Newsletter Volume 13 - 1st Quarter 2007
Study of the whiplash mechanism with a detailed multi-body neck model
CONTENTS
Case Study: Study of the whiplash mechanism with a detailed multi-body neck model
Software: LifeMOD™, LifeMOD/NeckSIM™, and LifeMOD/KneeSIM™ v 2007 now shipping
BRG announces LifeMOD Employment Referral Network.
Publications: Journal Papers, Magazine Articles and Book Chapters
This issue of the newsletter presents a study of the whiplash mechanism using a detailed multi-body neck model. This model represents a new capability offered in the LifeMOD family of products called LifeMOD/NeckSIM. It was developed with a consortium of universities, commercial industries and government institutions. The model outlined in the work below is included as a self-training tutorial in the LifeMOD/NeckSIM product.
We would like to sincerely thank our partners and customers for helping us to exceed our own expectations for growth in 2006. To accommodate this rapid growth, we now have several employment opportunities available.
We would also like to announce a major release in our core product LifeMOD v. 2007, a major release in our total knee replacement solution, LifeMOD/KneeSIM v. 2007.0.1, and a brand new product, LifeMOD/NeckSIM v. 2007. The technology represented in these programs represent many man-years of development and reflect our commitment to responding to our active customer base as well as advancing the state-of-the-art in biomechanics simulation technology.
Also, our partnership with the Orthopaedic Research Laboratories (ORL), Cleveland Ohio, directed by A. Seth Greenwald continues to grow. The ORL has selected LifeMOD/KneeSIM as a basis for comparative studies between commercially available total knee replacement systems (TKR). They also have selected LifeMOD/NeckSIM as a basis of comparative studies for spinal devices.
To serve our growing customer base we have partnered with 11 new distributors around the world.
Finally, with the many employment inquiries from students and scientists, as well as inquiries from our many industry clients we have decided to link up the two with the LifeMOD Employment Referral Network.
CASE STUDY: THE WHIPLASH MECHANISM WITH A
DETAILED MULTI-BODY NECK MODEL
Introduction
"Whiplash" is not a whip or a lash. Early models of whiplash focused on sprain-strain injuries or an injury to the ligament (sprain) and to the muscle (strain). As a result, it was thought "Whiplash" occurred when the neck was hyper-extended (moved too far back). This was one of the reasons for adding headrests to cars. However, more recent research has shown that this doesn't happen [Kaneoka,'99]. In fact, the mechanism that causes "whiplash" is now known to be differential acceleration or deceleration, where the torso is pushed forward while the head lags behind. The neck will flex until either the facet joints in the back of the vertebrae or the anterior longitudinal ligament in the front of the vertebrae stop the motion. A clear account of the basic relative motions between the head, torso and vehicle seat back has been given by [Severy et al., '55]. The motion of the head and spine for a rear end automobile collision may be summed up in figure 1.
Figure 1. Occupant kinematics during a rear-end automobile collision.
This movement produces injury-causing shear forces on the neck and likely a pressure build-up of cerebral spinal fluid (the fluid that surrounds the spinal cord and nerve roots). These forces can injure the ligaments (anterior longitudinal ligaments), muscles (sternocleidomastoids and the longus colli) and facet joints as well as the dorsal root ganglion (nerves in the neck that transmit information about feeling) [Eichberger, '00]. The sternocleidomastoid muscles are the large strap like muscles running down the front of the neck that pop out when the jaw is flexed. They are used to turn and support the head. The longus colli is a muscle that runs directly in front of the spine is used to turn the head from side to side and to bend the neck forward (Figure 2). The longus colli muscle aids the sternocleidomastoids in holding up the head and moving the neck. Often, the longus colli muscle is weakened during whiplash and the sternocleidomastoid muscles become overworked as they compensate.
Figure 2. Locations of the Longus colli, sternocleidomastoid muscles (courtesy of Gray's Anatomy), the facet joints and the anterior longitudinal ligament (courtesy of spineuniverse.com).
To explore the injury propensity to the facet joints, ligaments and muscle during the rear-end vehicular collision, LifeMOD/NeckSIM will be used to simulate the condition and extract the loadings to these structures to compare against tissue physiological limits and injury norms. The model will be validated by comparing the global kinematics of the head (translational and angular motion and accelerations) as well as local kinematics such as vertebral rotations to data available from literature.
