Tech. EUETIB, Barcelona, Spain c Japan Automobile Research Institute, Tsukuba, Ibaraki, Japan. Available online: 29 Nov 2011

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1 This article was downloaded by: [University of Virginia, Charlottesville] On: 06 April 2012, At: 06:29 Publisher: Taylor & Francis Informa Ltd Registered in England and Wales Registered Number: Registered office: Mortimer House, Mortimer Street, London W1T 3JH, UK Traffic Injury Prevention Publication details, including instructions for authors and subscription information: Kinematics of the Unrestrained Vehicle Occupants in Side-Impact Crashes P. O. Riley a, C. Arregui-Dalmases a b, S. Purtserov a, D. Parent a, D. J. Lessley a, G. Shaw a, J. Crandall a, Shinichi Takayama c, Koshiro Ono c, Koichi Kamiji d & Tsuyoshi Yasuki d a Center for Applied Biomechanics, University of Virginia, Charlottesville, Virginia b Department of Mechanical Engineering, Universitat Politècnica de Catalunya, Barcelona Tech. EUETIB, Barcelona, Spain c Japan Automobile Research Institute, Tsukuba, Ibaraki, Japan d Japan Automobile Manufacturers Association, Jidosha Kaikan (NBF Tower), Minato-ku, Tokyo, Japan Available online: 29 Nov 2011 To cite this article: P. O. Riley, C. Arregui-Dalmases, S. Purtserov, D. Parent, D. J. Lessley, G. Shaw, J. Crandall, Shinichi Takayama, Koshiro Ono, Koichi Kamiji & Tsuyoshi Yasuki (2012): Kinematics of the Unrestrained Vehicle Occupants in Side- Impact Crashes, Traffic Injury Prevention, 13:2, To link to this article: PLEASE SCROLL DOWN FOR ARTICLE Full terms and conditions of use: This article may be used for research, teaching, and private study purposes. Any substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form to anyone is expressly forbidden. The publisher does not give any warranty express or implied or make any representation that the contents will be complete or accurate or up to date. The accuracy of any instructions, formulae, and drug doses should be independently verified with primary sources. The publisher shall not be liable for any loss, actions, claims, proceedings, demand, or costs or damages whatsoever or howsoever caused arising directly or indirectly in connection with or arising out of the use of this material.

2 Traffic Injury Prevention, 13: , 2012 Copyright C 2012 Taylor & Francis Group, LLC ISSN: print / X online DOI: / Kinematics of the Unrestrained Vehicle Occupants in Side-Impact Crashes P. O. RILEY, 1 C. ARREGUI-DALMASES, 1,2 S. PURTSEROV, 1 D. PARENT, 1 D. J. LESSLEY, 1 G. SHAW, 1 J. CRANDALL, 1 SHINICHI TAKAYAMA, 3 KOSHIRO ONO, 3 KOICHI KAMIJI, 4 and TSUYOSHI YASUKI 4 1 Center for Applied Biomechanics, University of Virginia, Charlottesville, Virginia 2 Department of Mechanical Engineering, Universitat Politècnica de Catalunya, Barcelona Tech. EUETIB, Barcelona, Spain 3 Japan Automobile Research Institute, Tsukuba, Ibaraki, Japan 4 Japan Automobile Manufacturers Association, Jidosha Kaikan (NBF Tower), Minato-ku, Tokyo, Japan A test series involving direct right-side impact of a moving wall on unsupported, unrestrained cadavers with no arms was undertaken to better understand human kinematics and injury mechanisms during side impact at realistic speeds. The tests conducted provided a unique opportunity for a detailed analysis of the kinematics resulting from side impact. Specifically, this study evaluated the 3-dimensional (3D) kinematics of 3 unrestrained male cadavers subjected to lateral impact by a multi-element load wall carried by a pneumatically propelled rail-mounted sled reproducing a conceptual side crash impact. Three translations and 3 rotations characterize the movement of a solid body in the space, the 6 degrees of freedom (6DoF) kinematics of 15 bone segments were obtained from the 3D marker motions and computed tomography (CT)-defined relationships between the maker array mounts and the bones. The moving wall initially made contact with the lateral aspect of the pelvis, which initiated lateral motion of the spinal segments beginning with the pelvis and moving sequentially up through the lumbar spine to the thorax. Analyzing the 6DoF motions kinematics of the ribs and sternum followed right shoulder contact with the wall. Overall thoracic motion was assessed by combining the thoracic bone segments as a single rigid body. The kinematic data presented in this research provides quantified subject