Heterotopic ossification (HO) is perhaps the single most significant obstacle to independence, functional mobility, and return to duty for combat-injured veterans of Operation Enduring Freedom and Operation Iraqi Freedom. Recent research into the cause(s) of HO has been driven by a markedly higher prevalence seen in these wounded warriors than encountered in previous wars or following civilian trauma. To that end, research in both civilian and military laboratories continues to shed light onto the complex mechanisms behind HO formation, including systemic and wound specific factors, cell lineage, and neurogenic inflammation. Of particular interest, non-invasive in vivo testing using Raman spectroscopy may become a feasible modality for early detection, and a wound-specific model designed to detect the early gene transcript signatures associated with HO is being tested. Through a combined effort, the goals of early detection, risk stratification, and development of novel systemic and local prophylaxis may soon be attainable.

The conflict in Afghanistan has been epitomised by the emergence of the Improvised Explosive Device(IEDs). Improvements in medical treatments have resulted in increasing numbers of casualties surviving with complex lower extremity injuries. To date, there has been no analysis of foot and ankle blast injuries as a result of IEDs. Therefore the aims of this study are to firstly report the pattern of injury and secondly determine which factors were associated with a poor clinical outcome in order to focus future research. Using a prospective trauma registry, UK Service Personnel who sustained lower leg injuries following an under-vehicle explosion between Jan 2006 and Dec 2008 were identified. Patient demographics, injury severity, the nature of lower limb injury and clinical management was recorded. Clinical endpoints were determined by (i)need for amputation and (ii)need for ongoing clinical output at mean 33.0 months follow-up. 63 UK Service Personnel (89 injured limbs) were identified with lower leg injuries from explosion. 50% of casualties sustained multi-segmental injuries to the foot and ankle complex. 26(29%) limbs required amputation, with six amputated for chronic pain 18 months following injury. Regression analysis revealed that hindfoot injuries, open fractures and vascular injuries were independent predictors of amputation. Of the 69 limbs initially salvaged, the overall infection rate was 42%, osteomyelitis 11.6% and non-union rates was 21.7%. Symptomatic traumatic osteoarthritis was noted in 33.3% salvaged limbs. At final follow-up, 66(74%) of injured limbs had persisting symptoms related to their injury, with only 9(14%) fit to return to their pre-injury duties. This study demonstrates that foot and ankle injuries from IEDs are frequently associated with a high amputation rate and poor clinical outcome. Although, not life-threatening, they remain a source of long-term morbidity in an active population. Primary prevention of these injuries remain key in reducing the injury burden

Aims. In recent conflicts, most injuries to the limbs are due to blasts resulting in a large number of lower limb amputations. These lead to heterotopic ossification (HO), phantom limb pain (PLP), and functional deficit. The mechanism of blast loading produces a combined fracture and amputation. Therefore, to study these conditions, in vivo models that replicate this combined effect are required. The aim of this study is to develop a preclinical model of blast-induced lower limb amputation. Methods. Cadaveric Sprague-Dawley rats’ left hindlimbs were exposed to blast waves of 7 to 13 bar burst pressures and 7.76 ms to 12.68 ms positive duration using a shock tube. Radiographs and dissection were used to identify the injuries. Results. Higher burst pressures of 13 and 12 bar caused multiple fractures at the hip, and the right and left limbs. Lowering the pressure to 10 bar eliminated hip fractures; however, the remaining fractures were not isolated to the left limb. Further reducing the pressure to 9 bar resulted in the desired isolated fracture of the left tibia with a dramatic reduction in the fractures to other sites. Conclusion. In this paper, a rodent blast injury model has been developed in the hindlimb of cadaveric rats that combines the blast and fracture in one insult, necessitating amputation. Experimental setup with 9 bar burst pressure and 9.13 ms positive duration created a fracture at the tibia with total reduction in non-targeted fractures, rendering 9 bar burst pressure suitable for translation to a survivable model to investigate blast injury-associated diseases. Cite this article: Bone Joint Res 2021;10(3):166–173

