Influence of energy absorbers on Malgaigne fracture mechanism in lumbar-pelvic system under vertical impact load

Malgaigne fractures are the most common and widespread pelvic injuries resulting from the shear forces the action mechanism of which has not been explained in the literature yet. Military accidents with improvised explosive devices (IED) perfectly reflect this type of pelvic fracture. The finite element (FE) model of lumbar-pelvic complex (LPC) was developed based on computed tomography (CT) scans with the seat including steel frame, padding and soft tissue. The correlation coefficients of both low (100 N) and high (500 N) loads were greater than that currently obtained in the literature due to the presence of muscle force, pubic symphysis and joint cartilage. The dynamic analysis was performed to determine the influence of varying kinds of foam materials i.e. polyurethane, aluminium honeycomb structured and polyurethane auxetic foam on the stress/strain distribution in LPC under vertical impact load with the velocity of 7 m/s. Performed analysis showed the first fracture occurred in the L5 vertebrae resulting in the sacroiliac ligaments disruption and stress concentration in the pelvic ring causing further fractures of the wing of ilium, pubis and ischium bones. This results clearly explain the inconclusive findings about the second fracture that occurs in the pelvic area under a vertical impact load. The applied seat padding foam significantly reduced the stresses transmitted to the anatomical structures, thereby avoiding the risk of pelvic fracture. The analysis has proven that the auxetic polyurethane foam can be used as a good energy absorber.