responses and boundary condition interactions that are currently unavailable for lateral impact. Keywords INTRODUCTION Side impact; Kinematics; Cadaver; Pelvis impact; Shoulder impact; Spine motion Side Impact Importance Side-impact collisions are very common (Rouhana and Foster 1985; Rouhana et al. 1985) and result in fatalities more frequently than frontal impacts (Bedard et al. 2002). For immediately fatal injuries, head and neck injuries are the most prevalent, followed by thoracic injuries (Warner et al. 1989). Injuries to the shoulder, abdomen, and pelvis contribute to nonfatal morbidity. There is evidence that the growing aged population is particularly vulnerable to side impact trauma (Fildes et al. 2006). Thus, there is a well-recognized need to improve vehicle safety standards and to develop occupant protection technologies for side-impact collisions. Achieving these objectives, however, has proven difficult. US and European agencies have developed very different tho- Received 22 July 2011; accepted 30 October Address correspondence to Patrick O. Riley, University of Virginia Center for Applied Biomechanics, 4040 Lewis and Clark Drive, Charlottesville, VA por2n@virginia.edu 163 racic injury criteria (Kent and Crandall 2003). In turn, different risk prediction methods have led to correspondingly different countermeasures (Horstemeyer et al. 2009). Studies with frangible human models for example, cadavers, also referred to as postmortem human surrogates (PMHSs) are essential in developing valid injury criteria (Kent and Crandall 2003) as well as in defining the human body impact response characteristics. PMHS Side-Impact Studies Early studies of side-impact kinematics were conducted with human volunteers (Ewing et al. 1979). PMHS tests have been shown to represent the response of human subjects (Bendjellal et al. 1987). Because PMHS tests do not reflect the effect of muscle activation, they tend to overestimate kinematic parameters. Tests with human volunteers have continued (Fugger et al. 2002) and remain the standard for evaluating ATD biofidelity (Bolte et al. 2000, 2003; Parenteau 2006). Tests with human volunteers, however, are limited to noninjurious conditions. Thus, PMHS tests are necessary to explore the full range of survivable impacts and to develop injury criteria (Cavanaugh et al. 1993; Compigne et al. 2004).

3 164 RILEY ET AL. Side-impact collisions in the real world are inherently very complex, thus motivating laboratory studies using both volunteers and PMHSs to focus on various specific aspects such as difference in near side and far side occupant behavior (Fugger et al. 2002), pelvis impact and lumbar motion (Fildes et al. 2006; Leport et al. 2007; Majumder et al. 2004, 2008), shoulder impact and thoracic deformation (Bolte et al. 2000, 2003; Cavanaugh et al. 1993; Duprey et al. 2010; Kemper et al 2008; Koh et al. 2005; Marth 2002; J. Shaw et al. 2006; Thollon et al. 2001; Viano and Lau 1985), and head and neck motion (Bendjellal et al. 1987; Ewing et al. 1978; Yoganandan et al. 2009; Zou and Schmiedeler 2008). Need for Detailed Kinematics The need to measure the detailed kinematics of both the structures and the occupants during side impact is recognized (Warner 1990). In practice, however, motion analysis of highspeed vehicle occupant impacts is quite complicated. Vehicle structures obstruct and limit the number and size of fields of view, restricting kinematic analysis to 2D measurements from a limited number of cameras. 2D measurements have errors due to out-of-plane motion. Skin marker based measurements, whether 2D or 3D, have errors due to skin motion artefacts compounded by impact and inertia-induced musculoskeletal deformations. We have developed a 3D kinematic analysis approach in which arrays of kinematic markers are rigidly attached to PMHS bone segments (G. Shaw et al. 2009). The lateral aspect of each PMHS was struck by a moving, nonyielding, multielement load wall to provide an opportunity to observe the lateral impact response of unsupported and unrestrained human bodies. The objective of the current study is to provide comprehensive characterization of human kinematics response to wholebody lateral impact. This characterization provides quantified subject responses and boundary condition interactions for a survivable and potentially injury-free 4.3 m/s side impact. Methods Side-impact test