A retrospective analysis of all paediatric patients admitted to Camp Bastion Role 3 between June 2006 and March 2013 was conducted from the UK trauma database. Patient demographics, mechanism of injury, anatomical distribution of injury and treatment are described. Two hundred and ninety eight children were admitted, 225 males with a median age of 9 years old. The highest number of cases (78) was recorded in 2011. Overall there were 55 fatalities (85.6% male). Most injuries were by IED (68% of cases) with 74% requiring operative intervention. Seventy-four percent of casualties had three or more anatomical regional injuries. Whilst the most commonly injured region was the lower limb (78%), head injuries were seen in 41%, abdominal injuries in 48% and thorax injuries in 44%. Debridement (including amputations) (59.4%) and laparotomy (30.6%) were the commonest operations performed. Sixty percent of cases were in theatre within one hour of arrival. Amongst survivors the mean ISS score was 17 and amongst fatalities 43; NISS 22 and 51; RTS 5.45 and 2.91. Paediatric blast injuries represent a significant burden to medical facilities in contemporary conflict. Whilst limb injuries predominate, the proportion of head and torso injuries is higher than seen in adult blast injuries

Purpose: Blast injury of the hand generally occurs during manipulations of unstable explosives. The explosion greatly damages the first commissure. The aim of this study was to define a classification system useful for establishing therapeutic strategy. Material and methods: From 1988 to 2002, we treated eight patients (nine hands, five dominant) with blast injury of the hand. Mean age was 24 years. Five hands were injured during manipulation of firecrackers and four during manipulation of munitions. The thumb was amputated on five hands, including three cases of index or medius amputation. Thumb revascularisation was successful in only one case. Two proximal thumb amputations were treated by twisted toe transfer. For one of these patients, the transfer was prepared by translocation of M2 on M1 using an inguinal flap. Two patients required a composite osteocutaneous reconstruction of M1 using the index as the bone source. In one final patient, lesions were limited to soft tissues. Discussion: Blast injured hands present several types of lesions: extensive soft tissue damage, diffuse vessel damage making revascularisation difficult or impossible, combined thenar and joint lesions leading to secondary closure of the first commissure. We distinguished three stages. Stage 1 involves only muscle and skin damage. After opening the first commissure with M1-M2 pinning, cover is achieved with a posterior interosseous flap or a skin graft. Stage 2 involves osteoarticular damage. Bone loss of M1 and P1 is often associated with dislocation. Bone reconstruction is often achieved using the distally amputated or greatly damaged thumb. Stage 3 involves amputation or devascularisation of the thumb. Reconstruction of the thumb is particularly difficult in these cases. If the amputation is distal beyond MP, M1 lengthening or classical toe transfer can be used. If the amputation is proximal, prior M1 reconstruction is required with a skin envelope using M2 fashioned with an interosseous or inguinal flap, followed by twisted toe transfer of the second toe. Stage 3 translocations are difficult because of the often damaged index and scar formation

The interaction of a blast wave with the thorax produces primary pulmonary blast injury by releasing energy at biological interfaces of differing acoustic impedance. This process is known as coupling. It was hypothesised that protective armour designed on the basis of an acoustic decoupler, may modulate the effect of thoracic blast. Anaesthetised, spontaneously breathing male pigs (n=18) were allocated into two equal groups and exposed to whole body blast in free field conditions. All animals were provided with Kevlar® protection, but in addition animals in group 2 were provided with protective thoracic armour. Blood gas analysis was performed prior to and up to 1 h post-blast. The animals were killed at 1 h post-blast and a post-mortem carried out. Severity of lung injury, called the quotient of injury (QI) was calculated by comparing masses of injured lung with standardised uninjured lung masses. All procedures complied with the Animals (Scientific Procedures) Act 1986. In group 1, PaO2 was reduced from a pre-blast mean of 9.7 kPa to a post-blast mean of 6.6 kPa, whereas in group 2 PaO2 fell from a pre-blast mean of 10.5 kPa to a post-blast mean of 8.3 kPa. The difference between the groups was statistically significant (p< 0.05). The mean QI in group 1 was 1.7 compared to a group 2 mean of 1.12, indicating severe injury in the unprotected animals (p< 0.01). Decoupling protective thoracic armour ameliorated the effects of thoracic blast in this animal model. This will lead to the development of personal protective thoracic armour for frontline servicemen

