Documentation:FIB book/Motorcycle Pelvic Injuries

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Background

Types of Pelvic Ring Injuries[1]

There are many types of injuries that can occur in motorcycle crashes. These vary depending on the method of the crash, the speed of the vehicle(s) involved, the seating position, and the occupant safety equipment used by the rider. However, injuries that cannot be controlled by the occupant are pelvic ring and associated soft tissue injuries caused by the positioning of the fuel tank. Pelvic ring injuries are a category of injuries that result in disruptions to the structure formed by the the sacrum and the two innominate bones, formed by one of each the ilium, ischium, and pubis[2]. The ring is not inherently stable and held together with ligamentous attachments, so stability of the ring depends on the strength of these ligaments.

Standard location of a motorcycle fuel tank

The fuel tank is positioned towards the front of the seat, between the legs of the occupant when the rider is seated correctly on a motorcycle. When the front brakes on a motorcycle are applied, or when the motorcycle is forcibly stopped by an impact, the rider will move forward due to momentum, moving them against the fuel tank. When the front brakes of the motorcycle are applied before an impact, it has been shown to reduce impact severity[3]. However, if the rider does not brake before an impact, as they often don't have enough time to react, the rider is propelled forward on the seat into the fuel tank. This collision between the rider's pelvis and fuel tank can cause a variety of injuries, such as damage to soft tissues around the pelvis, including the bladder, urethra, genitals, and prostate,[4] as well as high-energy impacting fractures to the pelvis, known as pelvic ring injury[5]. The ability of a rider to brake before collision is a function of their riding experience, age, and type of motorcycle ridden[6]. The severity of the pelvic injury is based on the amount of loading the pelvis experiences from the fuel tank, which is based on delta-V of the impact and the angle of the fuel tank (steeper angle, higher impacting force)[7][8].

Significance

In comparison to cars, motorcycles make up a significantly smaller proportion of motor vehicles on the road; accounting for only 3% of registered vehicles in the United States[9]. However, motorcycle riders account for 14% of all traffic fatalities and 18% of all occupant fatalities[9], which indicates that motorcycle occupants lack safety while on the road. According to various studies, approximately 13% of fatalities[10][11] resulting from motorcycle crashes can be linked back to pelvic ring injuries. Considering there were over 5500 motorcycle related deaths in 2020 in the United States[12], this percentage correlates to over 715 deaths resulting from pelvic ring injuries obtained in motorcycle crashes. This injury modality was identified in 1985[13], and continues to be a fatal problem for riders.

Summary of Previous Work

With the prevalence and severity of pelvic injuries in motorcycle crashes, the lack of research surrounding this topic limits the development of safety equipment and guidelines. The primary tools used in research on this topic have included anthropometric test devices (ATD’s), finite element models, epidemiological studies, and cadaver studies.

Anthropometric Test Devices

Rendition of the set up of the Whyte et al. study including the deceleration sled, pelvis surrogate and fuel tank.

A study by Whyte et al. aimed to construct an apparatus to simulate the impact between a motorcycle rider and the fuel tank during a crash scenario[14]. Deceleration sled testing was performed using a surrogate consisting of the THOR ATD lumbar spine, pelvis, and upper leg components. As this ATD is designed for car testing, it was modified by updating the existing soft tissue to allow for the separation of the upper legs to have a more biofidelic motorcycle rider positioning. The pelvis surrogate was designed to be able to rotate in the sagittal plane and translate vertically. The lumbar spine of the surrogate was instrumented with two triaxial accelerometers and the event was captured using high-speed cameras.

Sled testing was performed using an impact speed of 18 kph. Four fuel tank shapes (two sport-style motorcycle - one metal and one plastic with a plastic cover, one metal from a standard motorcycle, and one metal form a cruiser motorcycle) and seven pelvis protector inserts of varying materials were tested. The multiple fuel tank shapes and models were used due to the wide range of motorcycle styles available on the market, with varying fuel tank shapes and materials. Acceleration was used to quantify injury of the pelvis because the acceleration of the center of mass of a body during impact can be used to quantify impact severity[15]. As the study was using acceleration as the primary metric for impact severity, they aimed to determine how different materials of pelvis protector inserts and different fuel tank angles and materials could reduce pelvis accelerations. While the study did find lower accelerations for certain inserts (0-20g's), they emphasized that the lack of injury tolerance data of this body region limits the assumptions that can be made based on the results. The results of this study show promise in the ability to test and improve pelvis-specific motorcycle related safety equipment.