baseline. Three adult male PMHS were subjected to right-side pure lateral impacts. Each stationary seated subject was struck at 4.3 ± 0.1 m/s by a rigid wall mounted to a 1700-kg rail-mounted sled. The test methodology of this research was described by Lessley et al. (2010); a brief summary of the relevant information provided is included here for better understanding of the experiment. Figure 1 reproduces the experiment baseline. Each subject was positioned on a rigid seat inclined at 15 degrees (relative to the horizontal) and was held stationary by a system of polyester tethers until immediately prior to being impacted by the moving wall. The tether mechanism was released approximately 10 ms prior to impact, minimizing deviation from the positioned posture at impact. The seat was attached to a lightweight rail-mounted sled (seat sled) that also supported a subject capture system used Figure 1 Experiment baseline: (a) initial contact barrier pelvis, (b) maximum chest deformation, and (c) barrier design detail, all the plates were instrumented with load cells. (A) indicates a plate as an example. to gently decelerate the subject following the wall impact to prevent artifactual injury. The load wall fixed to a 1700-kg rail-mounted sled was designed to provide near constant velocity throughout the impact event. The current study loaded the shoulder, thorax, abdomen, pelvis, and lower extremities but subdivided the loading surfaces in order to better assess load distribution at a local level. The load wall consisted of an adjustable matrix of 15 individual plates, each supported by a 5-axis load cell (3 forces and 2 moments) that recorded the interaction between the subject and impacting wall. The plates were adjusted vertically and anteriorly/posteriorly so that they could be adjusted to the different subjects anthropometries; the different PMHS anthropometries are provided in Table I. Body mass indexes (BMIs) were provided to characterize the subjects, and it was observed that they were within the accepted normal range of 18 to 24. A 59-gage chestband (Eppinger 1989; Hammett 1989; Pintar et al. 1997) located at the level of the sixth lateral rib was also used to measure thoracic deformation. Vicon setup and marker plates. Event kinematics were recorded using a 16-camera ViconMX motion capture system (Vicon, Los Angeles, CA) and arrays of retroreflective markers rigidly attached to bone. The 6 degree of freedom (6DoF) bone

4 UNRESTRAINED VEHICLE OCCUPANTS 165 Table I PMHS characteristics Test Mass a (kg) Age (yr) Height (cm) BMI Cause of death Stroke Brain aneurysm Laryngeal cancer a As tested with arms amputated. kinematics were obtained from the 3D marker trajectories using rigid-body analysis (Shaw et al. 2009). The cameras were arrayed around the impact area, creating a viewing volume that allowed capture of more than 10 cm of the wall approach (prior to contact with the seated subject) and the complete kinematics of the PMHS from the time of initial impact to the time of final capture in the fabric containment. Motion capture data were obtained at 1000 Hz using the Vicon workstation. Mount plates sufficient to support the mass of the marker arrays, but small compared to the bony structure, were affixed directly to the skull, sacrum, sternum, and right and left scapula with short screws. Two long screws each attached external mount plates to the 1st, 6th, and 11th thoracic and 3rd lumbar vertebrae (Figure 2). Mounting plate designs and vertebral screw placements minimized the effect on bony structure and soft-tissue entrainment to avoid affecting the structural stiffness. To prevent stress concentrations due to measurement hardware, mount plates were attached to ribs via high-strength nylon wire ties that secured the measurement hardware to the rib. Standoffs through the incised but loosely sutured overlying flesh attached rigid marker plates to the mounts. Each marker plate supported a cluster of four retroreflective markers. Fifteen marker clusters were used to obtain the 6DoF kinematics of 15 bone segments (Figure 2). Multiple markers were placed on each sled to define reference coordinate systems and to allow the 6DoF kinematics of both the wall and seat to be determined. Figure 2 Location of motion capture marker arrays and single markers on body (left). Motion capture marker array attachment to vertebral, sternal, and rib mounts (right). Rib bone coordinate system assumed to be aligned to the mount plate, which was tie-wrapped to bone. Mounts for motion capture marker arrays were visualized in the same set of CT scans as the bone, allowing derivation of mount-to-bone transformations. Figure 3 Local coordinate systems for head, sternal, vertebral, and pelvic 6DoF segments. Segment coordinate systems defined by bony landmarks on CT scans. Kinematic transformations. After mount installation, a whole-body computed tomography (CT) scan was obtained for each PMHS at 1-mm spacing (LightSpeed 16, GE Medical Systems, USA). The mounts and bony segments of interest were identified and their surfaces modeled using Mimics and Magics software (Materalize, N.V., Leuven, Belgium). The 3D locations of the mount and landmarks on associated bones were used to define bone segment coordinated systems (Figure 3) and the mount-to-bone transformation. In general, the X-axis is positive forward, the Y-axis is positive to the subject s right, and the Z-axis is positive downward (Cappozzo et al. 1995). The marker cluster to marker plate transforms were determined using precision mechanical linkage (FARO Technologies, Inc., Lake Mary, FL) measurements. FARO measurements were also used to define the sled marker configurations. The marker plate to-mount transformations were determined from the known standoff geometry.

5 166 RILEY ET AL. Kinematic data processing. The motion capture data were postprocessed using Vicon Nexus, yielding standard c3d files (C3D.org) containing the labeled 3D trajectory of each marker. No filtering or smoothing was employed. Using an in-house processing stream encoded in MATLAB (Mathworks, Natick, MA) the marker plate position and orientation were determined (G. Shaw et al. 2009). Because 4 markers were used in each cluster, though only 3 were required, the process was robust to marker dropout, and optimized positions were obtained. The appropriate transforms were then used to infer bone kinematics from the marker plate motion. To characterize overall thorax motion and deformation, a pseudo-rigid body was defined using the positions of T1, T6, T11 and the sternum. The segment origin was located at T6. The T1-T11 vector defined the Z-axis direction, the T6-sternum vector defined the X-axis direction, and the Y-axis is given by the right-hand rule. RESULTS Hip Impact and Lateral Deformation of the Spine The data were synchronized to the time of pelvis initial contact. The data for 100 ms after contact are shown covering the impact event. The Y-axis (along the track, down track negative) velocities of the impacting segments the wall, pelvis, and right scapular segments define the temporal pattern of each trial (Figure 4). The vertical line indicates the time when shoulder velocity became consistently negative. This presumptive time of shoulder impact was consistent with load wall force data. Slight variations in subject height and initial posture produced different delays in the start of shoulder (scapular segment) motion; 14, 10, and 28 ms, respectively for trials 1413, 1414, and For tests 1413 and 1414, pelvis and shoulder reached wall velocity (approximately 4.4 m/s) at approximately the same times (70 and 60 ms, respectively), implying much higher acceleration of the shoulder. For test 1415, the shoulder acceleration was also higher than the pelvis acceleration (9 ms vs. 30 ms to reach wall speed), but due to the 28-ms delay in start of motion, the shoulder reached wall speed 7 ms after the pelvis. Following pelvis impact, spinal segment motion was observed to begin sequentially. L3 motion began approximately 5 ms after the start of pelvis motion (Figure 5). Thorax (T6) motion was delayed until after shoulder contact for tests 1413 and 1414 but began before shoulder contact in test Among the spinal segments, roll rotations of 20 degrees and yaw rotation between 10 and 20 degrees were observed. Thorax Motion and Shoulder and Thorax Deformation Due to subject posture, the thorax was inclined away from the load wall for test 1413 and more significantly so in test 1415 (Figure 6), which contributed to the relative delay in shoulder impact seen in these trials. The thorax displacements were similar for all trials with substantial displacement to the PMHS s left (negative Y-axis), less substantial posterior (negative X-axis) Figure 4 Track axis velocities of the