Conflict in Afghanistan demonstrated predominantly lower extremity and pelvi-perineal trauma secondary to Improvised Explosive Devices (IEDs). Mortality due to pelvic fracture (PF) is usually due to exsanguination. This study group comprised 169 military patients who sustained a PF and lower limb injury. There were 102 survivors and 67 fatalities (39% mortality). Frequent fracture patterns were a widened symphysis (61%) and widening of the sacroiliac joints (SIJ) (60%). Fatality was 20.7% for undisplaced SIJs, 24% for unilateral SIJ widening and 64% fatality where both SIJs were disrupted, demonstrating an increase in fatality rate with pelvic trauma severity. A closed pubic symphysis was associated with a 19.7% mortality rate versus 46% when widened. Vascular injury was present in 67% of fatalities, versus 45% of survivors. Of PFs, 84% were associated with traumatic amputation (TA) of the lower limb. Pelvic fracture with traumatic lower limb amputation presents a high mortality. It is likely that the mechanism of TA and PF are related, and flail of the lower limb(s) is the current hypothesis. This study prompts further work on the biomechanics of the pelvic-lower limb complex, to ascertain the mechanism of fracture. This could lead to evidence-based preventative techniques to decrease fatalities.

Introduction

A common injury pattern in current military experience is traumatic lower limb amputation from improvised explosive devices. This injury can co-exist with pelvic girdle fractures.

A common injury pattern in current military experience is traumatic lower limb amputation from improvised explosive devices. This injury can coexist with pelvic girdle fractures. Of 67 consecutive patients with traumatic lower limb amputations treated in Camp Bastion Hospital Afghanistan, 16 (24%) had an associated pelvic fracture (10 APC/vertical shear and 6 acetabular or pubic rami fractures). Traumatic single amputees (n=28) had a 14% incidence of associated pelvic fracture with traumatic double amputees (n=39) increasing this association to 31%. However if the double amputations were above knee the incidence of associated open book fractures was 26% (6/23) with 39% (9/23) sustaining some form of pelvic bony injury. The majority of patients (95%) had a pelvic X-ray as part of the primary survey. Of these 51% (n=34) had a Sam sling(r) in situ but only fifteen were deemed appropriately applied. Given the high risk of pelvic fractures in patients with traumatic bilateral lower limb amputations, particularly those involving opening of the pelvic ring, it is imperative that the earliest and proper application of a pelvic binder be initiated.

The defining weapon of the conflicts in Iraq and Afghanistan has been the Improvised Explosive Device (IEDs). When detonated under a vehicle, they result in significant axial loading to the lower limbs, resulting in devastating injuries. Due to the absence of clinical blast data, automotive injury data using the Abbreviated Injury Score (AIS) has been extrapolated to define current NATO injury thresholds for Anti-vehicle (AV) mine tests. We hypothesized that AIS, being a marker of fatality rather than disability would be a worse predictor of poor clinical outcome compared to the lower limb specific Foot and Ankle Severity Score (FASS).

Using a prospectively collected trauma database, we identified UK Service Personnel sustaining lower leg injuries from under-vehicle explosions from Jan 2006–Dec 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 (i) need for amputation or (ii) poor clinical outcome. Statistical models were developed in order to explore the relationship between the scoring systems and clinical endpoints.

63 UK casualties (89 limbs) were identified with a lower limb injury following under-vehicle explosion. The mean age of the casualty was 26.0 yrs. At 33.6 months follow-up, 29.1% (26/89) required an amputation and a further 74.6% (41/89) having a poor clinical outcome (amputation or ongoing clinical problems). Only 9(14%) casualties were deemed medically fit to return to full military duty. ROC 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 32%). In predicting poor clinical outcome, FASS was significantly superior to AIS (p<0.01). Probit analysis revealed that a relationship could not be developed between AIS and the probability of a poor clinical outcome (p=0.25).

Foot and ankle injuries following AV mine blast are associated with significant morbidity. 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. There is a requirement to reassess the current injury criteria used to evaluate the potential of mitigation technologies to help reduce long-term disability in military personnel. Our study highlights the critical importance of utilising contemporary battlefield injury data in order to ensure that the evaluation of mitigation measures is appropriate to the injury profile and their long-term effects.

