$152 Journal o f Biomechanics 2006, Vol. 39 (Suppl 1) Oral Presentations

desirable. It is our hypothesis that finite element (FE) analysis of fracture stability in combination with adhesive fixation can decrease open surgical interventions. Method: An FE-model of the human neck I was used to study how the location of fractures on C1 and C2 influences the spinal stability. Anterior and posterior arch fractures on C1 were modeled as well as dens type I and II fractures. The models were subjected to 10 Nm axial rotation, lateral bending, extension, and flexion applied at the center of gravity of the skull. T1 was locked in all degrees of freedom. Joint rotations and ligament strain was studied. Then, generic fractures were created in deer specimens and bonded with adhesives on the fracture site or patched with fiber reinforced adhesives on the side of the vertebra. Specimens were subjected to tensile testing and failure data was recorded. Results: The rotation of the head compared to T1 was affected less than 7 degrees. An inferior dens II fracture gave significantly more unstable kinemat- ics than a superior location. Single Cl-fracture had minor influence on the kinematics whereas several fractures shifted the C0-C1-C2 motion. The dens fractures increased strain in all the upper cervical ligaments except the alar ligament with decreased strain. Cl-fractures increased alar and C1-C2 level strains. Fiber reinforced adhesive patching performed better than fracture site bonding, with strengths up to 4 N/mm circumferential lengths. These results are promising for the application of upper cervical fracture fixation. Conclusion: FE-simulations can provide realistic data on spinal stability that could reduce the number of open surgical interventions. When fixation is needed fiber reinforced adhesives are attractive due to less invasive surgery.

References [1] Brolin, Halldin. Spine 2004; 29(4): 376-385.

4537 Tu, 12:15-12:30 (P19) Compar ison o f the mechanical performance of the Q3 and Hybrid III 30 three-yr-old dummy necks

J. Kadlowec 1, M. Maltese 2, A. DeSimone 1 , S. Rowson 1 , J. Saffioti 1 . 1 Rowan University, Glassboro, N J, USA, 2 Children's Hospital of Philadelphia, Philadelphia, PA, USA

Pediatric Anthropomorphic Test Devices (ATDs) are valuable tools for as- sessing the injury mitigation capability of automotive safety systems in the production of safe vehicle designs. Presently, two ATD necks exist which represent the three year old child and both pass accepted biofidelity tests, thus certifying them as human-like. Yet, both necks perform differently in the crash test environment and have been shown to evaluate differently the injury potential of safety systems. Objective: Compare the performance of Q3 and Hybrid III 3C ATD's necks under a controlled and repeatable test procedure that simulates a typical frontal impact crash of a torso-harness-restrained ATD. Hypothesis: The Hybrid III 3C and Q3 ATD head neck complexes behave differently in a simulated frontal impact experiment despite similar performance in biofidelity tests. Methods: Controlled tests of the ATD head/neck complexes in a controlled laboratory environment were conducted using a Part 572 Neck Pendulum test apparatus. The neck anterior-posterior acceleration, axial force, anter ior- posterior neck shear, flexion/extension bending moment, bending angle and shape of the Q3 and Hybrid III 3C neck were compared and contrasted. Conclusions: The Hybrid III three-year-old experienced a larger initial accel- eration and shear force in the anterior-posterior direction at the connection of the head and neck, perhaps due the fact that mass of the Hybrid III head is greater than that of the Q3 and the neck of the Hybrid III absorbed more of the impact force than the Q3. The Hybrid III head and neck experience a greater force than the Q3, while their neck lengths are approximately equal, thus the Hybrid III experiences a higher bending moment. This research adds scientific data to the contemporary debate surrounding the incorporation of these two ATD's and their suitability for restraint development and regulation testing.

4180 Tu, 12:30-12:45 (P19) Mobi l i ty o f unstable fractures of the odontoid during helmet removal - A cadaver study

U. Schmucker 1 , G. Matthes 1 , L.L. Latta 2, W. Gfr6rer, A. Ekkernkamp 1 , D. Richter 1 . 1Emst-Moritz-Amdt-University Greifswald, Orthopaedic and Trauma Surgery, Greifswald, Germany, 2Max Biedermann Institute for Biomechanics, University of Miami, FL, USA

Introduction: In severe motorcyclist accidents unstable injuries of the cervical spine can usually not be excluded before an X-ray has been taken in the hospital. Despite this the helmet has to be taken of fat the place of the accident in order to provide adequate treatment and airway management of the injured driver. There are no data in the current literature showing what happens to unstable lesions of the cervical spine during helmet removal.