wall buck, pelvis, and shoulder for each trial. Wall velocity (dash-dot-dot line) negative. Pelvis (solid line) accelerates to wall velocity after impact. Due to subject size and initial position, the delay to shoulder impact (dashed line) varied among subjects. Vertical line indicates approximate time of shoulder impact. and very little vertical (Z-axis axis) displacement. Thoracic deformation, as measured by the displacements of the thoracic segments in the thorax coordinate system, exhibited two phases. From shoulder impact to approximately 60 ms, thoracic deformation was primarily due to impact-induced deformation and rebound. After time 60 ms there was evidence of deformation due to postural changes as the thorax rotated and was displaced. Peak deformations >2.5 cm were seen in the sternum and rib segments. Table II shows the impact side peak rib displacements compared to rib displacements measured by the chestband. Because the marker arrays were placed on the anterior thorax, rib cage displacements measured with Vicon were primarily anterior posterior. The peak displacements recorded by the chestband were in the medial lateral direction on the struck side. The magnitude of shoulder displacement and rotations relative to the thorax (Figure 7) was similar for tests 1414 and Table II Rib and chestband peak displacement magnitudes Location Test 1413 (mm) Test 1414 (mm) Test 1415 (mm) Sternum Right fourth rib Right ninth rib Chestband anterior Chestband lateral Chestband posterior

6 UNRESTRAINED VEHICLE OCCUPANTS 167 Figure 5 Displacements of the pelvis. Lumbar and thoracic spinal segments. Vertical line indicates approximate time of shoulder impact. Negative Y displacement (dashed line) indicates movement down the track. Negative X displacement (solid line) indicates movement to the subject s back. Positive Z displacement (dashdot-dot line) indicates movement toward the ground. There was significant disruption of the shoulder ligaments in test 1413, which exhibited the largest medial lateral (Y-axis) excursion and the most extreme rotations. The differences in the magnitude and direction of anterior posterior (X-axis) and vertical (Z-axis) displacements may be due to the variation in initial thorax orientation. DISCUSSION The Vicon kinematic data presented herein represent a significant component of the results from these heavily instrumented tests. Some responses were, however, measured with redundant instrumentation (C. G. Shaw et al. 2010). For example, in addition to the Vicon system, spine and head kinematics were inferred from accelerometers and angular rate sensors, and chest deformation was also measured with a 59-gage chestband. High-speed video, also acquired at 1000 fps, was not used for quantitative analysis. This and similarly instrumented studies will determine where different measurement modalities complement each other or are redundant and, where redundancies exist, which provides the most accurate, reliable, and useful output. In addition, segmental kinematics may be used to define

7 168 RILEY ET AL. Figure 6 Kinematics of the thorax as a rigid body and the magnitudes of deformations of the thoracic bone segments relative to the thorax. Thorax angles are Euler angles referenced to the global coordinate system. Thorax linear displacements are offsets from the initial position (0,0,0) referenced to the global coordinate system. Segment displacements are changes in the distance from each thoracic rigid body to the thorax origin-t6 (color figure available online). injury criteria that are more physiologically relevant than, for example, peak accelerations. Spinal Injury Implications The risk of hip and pelvic fracture due to lateral impact is widely recognized, well understood, and adequately modeled (Leport et al. 2007; Majumder et al. 2004, 2008). These kinematic data reveal that the spine is deformed by an isolated hip impact. Current anthropometric test devices (ATDs, crash test dummies) do not model spinal stiffness with adequate fidelity to simulate this behavior or predict the associated injury potential (Fildes et al. 2006; Pintar et al. 2007; Sundararajan et al. 2005). 6DoF kinematic data provide a powerful tool for studying spinal deformations, allowing the displacements and rotations of spinal segments to be assessed. With appropriate instrumentation, intervertebral compression and extension can be measured.