The open blast fracture of the pelvis is considered to be the most severe injury within the spectrum of battlefield trauma. We report our experience of 29 consecutive patients who had sustained this injury in Afghanistan between 2008 and 2010. Their median new injury severity score (NISS) was 41 (8 to 75), and mean blood requirement in the first 24 hours was 60.3 units (0 to 224). In addition to their orthopaedic injury, six had an associated vascular injury, seven had a bowel injury, 11 had a genital injury and seven had a bladder injury. In all, eight fractures were managed definitively with external fixation and seven required internal fixation. Of those patients who underwent internal fixation, four required removal of metalwork for infection. Faecal diversion was performed in nine cases. The median length of hospital stay following emergency repatriation to the United Kingdom was 70.5 days (5 to 357) and the mean total operating time was 29.6 hours (5 to 187). At a mean follow-up of 20.3 months (13.2 to 29.9), 24 patients (82.8%) were able to walk and 26 (89.7%) had clinical and radiological evidence of stability of the pelvic ring.

As a result of the increase in terrorism, injuries that were previously confined exclusively to warfare can now occur anywhere, with civilian surgeons who are involved in trauma care potentially required to manage similar injuries. Our study demonstrates that the management of this injury pattern demands huge resources and significant multidisciplinary input. Given the nature of the soft-tissue injury, we would advocate external fixation as the preferred management of these fractures. With the advent of emerging wound and faecal management techniques, we do not believe that faecal diversion is necessary in all cases.

Spinal fractures are common following underbody blast. Most injuries occur at the thoracolumbar junction, and fracture patterns suggest the spine is flexed at the moment of injury. However, current mechanistic descriptions of vertebral fractures are based on low energy injuries, and there is no evidence to correlate fracture pattern with posture at the loading rates seen in blast injury. The T12-L1 segment of 4 human spines was dissected to preserve the paraspinal ligaments and potted in polymethylmecrylate. The specimens were impacted with a 14 kg mass at 3.5m/s in a drop tower; two specimens were impacted in neutral posture, one in flexion, and one in extension. A load cell measured the load history. CT scans and dissection identified the injury patterns. Each specimen sustained a burst fracture. The neutral specimens demonstrated superior burst fractures, the flexed specimen demonstrated a superior burst fracture with significant anterior involvement, and the extended specimen showed a posterior vertebral body burst fracture. At high loading rates, the posture of the spine at the moment of injury appears to affect the resulting fracture. This supports understanding the behaviour of the spine in blast injury and will allow improved mitigation system design in the future

Aims. Dystrophic calcification (DC) is the abnormal appearance of calcified deposits in degenerating tissue, often associated with injury. Extensive DC can lead to heterotopic ossification (HO), a pathological condition of ectopic bone formation. The highest rate of HO was found in combat-related blast injuries, a polytrauma condition with severe muscle injury. It has been noted that the incidence of HO significantly increased in the residual limbs of combat-injured patients if the final amputation was performed within the zone of injury compared to that which was proximal to the zone of injury. While aggressive limb salvage strategies may maximize the function of the residual limb, they may increase the possibility of retaining non-viable muscle tissue inside the body. In this study, we hypothesized that residual dead muscle tissue at the zone of injury could promote HO formation. Methods. We tested the hypothesis by investigating the cellular and molecular consequences of implanting devitalized muscle tissue into mouse muscle pouch in the presence of muscle injury induced by cardiotoxin. Results. Our findings showed that the presence of devitalized muscle tissue could cause a systemic decrease in circulating transforming growth factor-beta 1 (TGF-β1), which promoted DC formation following muscle injury. We further demonstrated that suppression of TGF-β signalling promoted DC in vivo, and potentiated osteogenic differentiation of muscle-derived stromal cells in vitro. Conclusion. Taken together, these findings suggest that TGF-β1 may play a protective role in dead muscle tissue-induced DC, which is relevant to understanding the pathogenesis of post-traumatic HO. Cite this article: Bone Joint Res 2020;9(11):742–750