Finite Element Modelling

A study by Breaud et al. investigated whether the severity of pelvic ring fracture could predict the risk of posterior urethral injury in motorcycle-car crashes involving male adolescent riders[4]. A finite element model of the pelvis and anterior perineum developed by reconstructing 3D anatomical images of the pelvic region of a healthy 15 year old male. The material properties of the bony (cortical and cancellous bone), muscular, and ligamentous structures were determined using existing biomechanical data. The risk of posterior urethral injury was determined by measuring the amount of tissue deformation of the posterior urethra with respect to time, while failure of the pelvis was determined by measuring the distance between the middle of the prostatic urethra and the membranous urethra.

The model was applied in three common impact scenarios: 1) lateral trauma: impacting the acetabulum by a 3.6 kg cylinder at 4 m/s speed, 2) antero-posterior trauma: impacting the symphysis pubis by a rigid plaque at 1 m/s speed, and 3) motorcycle-car crash: motorcycle crashing into a car door from behind at 50 km/h at an angle of 45°. In the lateral impact, fracture of the two ilio- and ischio-pubic rami, and in the antero-posterior impact, fracture of the ischial and ilial pubic rami occured. In all three scenarios, the junction between the prostatic and membranous urethra experienced deformations between 1.5 and 2 mm before bone failure occurred [4]. This study can guide future research on whether such stretching values can potentially lead to severe ruptures and dislocation of the prostate.

Epidemiological Studies

Various existing studies have aimed to identify the epidemiology of pelvic injuries in motorcycle crashes through the study of the mechanisms and types of pelvic injuries associated with such crashes.

A study conducted by Meredith et al. reviewed data from two varieties of in-depth crash investigations to identify the mechanisms by which pelvic injuries occurred in motorcycle crashes, as well as to determine the types of pelvic injuries experienced[7]. The available data was filtered to include only crashes in which riders obtained pelvic injuries. The study found that direct contact between the pelvis and the fuel tank was the most prevalent cause of pelvic injury in motorcycle crashes, accounting for 85% of injuries to the pelvis. Such injuries were found to differ from pelvic injuries caused by other mechanisms both in terms of the asymmetry of loading to the pelvis as well as the degree of injury to the bladder. Furthermore, it was determined that the types of injuries which resulted from pelvic contact with the fuel tank could be grouped into three distinct categories based on injury complexity and type: 1) bladder and/or soft tissue injuries only, 2) fracture to the anterior pelvis, and 3) fracture to the anterior and posterior portions of the pelvis.

Similarly, a review of common mechanisms of injury in motorcycle collisions by Petit et al. further concludes that fuel tank injuries are attributable to a direct impact between the pelvis and fuel tank, and can thereby be categorized as having a collision injury mechanism[16]. Fuel tank injuries have been shown to occur due to the inertia experienced by the body of the rider when the motorcycle comes to a sudden stop, resulting in the rider being propelled forward on the motorcycle. This mechanism often results in the impact between the pelvis and the fuel tanks occurring at high peak loads. It was further noted in this review that higher levels of injury experienced as a result of these mechanisms, such as those denoted as injury types 2) and 3) by Meredith et al., are suggestive of higher velocities at the time of impact. Epidemiological studies, such as those noted here, have furthered scientific understanding of the mechanism of fuel tank injury, as well as the types of injuries sustained as a result of such mechanisms. By identifying and classifying how, and to what extent, motorcycle fuel tanks contribute to pelvic injuries, the design of motorcycles, restraints, or protective equipment can be better informed in the future.

Cadaver Study

A study by Serre et al. used cadaveric impact studies to examine collisions between a motorcyclist and a lightweight vehicle[17].  Full scale crash tests following ISO 132232[18] were performed wherein the motorcycle impacts the side of the vehicle head-on at a speed of 40 kph. This was done using cadaveric full body surrogates which were instrumented with triaxial accelerometers on their head, left and right 4th and 8th rib, and cervical spine (C5). While the pelvis was not instrumented in this study, pelvic fractures were observed in this loading scenario, likely due to impact with the gas tank. The severity of these fractures was not discussed. Due to the limited results of this study, it can only be concluded that pelvic fractures can occur during motorcycle crashes but further research must be done to quantify injury tolerances and specific loading conditions.