Methods: For mobility measurements of the cervical spine, 2.7mm-screws were placed in the first three vertebral bodies (C1-C3) of 10 fresh frozen cadavers with intact soft tissues. In the next step an odontoid fracture Anderson Type II was created by osteotomy. Finally a motorcycle helmet was applicated. Fracture mobility in C 1-2 and C 2-3 was recorded under fluoroscopy after each step: physiological mobility of intact cervical spine (step 1), pathological mobility with unstable C 1-2 (step 2) and mobility during helmet removal (step 3). Results: Average motion during a full range of extension-flexion movement of the cervical spine: intact segment C1-2:10.20 ± 4.3°; unstable segment C 1-2: 23.7°±5.1° without dislocation and enormous increase of extension movement (+181%). After application of helmet there was one case of dislocation of C 1-2 in neutral supine position already, and two further cases of dislocations during helmet removal. Average motion of C 1-2 during helmet removal was 19.0°±7.90 (2-25°), median 18.0 °, great increase of flexion movement (+106%). No relevant changing of mobility was seen in segment C 2-3. Conclusion: Beside dislocations the average motion in the unstable C1-2 of 190 during professional removal of the helmet is frightening for the emergency physician. In order to avoid secondary neurological lesions cutting the helmet may be an alternative "removal technique". Also modified helmet construction with detachable parts may result in less manipulation of the head.

5.4. Head/Brain Injury: Macro-Biomechanics 7340 Tu, 14:00-14:30 (P21) Head injuries in car accidents - Biomechanics, research and car safety standards A. Wittek. School of Mechanical Engineering, The University of Western Australia, Crawley, Perth, Australia

Head injuries (i.e. skull and brain injuries) are one of the most common injury types and causes of death in car accidents. In order to reduce severity of such injuries, test procedures for evaluation of car crash safety performance in terms of risk of head/brain injuries have been introduced as part of car safety standards. Such procedures involve application of either full-scale tests using crash test dummies or subsystem tests using headform impactors (mechanical substitutes of the human head). All of them rely on Head Injury Criterion (HIC): a criterion that relates the resultant translational acceleration of head mass centre to the skull fracture risk. Important advantage of this criterion is its simplicity: the resultant translational acceleration of mass centre of crash test dummy head can be accurately determined using three accelerometers, and repeatability of the results is typically good. However, introduction of airbags resulted in decrease in the number of skull fractures and created a need for new criteria that would accurately predict the risk of brain injuries that occur without skull fracture. These new criteria often require determining deformation field within the brain during impact. Since such field is extremely difficult to determine by means of head mechanical substitutes, computer models (finite element method is typically used) have been proposed. Although several such models have been developed in the recent years by industry and academia, their implementation in car design has been very limited. The present study is one of the first attempts to conduct systematic analysis of the problems encountered when implementing the results of medical and biomechanical research on head/brain injury in procedures and tools (including finite element models) for evaluation of car crash safety performance, and to discuss possible solutions to these problems. This includes the following topics: • Implications of medical and biomechanical studies on traumatic head/brain

injuries for development of injury criteria used in car crash safety; • Requirements for criteria and tools for evaluating car crash safety perfor-

mance in terms of head/brain injuries, which includes tools (finite element models) that can be used during car design;

• Determining and modelling of brain-skull boundary conditions and constitu- tive behaviour of brain tissue and cerebral meninges.

6769 Tu, 14:30-15:00 (P21) Mechanisms of head injury for restrained pediatric occupants

K.B. Arbogast 1,2, R.A. Menon 1 , P. Jain 1 , '~ Ghati 1 . 1 Center for Injury Research and Prevention, The Children's Hospital of Philadelphia, Philadelphia, PA, USA, 2The University of Pennsylvania School of Medicine, Philadelphia, PA, USA

Traumatic brain and skull injuries are the most common serious injuries sustained by children in motor vehicle crashes regardless of age group or crash direction. These head injuries range from mild brain injury (defined as concussion or brief loss of consciousness) to skull fractures and more severe brain injuries. To address head protection for children, regulations typically use the Head Injury Criterion (HIC), scaled from adult and subhuman primate data and based on tolerance for skull fracture. It is unclear whether HIC adequately predicts the occurrence of head injury in pediatric occupants. To this end, a