Purpose: The purpose of this study is to evaluate the results of the treatment by severe blast injuries to limbs. Materials and methods: Twenty-seven patients after blast injuries were treated. There were 13 patients with tibial fractures, 7 fractures of the femur, 4 – fractures of the humerus and 3 with fractures of the forearm bones. According to Gustilo all fractures were open grade 3B and 3C. According to MESS a median value was 4,7 points (range 3 – 7). Six had on admission vascular injuries, and 12 had peripheral nerve injuries. There was other major organ trauma in 55,5% of patients. On admission, the fractured bones are realigned and stabilized with an AO tubular external fixation frame followed by immediate thorough soft tissue debridement, vascular reconstruction. In patients with peri-articular fractures temporary trans-articular bridging was needed. After 5 to 7 days or when wound condition permits, delayed primary sutures, the application of skin grafts or free tissue flaps are performed. At this stage, the tubular fixator is exchanged for a circular frame that allows stability, sufficient for full weight bearing by minimal invasive fixation and meticulous attention to freeing the previously bridged joints. Hybrid frames allows combination of advantages of each type of external fixators. Closed reduction of fractures was performed in most patients by ligamentotaxis and use thin wires with olives. Fixation in elastic frame combined with cyclic loading provide favorable biomechanical environment for fracture healing. In patients with high-energy “floating elbow” injuries the hybrid circular devices of the humerus and forearm were connected by hinges to allow immediate elbow joint movements. The separate fixation of the forearm bones was performed to allow early pronation/supination motions. Results: In all patients the external fixation was the definitive treatment. Fracture union was achieved at median time of 240 days (range 90 – 546). Throughout the period of fracture healing the patients were fully ambulatory, living at home. In three patients with bilateral highly complex blast injuries of lower extremities, where one limb had to be amputated, the Ilizarov device for severely injured contralateral limb provided the conditions necessary for early prosthetic fitting. There was one non-union and one patient developed chronic osteomyelitis treated by serial debridement and sequestrectomies. Conclusions: Based on this experience, we suggest that the stabilization in ring frame with radical debridement and early tissue transfer provides fracture healing and good functional results in extensive compound blast injuries of the extremities even in limbs categorized as high risk

The October 2012 Trauma Roundup. 360. looks at: which patients die from pelvic ring fractures; monolateral distraction osteogenesis; surgical management of pelvic and peroneal blast injuries; weekend warriors at risk of going AWOL; early experience with the locking attachment plate; and fibula nailing - an alternate, and viable technique

Introduction: Terrorist bombings, with catastrophic resultant blast injuries, have been increasing in frequency during past 25 years. Limbs injuries is common among survivors. Four crowded trains were attacked in Madrid on March 11, 2004. Injuries were sustained by 1550 people, 198 of whom died, mostly at the scene. Because the building station did not collapse, as in other attacks, the number of multiple injured patients who survive were high. 509 patients were attended at our Hospital in the emergency unit during the first six hours after the explosions, 80 of whom require hospitalization. Three patients died on arrival. Data about transport from the scene, injury type, diagnostic test and treatment and functional outcome were obtained from the Hospital Trauma Registry. The day at the Hospital:. The first patient arrived at 08:00, when the daily clinical meeting for the trauma admissions began. During the first hour, an effort was made in order to triage victims and organize the requirements for operating room and ICU treatment. All scheduled operations were aborted and six orthopaedic trauma teams were prepared to start operations immediately. A separate area in the Hospital was established to treat minor injuries. All patients were operated within the first 8 hours. Injury characteristics: 39 patients admitted with an ISS higher than 9 presented the most severe injuries. A study group was made with these patients. Mean age were 33,6. The mean RTS were 6,87, mean ISS 21,94, and mean NISS 26,15, revealing the high frequency of multisistemic injuries. The most frequently injury in these group were pulmonary blast injury, with a mean AIS for thorax of 2,7 points.74% of patients had some type of pulmonary blast injury. Limb injuries: 12 (25%) patients had open fractures, combined in all cases with pulmonary blast. Open Gustilo IIIb and IIIc occur in seven patients. Soft tissue injuries caused by small fragments were also frequent. Two patients presented SCIWORA like injuries of the thoracic medullary cord. All patients were operated in the first six hours after the explosion. A detailed description of the injuries, treatment and functional outcome will be presented. Functional outcome were analyzed by physical and psychological scales at six and twelve months after the attack. Scales used were SF-36(short form 36), EQ-5D (Euroqol), CES-D( Center for Epidemiologic Studies Depression Scale) and AVS. Comparison with a similar general trauma group revealed poorer functional outcome at six months for the study group. Conclusions: The bombing attack in Madrid was the first massive attack over civilian population in Europe since WW II. Functional outcomes were worse than expected in patients with skeletal injuries. In spite of the good results of initial treatment in our experience, we think that there is no country prepared sufficiently to treat this new type of massive casualties

