Micromotion and Push-Out Evaluation of an Additive Manufactured Implant for Above-the-Knee Amputees.

In comparison to through-knee amputees the outcomes for above-the-knee amputees are relatively poor; based on this novel techniques have been developed. Most current percutaneous implant-based solutions for transfemoral amputees make use of high stiffness intramedullary rods for skeletal fixation, which can have risks including infection, femoral fractures, and bone resorption due to stress shielding. This work details the cadaveric testing of a short, cortical bone stiffness-matched subcutaneous implant, produced using additive manufacture, to determine bone implant micromotion and push-out load. The results for the micromotions were all <20 µm and the mean push-out load was 2,099 Newtons. In comparison to a solid control, the stiffness-matched implant exhibited significantly higher micromotion distributions and no significant difference in terms of push-out load. These results suggest that, for the stiffness-matched implant at time zero, osseointegration would be facilitated and that the implant would be securely anchored. For these metrics, this provides justification for the use of a short-stem implant for transfemoral amputees in this subcutaneous application. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 37:2104-2111, 2019.

Fatal head and neck injuries in military underbody blast casualties.

INTRODUCTION: Death as a consequence of underbody blast (UBB) can most commonly be attributed to central nervous system injury. UBB may be considered a form of tertiary blast injury but is at a higher rate and somewhat more predictable than injury caused by more classical forms of tertiary injury. Recent studies have focused on the transmission of axial load through the cervical spine with clinically relevant injury caused by resultant compression and flexion. This paper seeks to clarify the pattern of head and neck injuries in fatal UBB incidents using a pragmatic anatomical classification. METHODS: This retrospective study investigated fatal UBB incidents in UK triservice members during recent operations in Afghanistan and Iraq. Head and neck injuries were classified by anatomical site into: skull vault fractures, parenchymal brain injuries, base of skull fractures, brain stem injuries and cervical spine fractures. Incidence of all injuries and of each injury type in isolation was compared. RESULTS: 129 fatalities as a consequence of UBB were identified of whom 94 sustained head or neck injuries. 87 casualties had injuries amenable to analysis. Parenchymal brain injuries (75%) occurred most commonly followed by skull vault (55%) and base of skull fractures (32%). Cervical spine fractures occurred in only 18% of casualties. 62% of casualties had multiple sites of injury with only one casualty sustaining an isolated cervical spine fracture. CONCLUSION: Improvement of UBB survivability requires the understanding of fatal injury mechanisms. Although previous biomechanical studies have concentrated on the effect of axial load transmission and resultant injury to the cervical spine, our work demonstrates that cervical spine injuries are of limited clinical relevance for UBB survivability and that research should focus on severe brain injury secondary to direct head impact.

Characterization of Lower Extremity Blast Injury.

BACKGROUND: Throughout history, traumatic amputation of the lower extremity has been a notable feature of all conflicts involving explosive incidents. Even at the close of the recent conflicts in Afghanistan, there were deaths that were deemed "potentially survivable." The purpose of this study is to characterize lower extremity blast injury and to determine if their amputation levels and associated injury characteristics correlate with a higher risk of mortality. METHODS: the UK Joint Theatre Trauma Registry (JTTR) was interrogated to identify all lower extremity traumatic amputations sustained in both Iraq and Afghanistan between January 2003 and the end of UK operations in August 2014. The mortality rates for each amputation level and associated injuries were determined. FINDINGS: Of the 977 casualties, there were 679 (69.5%) survivors and 298 fatalities (30.5%). There was an increase in survivability from traumatic amputation throughout the conflict, however, traumatic amputations at the close of military activity in 2014 still had a substantial fatality rate of 23%. A more proximal level of amputation, an associated pelvic fracture, and an associated abdominal injury all correlated with an increased mortality rate. DISCUSSION: Several specific injury characteristics associated with traumatic amputation have been identified that are associated with an increased mortality rate to include a more proximal amputation level, pelvic fracture, and abdominal injury. Injury prevention and mitigation measures should be explored to minimize the risk of the associated injuries following blast that portend a higher risk of mortality.

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.

Defining the essential anatomical coverage provided by military body armour against high energy projectiles.

