Clavicle fracture analysis
One of the interesting uses of musculoskeletal simulation is to assess the forces and moments acting across a bone fracture. Knowledge of these loads is of crucial importance to designers of bone fixation devices as well as to the surgeons using them. John Rasmussen presented a paper on this idea co-authored with Australians Paul Taylor and Karl Stoffel at the recent Pre-ORS symposium on computer simulation in orthopaedics. The above picture shows an imagined position of a midshaft clavicle fracture. It is obvious that the bone is loaded by a multitude of muscle forces and the corresponding joint reactions at the bone’s end supports on the sternum and scapula respectively.
The idea behind the simulation is that a rigid joint is introduced in the model at the location of the fracture. The rigid joint does not change the mechanics, but it measures the forces and moments transferred across it. These forces and moments are what the bone fixation device and attachment strategy must subsequently be designed to carry until the bone has healed. Alternatively the model can be used to investigate whether the loads can be controlled in the healing period by temporary paralysis of selected muscles. New version of the C3D-to-AnyScript converter A new version of the C3D-to-AnyScript converter (c3d2any) is now available for download here. In previous versions only kinematical drivers were automatically created for those data points that were certain to have been measured. This was based on the content of the camera and mask bytes in the C3D file. However, this sometimes meant that not all (or any at all) drivers were created. This has now been changed such that kinematical drivers are created for all points, but these are split into two files: <output filename>.MarkerListMover.any and <output filename>.ProcessedListMover.any. In the main file, the <output filename>.ProcessedListMover.any is commented out per default. As mensioned in message #1650, C3D files without an ANALOG or POINTS section could not be converted in earlier versions. This has now been fixed by Michael Skipper Andersen who also made the previous versions. Feedback, bug reports or feature requests are still very welcome
Upcoming webcast - 22 May: Simulating the dynamic muscle force in an index finger during tapping
Speaker: John Z Wu, Ph.D., National Institute for Occupational Safety and Health, Morgantown, WV, USA.
Many previous webcasts are available for download and replay here. Tips and tricks #13: Penetrations errorsMany muscles in the body are wrapped over bones and slide on the bony surfaces when the body moves. This means that the contact forces between the bone and the muscle are always perpendicular to the bone surface, and the muscle may in fact release the contact with the bone and resume the contact later depending on the movement of the body. Via point muscles are not capable of modeling this type of situation, so the AnyBody Modeling System has a special muscle object for this purpose.
A wrapping muscle is presumed to have an origin and an insertion just like the via point muscle. However, instead of interior via points it passes a set of surfaces. If the surfaces are blocking the way then the muscle finds the shortest geodesic path around the surface. Hence the name of the class: AnyShortestPathMuscle. The fact that the muscle always uses the shortest path means that it slides effortlessly on the surfaces, and hence there is no friction between the muscle and the surface.
Sometimes one or some of the points defining a muscle turn out to be located inside one of the surfaces that the muscle can wrap on. In general this should be avoided because a part of the muscle path will be located inside the surface and this part of the path becomes unpredictable.
The penetration errors can occur at different times:
1. They may happen at load time when the model is in its initial position. If they only occur in this position they are not important. It just means the initial posture creates penetration.
2. They may occur when running inverse analysis of the model. This can be important.
There can be different reasons for this, including:
1. If for example the arm is penetrating the thorax this may give a penetration warning. This is not an error related to the Body model but related to the way the model is being used. Here the remedy is to change the drivers of the model.
2. In principle all surfaces in the model used for wrapping have been made in a way that makes them scale with the model. When defining a cylinder it is typically defined using three nodes. These nodes control the size and location of the cylinder. When the bone is scaled, these control nodes will also be scaled like any other node on the bone and consequently the cylinder will be scaled too. Ellipsoids are made in a similar way. This setup does not guarantee that penetration errors will never occur. If the via point and the surface are located on the same bone and are very close, different types of scaling and sizes could potentially create penetration errors.
In general the remedy is to
1. Exclude all muscles from the model except the one causing the problem.
2. Insert an AnyDrawParamSurface in the surface being penetrated to visualize it you can do this directly in the muscle. Typically by writing Surf1={ AnyDrawParamSurf drw={}; }; //assuming a Surf1 reference is existing!