The August 2012 Trauma Roundup. 360. looks at: pelvic fractures, thromboembolism and the Japanese; venous thromboembolism risk after pelvic and acetabular fractures; the displaced clavicular fracture; whether to use a nail or plate for the displaced fracture of the distal tibia; the dangers of snowboarding; how to predict the outcome of lower leg blast injuries; compressive external fixation for the displaced patellar fracture; broken hips in Morocco; and spinal trauma in mainland China

Following the invasion of Iraq in April 2003, Coalition forces have been conducting counter-insurgency operations in a bid to maintain security within the country. The improvised explosive device (IED) has become the weapon of choice of the terrorist and is the leading cause of death and injury amongst Coalition troops in the region. From Jan 2006, data was collected on 100 consecutive casualties who were either injured or killed during hostile action. Mechanism of injury, new Injury Severity Score (NISS), ICD-9 diagnosis and anatomical pattern of wounding was recorded in a trauma registry. During the study period, 53 casualties were injured by IEDs in 23 incidents (mean 2.3 casualties per incident). Twelve (22.6%) were killed or died of wounds. Mean NISS score of survivors was 5.4 (Range 1–50). There was no significant difference in NISS scores of survivors from fatal and non-fatal incidents. A mean 2.61 body regions were injured per casualty. Limb injuries were present in 45 (84.9%) of casualties, but primary blast injuries were seen in only 9 (14%). Twenty (48.7%) of survivors underwent surgery by British surgeons in the field hospital. Sixteen (39%) were deemed fit to return to duty after injury. IEDs used in Iraq do not follow the traditional pattern of injuries seen with conventional high explosives. Primary blast injuries were uncommon despite all casualties being in close proximity to the explosion. When the IED is detonated, an Explosive Formed Projectile (EFP) is formed which results in catastrophic injuries to casualties caught in its path, but causes relatively minor injuries to personnel sited adjacent to its trajectory. Enhanced vehicle protection may prevent the EFP from entering the passenger compartments and thereby reduce fatalities

Recent evidence suggests that both the accepted mechanism of blast-mediated traumatic amputation (TA) (shockwave then blast wind exposure) and the link with fatal shockwave exposure merit review. Searching UK military prospectively gathered trauma registry data and post mortem CT (PM-CT) records identified casualties from August 2008 to August 2010 with blast-mediated TAs. TA level and associated injuries were recorded. Data on pre-debridement osseous and soft tissue injuries were only consistently available for fatalities through PM-CT imaging. 146 Cases (75 survivors and 71 fatalities) with 271 TAs (130 in survivors and 141 in fatalities) were identified. Through-joint TA rate in fatalities was 34/141 (24.1%). PM-CT analysis demonstrated only 9/34 through joint TAs with contiguous fractures in the immediately proximal long bone/limb girdle. 18/34 had no fracture, and 7/34 had a non-contiguous fracture. The previously reported link between TA and blast lung injury was not present, calling into question the significance of shockwaves in generating blast-mediated TAs. Furthermore, contemporary blast injury theory cannot account for the high prevalence of through joint TAs (previously published rate 1.3%). The proportion of through joint TAs with no associated fracture or a non-contiguous fracture (74%) is supportive of pure flail as a mechanism for blast-mediated TA

The lower limbs of vehicle occupants are vulnerable to severe injuries during under vehicle explosions. Understanding the injury mechanism and causality of injury severity could aid in developing better protection. Therefore, we tested three different knee positions in standing occupants (standing, knee in hyper-extension, knee flexed at 20˚) of a simulated under‐vehicle explosion using cadaveric limbs in a traumatic blast injury simulator; the hypothesis was that occupant posture would affect injury severity. Skeletal injuries were minimal in the cadaveric limbs with the knees flexed at 20˚. Severe, impairing injuries were observed in the foot of standing and hyper‐extended specimens. Strain gauge measurements taken from the lateral calcaneus in the standing and hyper-extended positions were more than double the strain found in specimens with the knee flexed position. The results in this study demonstrate that a vehicle occupant whose posture incorporates knee flexion at the time of an under‐vehicle explosion is likely to reduce the severity of lower limb injuries, when compared to a knee extended position