Problems and Controversies

Age and sex of riders are the two characteristics which are underexplored in the current research in terms of their effect on biomechanical risk and methods of risk reduction for motorcycle occupants. Age is noted as one of the main contributors to pelvic ring injury risk, with the risk of pelvic injury increasing by 3% for each additional year of age of the rider[7]. Since musculoskeletal stability decreases with age[19], testing that utilizes the 50th percentile male as a standard does not reflect the risks facing older populations in terms of obtaining an injury. Similarly, testing utilizing male subjects does not reflect the risks facing female populations considering the sexual dimorphism of the human pelvis anatomy[20]. While males more often receive fatal pelvic injuries (7.8% of male riders had fatal pelvic fractures vs 2.9% of female riders), women tend to receive more pelvic injuries as a whole (3.0% of male riders had pelvic fractures vs 4.2% of women), indicating that there is significant basis for research to be done[7][21].

Future Research

Protective Clothing

The use of protective clothing has been essential for mitigating motorcycle injuries. Studies by de Rome et al. reported that motorcyclists who wore protective clothing, including boots and motorcycle-specific jackets and pants, had a significantly lower probability of hospitalization[22]. For example, out of the group of patients considered by Rome et al., those who did not wear a motorcycle jacket had an injury rate of 91.9 %, whereas the rate of injury decreased to 69.9% for those wearing motorcycle-specific jackets featuring body armor [22]. Unfortunately, while motorcycle-specific pants do exist, current protective clothing designs do not include protection for the groin region[14]. The previously mentioned study conducted by Whyte et al. investigated the feasibility of region-specific protective clothing as a pelvic injury mitigation strategy[14]. This study found protective clothing to be a feasible avenue to explore, however, the study additionally determined that a better understanding of pelvic injury tolerance is required in order to create effective protective clothing for mitigation of pelvis injury. Thus, future work exploring the pelvic response under a load exerted by a fuel tank will be vital for the development of adequate protective clothing.

Cadaver Testing for Material Properties

Arguably, the best method to determine the pelvic response under loading is through the use of cadaver testing. While cadaver testing has been used in motorcycle collision research, as previously discussed, studies such as the one performed by Serre et al. did not feature pelvic instrumentation, despite pelvic fractures being observed[17]. As such, the understanding of pelvic injury tolerance would benefit from further cadaver testing. Furthermore, given the established limits associated with cadaver testing, isolated tests using individual cadaver pelvises would be a valuable starting point for determining the material properties of the pelvis. Development of more well defined material property values for the pelvis is important for understanding pelvic injuries, as such properties can help inform the design of ATDs, protective clothing, and even the motorcycle itself.