3. Insert an AnyDrawRefFrame in the node which is penetrating.
4. Try to understand the root of the problem, whether it is related to scaling or motion.
5. Do modifications on either model or motion to solve the problem | | AnyBody publicationsPaul Taylor, Karl Stoffel and John Rasmussen: A Computational Model of Clavicle Fracture Fixation. 16th Annual Symposium on Computational Methods in Orthopedic Biomechanics. University of California at San Francisco, March 1, 2008. J. Holmberg (2008): Computational Biomechanics in Cross‐country Skiing. Licentiate thesis, Linköping University (Sweden), Dept. of Management and Engineering. Abstract and fulltext. 
Click to view an animation of Holmberg's cross-country skiing model
Mark de Zee, Deborah Falla, Dario Farina and John Rasmussen (2008): Simulation of pain-induced alterations in cervical motor control. World Congress on Neck Pain. January 20 - 22, Los Angeles, California, USA. Resellers appointed for Italy, Spain, and PortugalAnyBody Technology works towards establishing a global network of partners reselling our technology. Our objective is to find partners sharing our view that the reseller over time will evolve to become a local partner for AnyBody clients in his region with respect to training, support, and consulting assistance.
We welcome our new partners, AperioTec in Spain covering the Iberian peninsula for us, and EnginSoft in Italy (covering Italy). Please feel free to contact us or your local AnyBody representative at your discretion. Seminar in Sunnyvale, CA:
Medical Device Implant SimulationOzen Engineering, our partner in California, invites you to a seminar on April 7th. During this event Ozen Engineering will demonstrate how the powerful combination of AnyBody and ANSYS finite element modeling enables realistic analyses of medical device implants.
The seminar is free of charge and is scheduled to take place from 12:00PM to 2:00PM.
View the invitation and register here. Seminar in Barcelona, SpainOn 10 April 2008 AperioTec, our partner in Spain, and AnyBody Technology will organize a presentation on AnyBody.
The presentation will take place at the Hotel Hespería Sant Just; c/ Frederic Mompou 1; 08960 Sant Just Desvern that is on the outskirts of Barcelona (close to airport, easy travel by car, tram).
The seminar is free of charge and is scheduled to take place from 09:00 to 13:00.
Click here for further information
Events: Meet AnyBody at...2008 Digital Human Modeling for Design and Engineering Conference and Exhibition, June 17-19, Pittsburgh, PA
ASME SBC2008, June 25-29, Marco Island, FL
ESB2008, July 6-9, Lucerne, Switzerland
NACOB 2008, August 5-9, Ann Arbor, MI, U.S.A. AnyBody at the Innovative Seating Conference...A few weeks ago in Frankfurt am Main, Germany, Prof. John Rasmussen conducted a 3 hours seminar on Simulating (dis)comfort: The AnyBody project.
View his presentation here. AnyBody at the ORS…This year’s annual meeting of the Orthopaedic Research Society took place in San Francisco, March 1-4, 2008. At Saturday’s pre-ORS meeting, John Rasmussen presented work (described above) on estimating the in-vivo forces in the clavicle following fracture fixation.
Sunday through Tuesday, AnyBody Technology exhibited in the Moscone West Convention Center, downtown San Francisco. Surrounded by nearly 2,000 posters our exhibit attracted lot of attention during the poster sessions, let alone the coffee and snack breaks.
We are looking forward to elaborating on friendships and relations established at the ORS. We hope for another interesting event in Las Vegas next year! Meet an AnyBuddy: Mark de ZeeMark de Zee, 36, is a co-founder of AnyBody. Mark a biomedical engineer specialized in biomechanics and musculoskeletal modeling. His main research interest is to develop, validate and apply musculoskeletal models to basic research, clinical problems and sport science.
Mark’s work is taking place in the Department of Health Science and Technology at Aalborg University, where he operates as a Research Assistant Professor. His latest projects concern the development and validation of a neck model, as well as the biomechanical analysis of prosthetic discs in the lumbar spine.
Mark is very active in sports. He is fond of mountainbiking, bicycle racing, and speed skating. Mark is a Dutch citizen, but has lived in Denmark for many years. He is married, has 2 kids and a big yellow cat that is often mistaken for a cougar. He lives in the same suburbian village one mile from the office as Michael Damsgaard and Arne Kiis – 3 family guys rockin’ the neighborhood. - - - o o o - - -
Sincerely
The AnyBody Team. As usual, if you have news, questions or comments, please do not hesitate to contact us. |