Features of this new model include:
- Multi-body (vertebrae) complete with non-linear visco-elastic disk forces, facet joints, nonlinear visco-elastic ligaments and contractile muscles with proper lines of action.
- Anthropometrically scalable (using any of the 5 LifeMOD databases)
- Personalizable (using MRI data)
- Validated (limited)
- Quick solving (less than 1 minute clock time per simulation)
- Generalized model can be used for rear-end, forward, and lateral collisions
- Parameterized model may be quickly adapted for other injury scenarios such as crash with turned head, cranial impacts, etc.
- Other applications include orthopaedic appliance evaluation such as fixation, stents, etc.
Model Description
Vertebrae
A full body model was created using LifeMOD using parameters
for a 50%-ile male from one of the internal anthropometric databases.
The neck segment is automatically discretized into individual vertebra
components, C1 - C7. Each component is modeled with the mass properties
of the neck "slice" at each region.
Disks Six degree-of-freedom disk forces are created to represent medial/lateral shear, axial tension/compression, anterior posterior shear, lateral bending, flexion/extension and axial rotation using data from De Jager, ['96].
Figure 3. Partial body model with discretized cervical vertebrae complete with 6 dof disk forces.
Facet Joints Facet joints are synovial joints formed by the corresponding articular facets of the adjacent vertebrae and enclosed by joint capsules. Contact in the facet joints is modeled by a generalized surface contact force in the region. Since little data is available for the mechanical properties of this joint, stiffness and damping properties are estimated based on experience modeling other articular contact joints in the body.
Figure 4. Facet joints are created using generalized surface contact forces between adjoining vertebrae facets.
Ligaments Ligaments are added to the model including the interspinous, flaval, anterior longitudinal ligaments. The force-displacement behavior of the ligaments was modeled using data from [Yoganandan, '01]. Viscous damping effects for the ligaments were modeled using data derived from [van der Horst, '02].
Figure 5. Model complete with ligament set. Ligaments create the force-displacement and viscous damping effects between the bone elements.
Muscles After the ligament set is created, muscles are created on the model. Muscles are modeled with Hill-Type elements [Hill, '38], depicted in figure 6. The basic Hill model is composed of three elements: two which are arranged in series which, in turn, are in parallel with the third element. The contractile element (CE) is freely extendable when at rest, but capable of shortening when activated by an electrical stimuli. The CE is connected to an elastic serial element (SE). The SE accounts for the muscle elasticity during isometric force conditions. These two elements are then joined in parallel with another elastic element used to account for the elasticity of the muscle at rest [Fung, '93]. Data for passive muscle behavior was largely drawn from [Brelin-Fornari, '98] and active muscle behavior from [Winters, '88, Winters, '85, Zajac, '89].
Figure 6. Hill's three element mechanical model.
The Hill muscle elements were attached to the bone using estimated (averaged) coordinates of origins and insertions based on detailed anatomy textbooks [Quiring, '47, Kapandji, '74]. Most muscles are represented by several muscle elements to account for distributed attachment zones to the bone. Each muscle element is divided into segments which are supported on vertebrae where there may be force transmission. These slide points enforce a more accurate line of action between the origin and insertion of the individual muscle element. This feature is illustrated in figure 7. The figure also displays the trapezius muscle group. Figure 8 displays the semispinalis capitis and the semispinalis cervicis muscle groups. Figure 9 displays the Longus colli and sternocleidomastoid muscle groups.
Figure 7. Trapezius muscle elements created initially (left), with pathway slide points (right).
Figure 8. Semispinalis capitis (left) and semispinalis cervicis (right) muscle groups. Also displayed are the muscular slide points.
Figure 9. Longus colli (left) and sternocleidomastoid (right) muscle groups. Also displayed are the muscular slide points.
Boundary Conditions To impose the loadings on the model of a rear-impact vehicular collision, a translational joint is created between the thoracic segment (lumped multi-body) and the ground (figure 10). A parameterized acceleration field is then applied to the joint for a variety of loading scenarios. To simulate frontal and lateral impact collisions, the joint is simply rotated.
Figure 10. Completed cervical vertebrae model with an acceleration field applied to a vertical translational joint between ground and the thoracic segment of the model.
