An investigation into lower limb injuries caused by improvised explosive devices

The proliferation of Improvised Explosive Devices during the War in Afghanistan (2001 – 2014) caused many casualties and deaths on all sides of the conflict. Casualty data from the UK field hospital in Afghanistan identified 155 casualties with fractures in 108 femoral long bone segments in 93 femora, and 131 tibial long bone segments in 114 tibiae. The diaphysis was the commonest site of fracture in the tibia (53%) and femur (44%). The head and face (30%) and upper limbs (36%) were the commonest sites of associated injuries. A mechanism of injury analysis of these casualties found that only 3% had tympanic membrane ruptures and 1% had primary blast lung injury, which suggests a low likelihood of primary musculoskeletal blast injuries. There were only eight casualties with fractures caused by metallic fragments alone. Of the remaining casualties, 57 had an axial loading pattern of injuries, 46 had bending and torsional fractures, 15 had a mixed pattern and 29 could not be classified. Twenty-eight casualties with knee ligament injuries were identified, including 17 with tibio-femoral dislocations. These injuries were further characterised in a porcine stifle joint uniaxial tension model through strain rates in the range 0.01 to 100/s. Across the range of strain rates, tensile modulus increased from 288 to 905 MPa and tensile failure stress increased from 39.9 to 77.3 MPa. The strain rate sensitivity of the material properties decreased as deformation rates increased, and reached a limit at approximately 1/s, beyond which there was no further significant change. The effect of knee position on lower limb injury severity was investigated using a traumatic impact simulator capable of reproducing the axial impulse experienced by casualties mounted in vehicles during an IED attack. Cadaveric tests found that the severity of lower limb injuries was less severe when the knee was flexed at ~20 in a standing position.