Taking its toll: Troops on foot faced very different injuries to those in land vehicles (Photo: Crown Copyright) After 13 years of bloody conflict, British combat troops are gradually being withdraw from Afghanistan as responsibility for security is handed over to local forces. The military operation has taken a heavy toll: a total of 453 British service personnel had lost their lives when PE went to press.
In addition to these fatalities, more than 250 soldiers have been so severely injured that they have required major amputations. Many of these injuries were caused by improvised explosive devices (IEDs), which by their indiscriminate nature can cause trauma that is complex and highly variable.
Those caught by a bomb blast while on foot often suffered injuries very different to those seen in personnel who had ridden over an IED in a vehicle. Out in the open, the victim was often exposed to the full force of the primary blast-wave as well as secondary effects such as injury caused by flying debris and being thrown through the air. Inside an armoured personnel carrier, victims often escaped the primary blast-wave but suffered severe concussive injuries and other traumas caused by impact with the vehicle’s interior.
Indeed, such diverse scenarios, combined with improved battlefield treatment which ensured that many troops survived where previously they might have died, meant that a large number of soldiers came back from Afghanistan with types of injuries that many clinicians hadn’t seen before. According to Professor Anthony Bull, head of the Royal British Legion-sponsored Centre for Blast Injury Studies at Imperial College London, the conflict in Afghanistan changed the way that engineers and medical staff worked together to gain a better understanding of unusual blast conditions and the injuries they caused. “The conflict led to an urgent need to find ways of catering for a large cohort of wounded who were disabled in very different ways to people previously,” he says.
As the injuries in Afghanistan started to mount up, so the work at Imperial became more important. The centre brought together military and civilian clinicians with scientists and engineers to address specific clinical areas aimed at understanding blast injury mechanisms and investigating treatment and mitigation strategies. The facility grew in reputation to become widely regarded as one of the best of its kind in the world and unique in terms of the military-civilian cooperation.
Specific areas of expertise began to emerge, particularly in blast biomechanics, where engineers validate experimental and computational capability to test the effect of blast on the body. They use this to design and optimise mitigation strategies through personal protection, vehicle design and body position.
Another specialised area is blast-force protection, dealing with the interaction of the blast-wave with materials and structures around the human body.
“Our activities are wide and varied,” says Bull, whose own expertise is in biomechanics – how forces and motion are transmitted through the body. “We have developed a lot of experimental apparatus that is new and really rather unusual. In terms of how we carry out physical experiments, that is through the use of surrogates. It can be with crash-test dummies – we have worked on them to make them more realistic – or through the use of cadaver tissue. And then there are computational models.”
Impact assessment: Military vehicles offer protection against primary blast effects
The blast resistance of vehicles is a core area of research. The centre has developed its own test rig, the Anti-vehicle Underbelly Blast Injury Simulator (Anubis), to analyse the complex lower-limb injuries typically suffered by the occupants of armoured personnel carriers blown up by IEDs.
Anubis was designed to strict performance criteria and built by Newcastle company Northern Hydraulic Engineering. Comprising a heavy steel chassis mounted on wheels with high flotation tyres, the machine simulates the phenomenon of ‘deck-slap’ – the rapid acceleration of a solid floor propelled upwards by an explosion.
A frequent result of these incidents is a highly comminuted fracture of the calcaneus, the large heel-bone that bears most of the body’s weight. “This injury is highly specific and is almost unique to this kind of attack,” says Bull.
As well as using crash-test dummies as surrogates, the rig is designed to test the effects of deck-slap on actual human tissue, under regulated conditions.
Anubis achieves the appropriate acceleration by applying an upward force on a heavy steel plate mounted on a pressure vessel. The plate is held in place by a shear pin. The pressure inside the vessel is increased until the force applied to the plate shears the pin and the plate is propelled upwards.
The acceleration can be controlled accurately by selecting shear pins of varying materials and diameters. A 15mm steel pin, for example, will shear when pressure in the vessel reaches 30bar to produce acceleration of 16m/s2.
Bull says there was an urgent need to understand and mitigate deck-slap injuries. While the victims of this type of trauma may suffer no other lasting injury, the damage is so disabling and so difficult to treat that the long-term effects are disproportionately severe.
Bull describes seeing patients “who have no obvious outward injuries, but then you see this massive swelling of the foot and leg and when you investigate you see that the heel has been pulverised”. The damage, though highly localised, often never heals. Half of all patients sustaining this type of injury elect for amputation of the foot within a year.
Since commissioning Anubis in 2011, the centre has done hundreds of tests. The work has yielded information, published in scientific articles, which sheds light on the physics of this type of injury and how the occupants of armoured vehicles may be better protected.
One such paper describes an investigation into the positioning of passengers in the vehicle. It found that people seated with their feet flat on the floor suffered no fractures of the calcaneus from a typical detonation beneath the vehicle.
Those standing, however, suffered severe fractures, not just to the calcaneus but to other bones in the ankle and foot. Not surprisingly, this was because the entire body mass was impinging on the heel and pressing it into the floor, whereas seated passengers have only the weight of their legs resting on the foot. Also not surprising was the discovery that injuries were especially severe when the knee was in the locked position.
What was not expected was that when the knee was flexed by just 20º the injuries were no worse than when flexed at 90º in a seated position. While that seems logical, it was not immediately apparent before the tests were conducted.
A lot of people in the field thought that the worst injuries sustained in these attacks were inflicted on people being thrown from the vehicle by the blast. But the work of Bull and his team showed that most debilitating injuries were suffered by standing occupants in the vehicle. The solid blast effectively destroys the foot.