Validation
For the purposes of this newsletter a simple but practical validation will be performed by comparing the kinematics of the model to the kinematics of a cadaver specimen [Luan, '00] and a human test subject [Ono, '97]. This will be done in terms of global response (comparing head/chest accelerations) and local response (motion of the vertebrae via radiographic images).
Cadaver Experimental Comparison - Global Response Cadaver sled experiments for a rear-impact collision [Luan, '00] was used for model comparison in figure 11. The acceleration profile of the experimental thoracic segment (T1) was used as input into the simulation. Posterior-anterior accelerations for the head were compared. It can seen in this comparison that the model agrees quite well with the experiment; demonstrating the phase lag between the head and the thoracic segment.
Figure 11. Comparing the human volunteer experiment to the model. The red curve represents the thoracic acceleration for both the model and the experiment (the experiment data was used as input to the simulation).
Human Experimental Comparison - Local Response The next step is to evaluate whether the model is recreating the proper S-shape, C-shape modalities of the vertebral alignment during the acceleration pulse. In [Ono, '97], human volunteers were used in a acceleration sled test in which x-ray data was used to obtain data on the cervical vertebrae kinematics during the pulse. Figure 12 displays a comparison between the human experiment data and the model response to the same crash pulse. It can be seen in the figure that the vertebrae kinematics compare quite favorably between the model and experiment.
Figure 12. The top sequence is the model kinematics reported during the impact condition. The bottom sequence is the kinematic trace of the model as compared to the kinematic trace of the live test subject using x-ray data.
Simulations - Rear End Collision
With the global and local model kinematics validated to a certain extent, it will now be exercised to extract the loads to the facet joints, the anterior longitudinal ligaments, the sternocleidomastoids and the longus colli muscle groups for a simulated rear-end impact. The model will be used to simulate a rear-end collision of 7g for a duration of 100 ms.
Injury criteria currently used in automotive safety equipment design and injury assessment (accident reconstruction) are still mostly based on global parameters such as relative accelerations [SAE, '86]. However, neck injuries associated with the whiplash condition are cased by local tissue loads (muscular and ligament) and facet joint loads. The relation between the global injury parameters and the local injury patterns is not known, since local tissue loads are difficult to measure. However, computational modeling techniques, such as the one described in this newsletter, can be very useful tools in providing insight to this relationship.
Kinematic Response The kinematic response for the acceleration field applied to the upper torso is displayed in figure 13. The S-curve to C-curve transition can be observed in the figure. Figure 14 displays the vertical accelerations of each of the segments in the model.
Figure 13. Successive frames of the 7g rear impact collision demonstrating the S-curve to C-curve transition.
Figure 14. Vertical (AP) accelerations of the upper torso, C1-C7 and the head segments.
Ligament Injury Assessment Figure 15 displays the loads to the anterior longitudinal ligament. Various source in literature [Yoganandan, '98] report failure loads to this ligament at about 94 lbf for the lower ligaments (T1-C5) and 55 lbf for the higher ligaments. The simulation results reported in figure 15 display that the maximum load on the lower ligaments is less than 25 lbf and 7.5 lbf for the higher ligaments indicating that the 7 G collision crash pulse was below the injury threshold for this tissue.
Figure 15. Dynamics loadings to the anterior longitudinal ligament.
Muscle Injury Assessment Figure 16 displays the loads to the longus colli and the sternocleidomastoid muscles on the left side. To assess the propensity towards injury for these tissues, the maximum loads reported will be compared against the tissue physiological cross sectional area as reported in [Meyers, '98] and the maximum isometric tissue stress reported in [Winters, '88]. These values are used in table 1 to compare the calculated maximum tissue loads to the simulation loads. It can be observed that for this particular case the loads are below the tissue strain thresholds.
Figure 16. Dynamics loadings to the Longus Colli and the Sternocleidomastoid muscles on the left side.| Tissue | PCSA | MAX Stress |
Max Load (PCSA * Max Stress) |
Simulation Load (Fig. 16) |
|
Longus Colli |
.425 | 259 | 110 lbf | 85 lbf |
|
Sternocleidomastoid |
.764 | 259 | 198 lbf | 150 lbf |
Table 1. Comparing the calculated maximum tissue load to the simulation loads for the muscles.