INTRODUCTION: Body armour is a type of equipment worn by military personnel that aims to prevent or reduce the damage caused by ballistic projectiles to structures within the thorax and abdomen. Such injuries remain the leading cause of potentially survivable deaths on the modern battlefield. Recent developments in computer modelling in conjunction with a programme to procure the next generation of UK military body armour has provided the impetus to re-evaluate the optimal anatomical coverage provided by military body armour against high energy projectiles. METHODS: A systematic review of the literature was undertaken to identify those anatomical structures within the thorax and abdomen that if damaged were highly likely to result in death or significant long-term morbidity. These structures were superimposed upon two designs of ceramic plate used within representative body armour systems using a computerised representation of human anatomy. RESULTS AND CONCLUSIONS: Those structures requiring essential medical coverage by a plate were demonstrated to be the heart, great vessels, liver and spleen. For the 50th centile male anthropometric model used in this study, the front and rear plates from the Enhanced Combat Body Armour system only provide limited coverage, but do fulfil their original requirement. The plates from the current Mark 4a OSPREY system cover all of the structures identified in this study as requiring coverage except for the abdominal sections of the aorta and inferior vena cava. Further work on sizing of plates is recommended due to its potential to optimise essential medical coverage.

Effectiveness of the combat pelvic protection system in the prevention of genital and urinary tract injuries: An observational study.

BACKGROUND: Historically, the incidence of genital and urinary tract (GU) injuries in major conflicts has been approximately 5%. To mitigate the risk of blast injury to the external genitalia, the United States and United Kingdom issued protective overgarments and undergarments to troops deployed in support of Operation Enduring Freedom. These two systems combined constitute the pelvic protection system (PPS). Our hypothesis was that PPS use is associated with a reduction of GU injuries in subjects exposed to dismounted improvised explosive device blast injuries. METHODS: We identified two groups for comparison: those who were confirmed to have worn the PPS at time of injury (n = 58) and a historical control group who were confirmed as not wearing the PPS (non-PPS) (n = 61). Patients with any level of lower extremity amputation from dismounted improvised explosive device blast mechanism were included. The primary outcome measure was presence of a GU injury on admission. A univariate analysis assessing the strength of association with odds ratios and 95% confidence intervals was performed between the PPS and non-PPS groups. RESULTS: Mean Injury Severity Score (ISS) was higher in the PPS versus the non-PPS group (26.1 vs. 19.3, p = 0.0012). Overall, 31% of the patients in the PPS group sustained at least one GU injury versus 62.3% in the non-PPS group. The odds ratio of sustaining a GU injury in the PPS group as compared with the PPS group is 0.28 (31% vs. 62.3%; 95 % confidence interval, 0.62-0.12; p < 0.001). The most frequent injures were open scrotal/testes wounds, followed by open penis, and open bladder/urethra injuries. CONCLUSION: The use of the PPS is associated with a decreased odds ratio of GU injury. Despite a 31% absolute reduction, future work should focus on improved efficiency. LEVEL OF EVIDENCE: Prognostic/epidemiologic study, level IV; therapeutic study, level V.

What Is the Magnitude and Long-term Economic Cost of Care of the British Military Afghanistan Amputee Cohort?

BACKGROUND: Personal protection equipment, improved early medical care, and rapid extraction of the casualty have resulted in more injured service members who served in Afghanistan surviving after severe military trauma. Many of those who survive the initial trauma are faced with complex wounds such as multiple amputations. Although costs of care can be high, they have not been well quantified before. This is required to budget for the needs of the injured beyond their service in the armed forces. QUESTION/PURPOSES: The purposes of this study were (1) to quantify and describe the extent and nature of traumatic amputations of British service personnel from Afghanistan; and (2) to calculate an estimate of the projected long-term cost of this cohort. METHODS: A four-stage methodology was used: (1) systematic literature search of previous studies of amputee care cost; (2) retrospective analysis of the UK Joint Theatre Trauma and prosthetic database; (3) Markov economic algorithm for healthcare cost and sensitivity analysis of results; and (4) statistical cost comparison between our cohort and the identified literature. RESULTS: From 2003 to 2014, 265 casualties sustained 416 amputations. The average number of limbs lost per casualty was 1.6. The most common type of amputation was a transfemoral amputation (153 patients); the next most common amputation type was unilateral transtibial (143 patients). Using a Markov model of healthcare economics, it is estimated that the total 40-year cost of the UK Afghanistan lower limb amputee cohort is £288 million (USD 444 million); this figure estimates cost of trauma care, rehabilitation, and prosthetic costs. A sensitivity analysis on our model demonstrated a potential ± 6.19% variation in costs. CONCLUSIONS: The conflict in Afghanistan resulted in high numbers of complex injuries. Our findings suggest that a long-term facility to budget for veterans' health care is necessary. CLINICAL RELEVANCE: Estimates here should be taken as the start of a challenge to develop sustained rehabilitation and recovery funding and provision.