This knowledge, together with other data collected from tests at Imperial College, provided guidance for designers of military vehicles and protective equipment. This related to the positioning of passengers within vehicles, optimisation of posture, and protection from direct blast effects.
“We believe that it resulted in operational changes in the military,” says Bull. “It was an interesting example of where there has been clinical work, and physical and computational experiments, and then there’s been a change.
“We have also done some work optimising boot design, so that the optimum protection is provided to the most vulnerable parts of the foot and leg and even, if necessary, controlling and directing impacts to other parts of the leg where the resulting injuries are less severe and more easily treated. And we have recommended specific design of energy-absorbent floor mats for use in vehicles.
“We have been able to do that because we are the only organisation that can run physical experiments as we have the rigs set up to allow us to do so.”
The Anubis rig also provided useful indications of how modification to existing vehicles could help to mitigate the effects of deck-slap on the occupants. It is standard practice to design blast-resistant vehicles with a V-shaped hull to deflect the primary blast. It is the deformation of the interior floor surface that interests Imperial. The centre is investigating the interface between the hull and the floor, including the intervening space to see how deflection can be minimised.
Another interesting piece of work at Imperial has been research into the specific impact of a heavy explosion on the pelvis, a ring-like structure made up of a complicated girdle of bones.
Typically, in a car crash, fracture often occurs as the pelvis is pushed violently forwards, and clinical methods have been devised to treat that. But in Afghanistan, IED blasts were producing what Bull describes as a “gull-wing fracture”. This forced the pelvis to break in an upwards and outwards manner, and proved extremely difficult to treat.
“It was totally different to what we had seen before,” says Bull. “But based on our clinical data, with the application of some simple engineering sense, we found a better way to bring the pelvis back together and to bind it, which has resulted in increased survivability. It was an effective example of engineering at the interface with biologists and clinicians.”
Much of the research at the Centre for Blast Injury Studies has been driven by what was happening to troops in Afghanistan. But, with all British combat troops expected to have been withdrawn by the end of the year, it is hoped that the number of service personnel suffering IED injuries will sharply decline. That doesn’t mean that the work carried out by Bull and his team will come to an end: far from it, he says, as there is still much information to document so that further blast-related studies can be progressed.
“We need to continue learning from what’s happened. I say that because some of the information around the kinds of injuries that we saw people surviving in Afghanistan was probably known from the Second World War. But it wasn’t documented, so it wasn’t learnt.
“Although we are pulling out of Afghanistan, and we are not seeing the number of deaths and injuries that we were, we still need to capture learning. And there is a need to see how soldiers are doing in the long term – there needs to be more follow-up studies. So we will be increasingly involved in the rehabilitation and recovery side of things, pushing more into areas such as prosthetics design.”
Bull says the centre will “follow its nose” and go where the research takes it. One area that excites him is study into the formation of abnormal bone in muscle tissue following blast injury-related amputation. “We are looking at why this bone growth happens,” he says. “We have got experiments that look at how the bone cells are damaged but still stay alive, and therefore change what they do. They are really difficult experiments to set up.”
Prosthetics is another area of interest. “It’s the interface with the human – the biomechanics – that interests us,” he says. “If you have bone formation in the stump following amputation, then it can be extremely painful, stopping people from wearing their prosthesis. Understanding what is going on inside the stump affects the interface, and can result in a new design of socket or knee mechanism. It will be new information that will inform how other people work.”
Unfortunately, there are 500 explosions worldwide every month that cause serious injury to people, be it through landmines, terrorist actions or accidents. “It’s a major issue,” says Bull. “We have a unique facility here at the Centre for Blast Injury Studies. We are at the forefront of this effort on a worldwide stage.”
Danger zone: Imperial has carried out several studies on lower limb injuries
The devastating effects of bomb blasts
Casualties of IED explosions suffer very different injuries depending on whether they were mounted on or in a vehicle or were travelling on foot at the time.
A dismounted casualty will usually suffer traumatic amputation of one or more limbs in addition to more extensive primary and secondary blast injuries to other parts of the body.
A common complication is the effect of cavitation caused by rapidly expanding explosive gases and contamination of the resulting wounds by flying dirt and debris.
Mounted casualties tend to suffer different types of injury, although some primary blast effects are also likely.
Primary blast generally describes the sudden increase in air pressure created by the blast wave, which causes internal damage to air-containing organs. Pulmonary effects occur at pressures of 4.8bar. Exposure to pressures above 5.5bar is likely to prove fatal in 50% of cases.
Because the effects of blast decrease exponentially with distance, stand-off distance is an important factor, especially in vehicle design. By isolating the crew compartment and using deflectors to redirect the blast wave, occupants of military vehicles are much less likely to suffer primary blast effects than their dismounted colleagues.
Secondary, or solid, blast occurs when bomb fragments or nearby debris are energised by the explosion. This results in serious penetrating trauma. Vehicle occupants are at little risk of injury from anti-personnel mines, but are vulnerable to heavy objects, such as those produced by explosives designed to pierce armour plating.
As well as primary and secondary effects, injuries are often attributed to consequential damage:
Tertiary injuries are caused by the casualty being thrown by the explosion and colliding with solid objects. The term is also used to describe the effect of the impact caused by localised deformation of a vehicle floor – deck-slap injury.
Quaternary is used to describe the thermal effects of an explosion. Explosives generate temperatures of up to 6,000°C so severe burns are common. The term is also used to describe other risks, such as exposure to toxic substances or drowning, if a vehicle is blown into a river.
Quinary effects relate to subsequent illnesses caused by chemical, radiological or biological weapons.