Facet Joint Injury Assessment
For the purposes of this newsletter, injuries to the facet joint
complex were determined by simply measuring the strain on the capsular
ligaments during the dynamic simulation. In the simulation peak strain
was greatest at the C7-C6 measure at about 125 lbf compared to reported
injury loads of 200 lbf [Person, '04].
Discussion
The study in this newsletter was put forth to present a commercially available, high-fidelity cervical spine model. A cursory validation study was performed by comparing the global response of the model to the global response of cadaveric experiments and the local response to radiographic images of a human test subject. With some confidence in the model it was used to determine tissue and joint loads to be compared against published injury norms for a 7 G rear end automobile collision.
The results from the 7 G rear collision yielded tissue loads for the facet joint capsule, the anterior longitudinal ligament, the sternocleidomastoid and longus colli muscle groups to be within the strength limitations if each tissue. This correlates to the statistical data [SAE '86] that major tissue strain typically does not occur for collisions of this intensity.
Obviously more validation and work must be performed to increase the level of confidence for the model's predictive capabilities. However since the model is fully parameterized, the model tuning process may be performed quite conveniently. With an increased level of confidence this model can become a powerful tool to providing insights into the specific injury mechanisms resulting from vehicular trauma.
References
- []Brelin-Fornari, JM, 1998, A lumped parameter model of the human head and neck with active muscles. PhD thesis, University of Arizona, USA, 1998.
- []De Jager MKJ, 1996, Mathematical Head-Neck Model for acceleration Impacts. PhD. Thesis: Eindhoven University of Technology, 1996.
- []Eichberger A, et al., 2000, Pressure measurements in the spinal canal of post-mortem human subjects during rear-end impact and correlation of results to the neck injury criterion. Accid Anal Prev. 2000 Mar;32(2):251-60.
- []Fung, Y.C. 1993. "Skeletal muscle", in Biomechanics: Mechanical Properties of Living Tissues. Berlin: Springer-Verlag.
- []Hill, AV, 1938, The heat of shortening and the dynamic constants of muscle, Proc Roy Soc B126:136-195.
- []Kaneoka K, et al., 1999, Motion analysis of cervical vertebrae during whiplash loading. Spine. 1999 Apr 15;24(8):763-9; discussion 770.i 10222526
- []Kapandji, IA, 1974, The Physiology of the Joints, Volume 3: The Trunk and the Vertebral Column. Churchill Livingstone, Edinburgh, 2nd edition, 1974.
- []Luan, F, et al., 2000, "Qualitative Analysis of Neck Kinematics During Low-Speed Rear-End Impact." Clin. Biomech. (Los Angel. Calif.), 15(9), pp. 649-657.
- []Myers, BS, 1998, Cervical spine muscle. Final Report F.2c, Duke University, Durham, North Carolina, USA, 1998.
- []Ono, K, et al., 1997, "Cervical Injury Mechanism Based on the Analysis of Human Cervical Vertebral Motion and Head-Neck-Torso Kinematics During Low Speed Rear Impacts," SAE Tech. Pap. Ser., Paper Number 973340.
- []Pearson, AM, 2004, Facet Joint Kinematics and Injury Mechanisms During Simulated Whiplash, Spine, Lippincott Williams & Wilkins pub. 29(4):390-397
- []Quiring, DP, 1947, The Head, Neck, and Trunk. Muscles and Motor Points. Lea & Febiger, Philadelphia, 1947.
- []SAE, 1986, "Human Tolerance to Impact Conditions as Related to Motor Vehicle Design," July 1986, SAE J885, the Society of Automotive Engineers.
- []Severy DM, et al., 1955, Controlled automobile rear end collisions - an investigation of related engineering and medical phenomena. Canadian Services Medical Journal, pages 727-759, 1955.
- []van der Horst MJ, 2002, Human Head Neck Response in Frontal, Lateral and Real End Impact Loading: modelling and validation. PhD. Thesis: Technical University of Eindhoven, 2002.
- []Winters, JM, et al., 1988, Estimated mechanical properties of synergistic muscles involved in movements of a variety of human joints. Journal of Biomechanics, 21:1027-1041, 1988.