8 UNRESTRAINED VEHICLE OCCUPANTS 169 Shoulder and Clavicle Injury Implications Two forms of thoracic injury that can arise from near side lateral impact are shoulder girdle injury and rib fracture (Astier et al. 2008; Duprey et al. 2010; Scarlat et al. 1999; Thollon et al. 2001). The Vicon kinematic data provides insight into both injury mechanisms. Damage to the acromioclavicular and sternoclavicular joints is common in shoulder impacts, as is fracture of the clavicle (Bolte et al. 2000, 2003; Thollon et al. 2001). We observed peak medial lateral deflections of the acromion relative to the thorax of 50 to 70 mm with vertical displacements of 38 to 49 mm. For impacts between 4.2 and 4.75 m/s, Bolte et al. (2000) reported acromion deflection relative to the sternum between 12 and 56 mm. In that study, clavicular fractures occurred at displacements of 20 to 30 mm, preceding peak displacements ranging from 36 and 56 mm. We observed no clavicular fractures; however, the test with the largest peak medial lateral displacement, PMHS 1413, resulted in extensive disruption of the shoulder structures. We observed peak mid-sternum displacements relative to the thorax ranging from 20 to 31 mm. For a 6.7-m/s rigid-body lateral impact, Irwin et al. (1993), using 3D analysis of singlebone pin markers, reported an 85-mm displacement of the lower sternum. We measured peak displacements of the nonimpacted 10th rib of between 12 and 19 mm, whereas Irwin reported nonimpacted 8th rib displacements in the range of 160 mm. The difference in displacement magnitudes reflects the difference in energy between 4.4 and 6.7 m/s impacts, the more distributed loading of a load wall compared to a hub impactor, and differences in reference systems. Rib deflections measured by rigid-body kinematic analysis were greater for subject 1413 with multiple rib fractures, agreeing with the deformation measures provided by the strain gage-based chestband mounted between the 4th and 9th rib markers (Lessley et al. 2010). The response data suggest that the shoulder injury likely contributed to greater thoracic deflection and resulting rib fractures occurring in test The lateral displacement of the Figure 7 Displacements and rotations of the right acromion (right shoulder) relative to the thorax rigid body. The displacement components are referenced to the thorax coordinate axes and the pre-impact shoulder position (0,0,0).

9 170 RILEY ET AL. shoulder with respect to the spine was substantially greater for the injured subject in test 1413 than that of 2 uninjured subjects. This increased lateral displacement of the shoulder appears to have allowed the right upper extremity to become impinged and driven into the lateral ribcage. This effect is illustrated in the rib segment kinematics of test Rib cage distortion also occurred, however, in tests 1414 and 1415, in which no shoulder injury or resulting impingement of the upper extremity occurred. The response data suggest that the shoulder presents a substantial load path and plays an important role in transmitting lateral forces to the spine, shielding and protecting the ribcage as suggested by Melvin et al. (1998). Though rib fracture may be less likely without shoulder injury or arm impingement, it is still possible, particularly to occupants who are most vulnerable to rib fracture, such as the elderly (Sunnevang et al. 2009). The PMHS in test 1413 experienced the most lateral rib compression and was the only cadaver that developed rib fractures (Bloch and Cesari 1988). Study Limitations The protocol documented the behavior of an unconstrained body when impacted directly by a rigid impact wall traveling at 4.4 m/s. The studied event was designed to be less complex than a real-world side impact involving multiple structures and constraints. Though the isolated response of the body is not entirely unrepresentative of the real world, the results should not be taken out of context. Motion of thoracic segments, in some cases, began before shoulder impact. The behaviors of the shoulder girdle and thoracic segments were similar to those observed in pure shoulder and thorax impact studies. However, because of the motion introduced by pelvis impact, the data presented herein are not directly comparable to those obtained in those studies. The response of cadavers does not reflect the action of active muscles. 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