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

BACKGROUND: Improvised 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/PURPOSES: We 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. METHODS: UK 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. RESULTS: The 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. CONCLUSIONS: The 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 RELEVANCE: A new model needs to be developed to aid in the design of mine-protected vehicles for future conflicts.

Ergonomic assessment of future methods of ballistic neck protection.

INTRODUCTION: Neck injuries from explosively propelled fragments are present in 11% of injured U.K. soldiers and result in significant mortality and long-term morbidity. U.S. forces in contrast sustain only neck wounds in 3 to 4% of those injured, which is believed to be because of their greater acceptance in the wearing of issued neck protection. METHOD: A three-piece neck collar, two-piece neck collar, a nape pad, a ballistic scarf, and an enhanced protection under body armor shirt (EP-UBACS) reinforced at the collar were objectively compared during a treadmill test using physiological measurements. Designs were subjectively compared regarding their effect on soldier performance using representative military tasks. RESULTS: Both neck collars and the EP-UBACS prototype demonstrated 90% acceptability in terms of military task performance. No statistical difference in tympanic temperature and heart rate was found between prototypes. The statistically significant higher skin temperatures found for prototypes lying close to the skin (EP-UBACS and ballistic scarf) were unrelated to perceived comfort. DISCUSSION: Neck collars remain the most successful design in terms of military performance, comfort, and potential levels of ballistic protection. However the EP-UBACS concept should also be developed further, with future iterations potentially removing the zip and increasing skin standoff.

Use and complications of operative control of arterial inflow in combat casualties with traumatic lower-extremity amputations caused by improvised explosive devices.

BACKGROUND: Proximal traumatic lower-extremity amputation has become the signature injury of the war in Afghanistan. Casualties present in extremis and often require immediate operative control of arterial inflow to prevent exsanguination. This study evaluated the use of this strategy and its complications. METHODS: This is a retrospective analysis of case notes of UK service personnel, identified from the UK Joint Theatre Trauma Registry, who sustained traumatic lower-extremity amputation requiring suprainguinal vascular control, following improvised explosive device injury in Afghanistan, between July 2008 and December 2010. RESULTS: Fifty-one casualties were identified with a median Injury Severity Score (ISS) of 30. In 10 casualties, control was obtained via an extraperitoneal approach, and in 41, control was obtained via midline laparotomy and intraperitoneal (IP) approach. The most commonly controlled vessel in extraperitoneal control was the external iliac artery, and in IP control, the common iliac artery. Within the 41 patients who had IP control, 13 also required a therapeutic laparotomy, and 9 patients had bilateral injuries at the level of the proximal femur or higher. One patient, who had undergone IP control, experienced an injury to the common iliac vein, which was repaired. There were no other immediate complications recorded, and 39 casualties survived to discharge. CONCLUSION: This is the first study to characterize the methods of proximal control in high wartime lower-extremity amputees. Although some casualties will have abdominal injuries that necessitate laparotomy, the majority in our study did not; however, in the critically ill casualty, rapid proximal control is required. Novel methods of temporary hemorrhage control may reduce the need for, and burden of, cavity surgery. LEVEL OF EVIDENCE: Epidemiologic study, level III; prognostic study, level IV.

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.

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.

Design of a traumatic injury simulator for assessing lower limb response to high loading rates.