- []Winters, JM, et al., 1985, Analysis of fundamental human movement patterns through the use of in-depth antagonistic muscle models. IEEE Transactions on Biomedical Engineering, BME-32:826-839, 1985.
- []Wismans, JSHM, 2000, Reduction of neck injuries and their societal costs in rear end collisions. In First European Vehicle Passive Safety Network Conference, 2000.
- []Yoganandan, N, 1998, Biomechanical assessment of human cervical spine ligaments. In Proceedings of the 42nd Stapp Car Crash Conference, pages 223-236. Society of Automotive Engineers, 1998. SAE Paper No. 983159.
- []Yoganandan N, et al., 2001, Biomechanics of the cervical spine Part 2. Cervical spine soft tissue responses and biomechanical modeling. Clin Biomech (Bristol, Avon) 2001;16:1-27.
- []Zajac, FE, 1989, Muscle and tendon: properties, models, scaling, and application to biomechanics and motor control. CRC Critical Reviews in Biomedical Engineering, 17:359-411, 1989.
SOFTWARE
LifeMOD
We would like to announce a powerful new release of LifeMOD. This release was developed as part of our long-term modeling strategy and with close cooperation from commercial clients and our university consortium. The user interface has been completely restructured and has been reorganized with libraries for motion capture data sets, models, postures, environments, contact conditions, etc. We have also expanded our muscle modeling capability to include Hill type muscles in addition to our LifeMOD trainable muscle elements. There is a muscle wrapping tool which can model accurate lines of action as muscles wrap and slide around structures. We have included ergonomic features such as vision cones and body center-of-mass reporting. Expanded the self-training tutorials include a tennis player, grasping hand and detailed whiplash model (featured in this newsletter). This functionality is in addition to many convenience features that you will see in the program.
LifeMOD/KneeSIM
We would like to introduce a new version of
LifeMOD/KneeSIM,
a complete virtual product development solution for Total Knee
Replacement Systems. The product, developed in collaboration with the
world's leading orthopedic companies, can be used for in vivo
simulation to ensure proper tibial rotation, validate femoral rollback,
minimize patella shear, maximize quadriceps efficiency and increase
durability and design robustness. LifeMOD/KneeSIM has proven itself in
the design of PCL/ACL sacrificing/retaining and fixed/mobile bearing
component systems. With simulation times of less than five minutes,
hundreds of design iterations may be characterized in a day. With this
powerful tool, engineers gain insight into cause and effect
relationships between design changes and response in the body.
See case study.
See press release.
LifeMOD/NeckSIM
We would also like to introduce a new product, LifeMOD/NeckSIM, a
complete detailed cervical spine modeling tool. LifeMOD/NeckSIM is a
plug-in to the main LifeMOD program offering the incorporation
of a detailed cervical spine model in a full body LifeMOD model.
LifeMOD/NeckSIM automates the vertebrae discretization, disk force
generation and soft tissue generation. The muscles may be either
Hill-type or trainable LifeMOD elements. Complete with the new tissue
wrapping feature, accurate lines of action may also be represented in
the spine model. This tool has great utility with applications in
injury, safety, orthopedics, surgical simulation, etc.
See case study.
Learn more by visiting our web page or by contacting us at newsletter@lifemodeler.com.
SERVICES
The Biomechanics Research Group, Inc. is a service-based organization with many major commercial successes using LifeMOD human simulation in the design process. We are expert in the development of the appropriate models, simulation cases and human response signature development to accelerate innovation of your product and greatly reduce the time to market. Contact us to see how we have done this in many industries.
OTHER NEWS
LifeMOD/KneeSIM
To replicate normal knee function, Smith & Nephew conducted
in-depth analyses of natural knee kinematics and the inherent
limitations in knee replacement systems.
LifeMOD/KneeSIM played a key role in
this investigation. "We chose to partner with BRG because of their experience,
technology, and expertise in the area of applying virtual product development
engineering to human activity," states Brian McKinnon, one of the
lead engineers on the Journey Knee Program. This effort led to the
innovative JOURNEY anatomical knee system designed to move and feel
like a normal knee, and addresses problems still found in conventional
systems such as instability and limited flexion. The new Journey Knee
System was voted the
"Best in Show" at the 2006 AAOS meeting in Chicago last year.
See press release.
