Environment at the time of injury determines injury patterns in pelvic blast

Comparison of Adult Female and Male PMHS Pelvis and Lumbar Response to Underbody Blast

The goal of this study was to gather and compare kinematic response and injury data on both female and male whole-body Post-mortem Human Surrogates (PMHS) responses to Underbody Blast (UBB) loading. Midsized males (50th percentile, MM) have historically been most used in biomechanical testing and were the focus of the Warrior Injury Assessment Manikin (WIAMan) program, thus this population subgroup was selected to be the baseline for female comparison. Both small female (5th percentile, SF) and large female (75th percentile, LF) PMHS were included in the test series to attempt to discern whether differences between male and female responses were predominantly driven by sex or size. Eleven tests, using 20 whole-body PMHS, were conducted by the research team. Preparation of the rig and execution of the tests took place at the Aberdeen Proving Grounds (APG) in Aberdeen, MD. Two PMHS were used in each test. The Accelerative Loading Fixture (ALF) version 2, located at APG's Bear Point range was used for all male and female whole-body tests in this series. The ALF was an outdoor test rig that was driven by a buried explosive charge, to accelerate a platform holding two symmetrically mounted seats. The platform was designed as a large, rigid frame with a deformable center section that could be tuned to simulate the floor deformation of a vehicle during a UBB event. PMHS were restrained with a 5-point harness, common in military vehicle seats. Six-degree-of-freedom motion blocks were fixed to L3, the sacrum, and the left and right iliac wings. A three-degree-of freedom block was fixed to T12. Strain gages were placed on L4 and multiple locations on the pelvis. Accelerometers on the floor and seat of the ALF provided input data for each PMHS' feet and pelvis. Time histories and mean peak responses in z-axis acceleration were similar among the three PMHS groups in this body region. Injury outcomes were different and seemed to be influenced by both sex and size contributions. Small females incurred pelvis injuries in absence of lumbar injures. Midsized males had lumbar vertebral body fractures without pelvis injuries. And large females with injuries had both pelvis and lumbar VB fractures. This study provides evidence supporting the need for female biomechanical testing to generate female response and injury thresholds. Without the inclusion of female PMHS, the differences in the injury patterns between the small female and midsized male groups would not have been recognized. Standard scaling methods assume equivalent injury patterns between the experimental and scaled data. In this study, small female damage occurred in a different anatomical structure than for the midsized males. This is an important discovery for the development of anthropomorphic test devices, injury criteria, and injury mitigating technologies. The clear separation of small female damage results, in combination with seat speeds, suggest that the small female pelvis injury threshold in UBB events lies between 4 - 5 m/s seat speed. No inference can be made about the small female lumbar threshold, other than it is likely at higher speeds and/or over longer duration. Male lumbar spine damage occurred in both the higher- and lower lower-rate tests, indicating the injury threshold would be below the seat pulses tested in these experiments. Large females exhibited injury patterns that reflected both the small female and midsized male groups - with damaged PMHS having fractures in both pelvis and lumbar, and in both higher- and lower- rate tests. The difference in damage patterns between the sex and size groups should be considered in the development of injury mitigation strategies to protect across the full population.

Decreasing lower extremity junctional and perineal injury from explosive blast with a pelvic protection system

OBJECTIVE

Lower extremity junctional injuries due to explosive blasts are among the most lethal sustained on the battlefield. To help reduce the effects of junctional and perineal trauma from this injury mechanism, a tiered Pelvic Protection System (PPS) was fielded during the war in Afghanistan.

METHODS

Thirty-six patients with known PPS status who sustained traumatic above knee amputations, with and without perineal injuries, were identified from an operative amputation registry in Helmand Province, Afghanistan, spanning a 12-month period.

RESULTS

In Group 1 patients with above knee amputations who wore some tier of the PPS system, 47% (8 of 17) sustained junctional/perineal injuries. Of the patients in Group 2 who wore no PPS, 68% (13 of 19) sustained perineal injuries associated with proximal amputations. Overall, these differences were statistically significant (p = 0.0115).

CONCLUSION

Use of a PPS may reduce the risk of having severe perineal and lower extremity junctional injury in service members sustaining traumatic above knee amputations from an explosive blast.

Military experience in the management of pelvic fractures from OIF/OEF

INTRODUCTION

Pelvic fractures are a common occurrence in combat trauma. However, the fracture pattern and management within the most recent conflicts, i.e. Operation Enduring Freedom (OEF) and Operation Iraqi Freedom (OIF), have yet to be described, especially in the context of dismounted complex blast injury. Our goal was to identify the incidence, patterns of injury and management of pelvic fractures.

METHODS

We conducted a retrospective review on all combat-injured patients who arrived at our military treatment hospital between November 2010 and November 2012. Basic demographics, Young-Burgess fracture pattern classification and treatment strategies were examined.

RESULTS

Of 562 patients identified within the study time period, 14% (81 of 562) were found to have a pelvic fracture. The vast majority (85%) were secondary to an improvised explosive device. The average Injury Severity Score for patients with pelvic fracture was 31±12 and 70% were classified as open. Of the 228 patients with any traumatic lower extremity amputation, 23% had pelvic fractures, while 30% of patients with bilateral above-knee amputations also sustained a pelvic fracture. The most common Young-Burgess injury pattern was anteroposterior compression (APC) (57%), followed by lateral compression (LC) (36%) and vertical shear (VS) (7%). Only 2% (nine of 562) of all patients were recorded as having pelvic binders placed in the prehospital setting. 49% of patients with pelvic fracture required procedural therapy, the most common of which was placement of a pelvic external fixator (34 of 40; 85%), followed by preperitoneal packing (16 of 40; 40%) and angioembolisation (three of 40; 0.75%). 17 (42.5%) patients required combinations of these three treatment modalities, the majority of which were a combination of external fixator and preperitoneal packing. The likelihood to need procedural therapy was impacted by injury pattern, as 72% of patients with an APC injury, 100% of patients with a VS injury and 25% of patients with an LC injury required procedural therapy.

CONCLUSIONS

Pelvic fractures were common concomitant injuries following blast-induced traumatic lower extremity amputations. APC was the most common pelvic fracture pattern identified. While procedural therapy was frequent, the majority of patients underwent conservative therapy. However, placement of an external fixator was the most frequently used modality. Considering angioembolisation was used in less than 1% of cases, in the forward deployed military environment, management should focus on pelvic external fixation±preperitoneal packing. Finally, prehospital pelvic binder application may be an area for further process improvement.

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.

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.

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.