Current military conflicts are characterized by the use of the improvised explosive device. Improvements in personal protection, medical care, and evacuation logistics have resulted in increasing numbers of casualties surviving with complex musculoskeletal injuries, often leading to life-long disability. Thus, there exists an urgent requirement to investigate the mechanism of extremity injury caused by these devices in order to develop mitigation strategies. In addition, the wounds of war are no longer restricted to the battlefield; similar injuries can be witnessed in civilian centers following a terrorist attack. Key to understanding such mechanisms of injury is the ability to deconstruct the complexities of an explosive event into a controlled, laboratory-based environment. In this article, a traumatic injury simulator, designed to recreate in the laboratory the impulse that is transferred to the lower extremity from an anti-vehicle explosion, is presented and characterized experimentally and numerically. Tests with instrumented cadaveric limbs were then conducted to assess the simulator's ability to interact with the human in two mounting conditions, simulating typical seated and standing vehicle passengers. This experimental device will now allow us to (a) gain comprehensive understanding of the load-transfer mechanisms through the lower limb, (b) characterize the dissipating capacity of mitigation technologies, and (c) assess the bio-fidelity of surrogates.

Outcomes of IED foot and ankle blast injuries.

BACKGROUND: Improvements in protection and medical treatments have resulted in increasing numbers of modern-warfare casualties surviving with complex lower-extremity injuries. To our knowledge, there has been no prior analysis of foot and ankle blast injuries as a result of improvised explosive devices (IEDs). The aims of this study were to report the pattern of injury and determine which factors are associated with a poor clinical outcome. METHODS: U.K. service personnel who had sustained lower leg injuries following an under-vehicle explosion from January 2006 to December 2008 were identified with the use of a prospective trauma registry. Patient demographics, injury severity, the nature of the lower leg injury, and the type of clinical management were recorded. Clinical end points were determined by (1) the need for amputation and (2) ongoing clinical symptoms. RESULTS: Sixty-three U.K. service personnel (eighty-nine injured limbs) with lower leg injuries from an explosion were identified. Fifty-one percent of the casualties sustained multisegmental injuries to the foot and ankle. Twenty-six legs (29%) required amputation, with six of them amputated because of chronic pain eighteen months following injury. Regression analysis revealed that hindfoot injuries, open fractures, and vascular injuries were independent predictors of amputation. At the time of final follow-up, sixty-six (74%) of the injured limbs had persisting symptoms related to the injury, and only nine (14%) of the service members were fit to return to their preinjury duties. CONCLUSIONS: This study demonstrates that foot and ankle injuries from IEDs are associated with a high amputation rate and frequently with a poor clinical outcome. Although not life-threatening, they remain a source of long-term morbidity in an active population.

Traumatic amputations.

Traumatic amputations remain one of the most emotionally disturbing wounds of conflict, as demonstrated by their frequent use in films to illustrate the horrors of war. Unfortunately, they remain common injuries, particularly following explosions, and, in addition, many survivors require primary amputation for unsalvageable injuries or to save their life. A third group, late amputations, is being increasingly recognised, often as a result of the sequelae of complex foot injuries. This article will look at the epidemiology of these injuries and their acute management, complications and outcome.

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.

The development of an experimental model of contaminated muscle injury in rabbits.

Extent of tissue trauma and contamination determine outcome in extremity injury. In contrast to fracture, osteomyelitis, and closed muscle injury studies, there are limited small animal models of extremity muscle trauma and contamination. To address this we developed a model of contaminated muscle injury in rabbits. Twenty-eight anesthetized New Zealand White rabbits underwent open controlled injury of the flexor carpi ulnaris (FCU). Twenty-two animals had subsequent contamination of the injured muscle with Staphylococcus aureus. All animals were sacrificed at 48 hours and the level of muscle injury and contamination determined by quantitative histological and microbiological analysis. A 1-kg mass dropped 300 mm onto the mobilized FCU resulted in localized necrosis of the muscle belly. Delivery of a mean challenge of 3.71 × 10(6) cfu/100 µL S aureus by droplet spread onto the injured muscle produced a muscle contamination of 8.79 × 10(6) cfu/g at 48 hours. Ipsilateral axillary lymph nodes demonstrated clinically significant activation. All animals had normal body temperature and hematological parameters throughout and blood and urinalysis culture at autopsy were negative for organisms. This model allows reproducible muscle injury and contamination with the organism ubiquitous to extremity wound infection at a level sufficient to allow quantitative assessment of subsequent wound care interventions without incurring systemic involvement.