ORL
This month we are excited to announce the expansion of our partnership with the
Orthopaedic Research Laboratories, in Cleveland Ohio,
under the direction of A. Seth Greenwald, D. Phil (Oxon). In addition to using
LifeMOD/KneeSIM as a basis
for comparative studies between commercially available total knee replacement systems,
they have chosen LifeMOD/NeckSIM
as a basis of comparative studies for spinal devices. These capabilities will complement
their existing efforts to provide functional performance data to a significant number
of national and international manufacturers, the Food and Drug Administration (FDA) and the
orthopaedic surgeon community. All these efforts are directed toward an optimization of
surgical techniques, orthopaedic devices and surgeon education to improve patient outcome.
Partners
To respond to the ever-growing LifeMOD community we have developed partnerships with several
more full service resellers across the world including:
- China --- Zhongtian-Noah Sports Science Co. Ltd.
- France --- INCAT France
- Germany --- VI-Grade, LLC
- Greece --- O Vision 2000 S.A.
- India --- CSM Software Private Ltd.
- Italy --- Lista Studio, SRL
- Japan --- Inter-Reha CO., Ltd.
- Japan --- Nihon VI-Grade
- Korea --- AhTTi
- Netherlands --- SayField International
- Romania --- Magic Engineering, SRL
- South Africa --- MSC-Africa Simulating Reality (Pty), Ltd.
- Spain --- Analisis y Simulacion S.L.
- Taiwan --- Taiwan Auto-Design Co.
- Thailand --- Sigma Solutions Co., Ltd.
- Turkey --- Bias Muhendislik/Engineering
- UAE --- Nezmin Trading
- UK --- Marlbrook, Ltd.
- USA --- Diverse Solutions, Inc.
- USA --- ESA Corp.
Referral Network
Throughout the years, we have received many employment inquiries from
student graduates, and professionals seeking employment to utilize
their skills with LifeMOD. Also, we have been repeatedly asked for
references by our top industry clients for LifeMOD-trained talent. We
have decided to combine both these needs in the LifeMOD Employment
Referral Network. If you are a LifeMOD trained investigator or an
industry professional in need of a LifeMOD trained investigator please
contact us.
New Publications
New Publication: "Optimizing Total Knee Replacement Kinematics", Ryan Willing, Il Yong Kim, Ontario Biomechanics Conference , March 9-11, 2007, Barrie, Ontario, Canada,
Abstract
New Publication: "Advanced Computational Modeling of Ejection Scenarios", Graham Joyce, 44th Annual SAFE Symposium, October 23-25, Reno, Nevada, See PDF
New Publication: "Biomechanics modeling of human musculoskeletal system using a multibody dynamics package", A. Veloso, G. Esteves, S. Silva, C. Ferreira, F. Brandão, International Association Of Science And Technology For Development, Proceedings of the 24th IASTED international conference on Biomedical engineering, Innsbruck, Austria, Pages: 401 - 407. See PDF
New Publication: "Biomechanical Modelling of a Golf Swing by Means of the Multibody-Kinetics Software ADAMS", Betzler, N., Hofmann, M., Shan, G., Witte, K., International Journal of Computer Science in Sport, Volume 5/Edition 2, Abstract.
New Publication: "Modelling with BRG.LifeMOD in Sport Science", Hofmann, M., Dänhardt, M., Betzler, N., Witte, K., Edelmann-Nusser, J., International Journal of Computer Science in Sport, Volume 5/Edition 2, See PDF.
New Publication: "Validation of a full-body computer simulation of the golf drive for clubs of differing length", Kenny, I.C., Wallace, E.S., Brown, D. and Otto, S.R., The Engineering of Sport 6, Volume 2: Development for Disciplines, See PDF
New Publication: "Development of a full-body computer model for golf biomechanics", Kenny, I.C., Wallace, E.S., Brown, D. and Otto, S.R., Annual Conference of the Exercise and Sport Sciences Association of Ireland, See PDF
New Publication: "The Effects of Racket Inertia Tensor on Elbow Loadings and Racket Behavior for Central and Eccentric Impacts", Steven M. Nesbit, Michael Elzinga, Catherine Herchenroder and Monika Serrano, Journal of Sports Science and Medicine, Vol 5, Issue 2, 2006, See PDF
If you would like further information on our software and services, please give us a call.
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