References

  1. ↑ Mejia D, Ordoñez C, Padilla N, et al. Hemodynamically Unstable Pelvic Fracture: A Damage Control Surgical Algorithm that Fits your Reality. Colomb Medica. 2020;51. doi:10.25100/cm.v51i4.4510
  2. ↑ Perry K, Mabrouk A, Chauvin BJ. Pelvic Ring Injuries. In: StatPearls. StatPearls Publishing; 2022. Accessed November 23, 2022. http://www.ncbi.nlm.nih.gov/books/NBK544330/
  3. ↑ Rizzi M, Kullgren A, Tingvall C. The combined benefits of motorcycle antilock braking systems (ABS) in preventing crashes and reducing crash severity. Traffic Inj Prev. 2016;17(3):297-303. doi:10.1080/15389588.2015.1061660
  4. ↑ 4.0 4.1 4.2 Bréaud J, Montoro J, Lecompte JF, et al. Posterior urethral injuries associated with motorcycle accidents and pelvic trauma in adolescents: analysis of urethral lesions occurring prior to a bony fracture using a computerized finite-element model. J Pediatr Urol. 2013;9(1):62-70. doi:10.1016/j.jpurol.2011.12.003
  5. ↑ Hurson C, Collins D, McElwain JP. Crotch rocket2 pelvic fractures. Inj Extra. 2004;35(2):17-19. doi:10.1016/j.injury.2003.11.016
  6. ↑ Lenkeit JF, Hagoski BK, Bakker AJ. A Study of Motorcycle Rider Braking Control Behavior. Published online March 2011. Accessed November 9, 2022. https://trid.trb.org/view/1103120
  7. ↑ 7.0 7.1 7.2 7.3 Meredith L, Baldock M, Fitzharris M, et al. Motorcycle fuel tanks and pelvic fractures: A motorcycle fuel tank syndrome. Traffic Inj Prev. 2016;17(6):644-649. doi:10.1080/15389588.2015.1136061
  8. ↑ Wobrock JL, Mal A, Kraus J, Wu B. Pelvic Injury Potential and Motorcycle Gas Tanks. In: IRCOBI Conference Madrid 2006. ; 2006:4.
  9. ↑ 9.0 9.1 National Safety Council analysis of NHTSA Fatality Analysis Reporting System (FARS) data. Motorcycles. Injury Facts. Published May 26, 2022. Accessed November 9, 2022. https://injuryfacts.nsc.org/motor-vehicle/road-users/motorcycles/
  10. ↑ Ankarath S, Giannoudis PV, Barlow I, Bellamy MC, Matthews SJ, Smith RM. Injury patterns associated with mortality following motorcycle crashes. Injury. 2002;33(6):473-477. doi:10.1016/S0020-1383(02)00048-7
  11. ↑ Ouellet J. Groin injuries in motorcycle accidents. In: American Association for Automotive Medicine Proceedings. ; 1981.
  12. ↑ Fatality Facts 2020: Motorcycles and ATVs. IIHS-HLDI crash testing and highway safety. Accessed November 9, 2022. https://www.iihs.org/topics/fatality-statistics/detail/motorcycles-and-atvs
  13. ↑ de Peretti F, Hovorka I, Cambas PM, Nasr JM, Argenson C. Short device fixation and early mobilization for burst fractures of the thoracolumbar junction. Eur Spine J. 1996;5:112-120.
  14. ↑ 14.0 14.1 14.2 Whyte T, Kent N, Cernicchi A, Brown J. Mitigating fuel tank syndrome pelvic injuries – is there potential for rider worn protectors? Traffic Inj Prev. Published online June 10, 2022:1-6. doi:10.1080/15389588.2022.2072834
  15. ↑ Schmitt, Kai-Uwe; Niederer, Peter F.; Cronin, Duane S.; Morrison III, Barclay; Muser, Markus H.; Walz, Felix (2019). Methods in Trauma Biomechanics. Springer International Publishing. pp. 15–61. ISBN 978-3-030-11659-0.
  16. ↑ Petit L, Zaki T, Hsiang W, Leslie MP, Wiznia DH. A review of common motorcycle collision mechanisms of injury. EFORT Open Rev. 2020;5(9):544-548. doi:10.1302/2058-5241.5.190090
  17. ↑ 17.0 17.1 Serre T, Masson C, Perrin C, Martin JL, Moskal A, Llari M. The motorcyclist impact against a light vehicle: Epidemiological, accidentological and biomechanic analysis. Accid Anal Prev. 2012;49:223-228. doi:10.1016/j.aap.2012.08.013
  18. ↑ 14:00-17:00. ISO 13232-2:2005. ISO. Accessed November 9, 2022. https://www.iso.org/cms/render/live/en/sites/isoorg/contents/data/standard/03/74/37422.html
  19. ↑ Nolan M, Nitz J, Choy NL, Illing S. Age-related changes in musculoskeletal function, balance and mobility measures in men aged 30–80 years. Aging Male. 2010;13(3):194-201. doi:10.3109/13685531003657818
  20. ↑ Fischer B, Mitteroecker P. Allometry and Sexual Dimorphism in the Human Pelvis. Anat Rec. 2017;300(4):698-705. doi:10.1002/ar.23549
  21. ↑ Hsieh CH, Hsu SY, Hsieh HY, Chen YC. Differences between the sexes in motorcycle-related injuries and fatalities at a Taiwanese level I trauma center. Biomed J. 2017;40(2):113-120. doi:10.1016/j.bj.2016.10.005
  22. ↑ 22.0 22.1 de Rome L, Ivers R, Fitzharris M, et al. Motorcycle protective clothing: Protection from injury or just the weather? Accid Anal Prev. 2011;43(6):1893-1900. doi:10.1016/j.aap.2011.04.027


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