. Results. Seventy-eight victims were identified, of whom 53 were survivors. There were a total of 284 fractures, including 101 thoracolumbar vertebral body fractures and 39 cervical spine fractures. Most thoracolumbar fractures were wedge compression injuries. Most cervical spine fractures were compression-extension injuries. The most common thoracic and lumbar body fractures in this group suggest a flexed posture at the time of injury. Most cervical spine fractures were in extension, which might be compatible with the head having struck another object. Conclusion. Modifying the seated posture might reduce the risk of thoracolumbar injury, or allow the resulting injury patterns to be controlled. Cervical spine injuries might be mitigated by changing vehicle design to protect the head. Level of Evidence: N/A

Case suitability for definitive through knee amputation following lower extremity blast trauma: analysis of 146 combat casualties, 2008–2010

Introduction Analysis of recent UK Armed Forces combat casualty data has highlighted a significant number of through joint traumatic amputations (TAs), most commonly through knee (through knee amputations (TKAs)). Previously, a consensus statement on lower limb amputation from the UK Defence Medical Services reported better outcomes in some patients with TKAs when compared with those with above knee amputations. This study sought to define the proportion of recent combat casualties sustaining severe lower extremity trauma with acute osseous and soft tissue injury anatomy amenable to definitive TKA. Methods The UK Joint Theatre Trauma Registry and post mortem CT (PM-CT) databases were used to identify all UK Armed Forces personnel (survivors and fatalities) sustaining a major extremity TA (through/proximal to wrist or ankle joint) between August 2008 and August 2010. Through knee and all below knee TAs were grouped as ‘potential TKAs’ (pTKAs), that is, possible candidates for definitive TKA. Results 146 Cases (75 survivors and 71 fatalities) sustaining 271 TAs (130 in survivors, 141 in fatalities) were identified. The through-joint TA rate was 47/271 (17.3%); 34/47 through-joint injuries (72.3%) were TKAs. Overall, 63/130 TAs in survivors and 66/140 TAs in fatalities merited analysis as the pTKA group. Detailed anatomical data on pre-debridement osseous and soft tissue injury levels were only consistently available for fatalities through PM-CT findings. Further analysis of the soft tissue injury profile revealed that a definitive TKA in the pTKA group (all BKAs as well as TKAs) would have been proximal to the zone of injury (ZOI) in only 3/66 cases. Conclusions Traumatic TKAs following explosive blast are more common than previously reported. The majority of lower limb TAs are skeletally amenable to a definitive TKA. Maximising residual stump length carries the risks of definitive level amputation within the original ZOI but this study demonstrates that the proximal extent of the soft tissue injury may frequently make this unavoidable. Further work is required to determine the relative merits of definitive below, through and above knee amputations in the short, medium and long term to ensure survivors are subject to minimal complications while maintaining capacity to achieve optimal functional outcomes.

Computed Tomography Can Improve the Selection of Fragment Simulating Projectiles From Which to Test Future Body Armor Materials

INTRODUCTION Ballistic protective materials used in body armor are tested with fragment simulating projectiles (FSPs). The type of FSP used has historically been made by choosing fragments representative of those produced by controlled explosions, which may not be representative of those fragments actually injuring soldiers. METHOD 75 cylindrical FSPs of three different sizes were fired into six euthanized pigs, imaged using computed tomography (CT) and the wound tracks dissected. Skin entry wound locations, as determined by surface-shaded CT, were compared to clinical photographs. FSP dimensions and depth of penetration derived from CT were compared to surgical dissection using a Mann-Whitney U test. RESULTS Skin entry wound locations derived from CT were identical to that seen clinically. FSP dimensions were consistently 15% to 19% larger than the true measurements, reflecting the magnifying effect associated with metallic artifact. No statistical difference (p = 0.26) was found between depth of penetration measured radiologically compared to dissection when a projectile did not hit bone but there was a statistical difference when bone was hit (p < 0.05). CONCLUSIONS CT has the potential to accurately ascertain values required to improve the selection of representative FSPs from which future ballistic protective materials are tested.