Inverse-dynamic model of the hindlimb of the rat

Track 2. Musculoskeletal Mechanics-Joint ISB Track 4694 We-Th, no. 76 (P57) Modelling of the temporomandibular joint and assessment of the temporomandibular joint disc movement M. Fri~ov~ 1, Z. Hor~k 1, R. Jirman 2, S. KonviSkov~ 1. 1Laboratory ef

Biomechanics, Department of Mechanics, Faculty of Mechanical Engineering, CTU, Prague, Czech Republic, 2Department of Stomatology, 1st Medical Faculty, Charles University, Prague, Czech Republic The general purpose of this project is to develop a new complete replacement of the temporomandibular joint (TMJ). A three-dimensional model of the temporomandibular joint has been developed according to the CT and MRI data from the head of embalmed male cadaver showing no abnormalities. The task is symmetrical, therefore only a half skull and a half mandible were used. Next, the model consists of a temporomandibular (TM) joint disc, ligaments and muscles surrounding the joint. Movement of the temporomandibular joint disc during the jaw opening and closure is very sophisticated and it is not easy to observe it. In this project the movement was studied using magnetic resonance imaging FFE dynamic scan sequence with custom "spreader" device. We obtained several images in various positions inside the joint. These data were processed in CAD program and possible movement of TM joint disc was assessed. We intend to import this data into finite element model and perform finite element analysis where simple loading conditions will be set. It was proposed to use material properties, applied forces and boundary conditions from published data and solve the task as non-linear contact task. References [1] Donzelli RS., Gallo L.M., Spilker L.R., et al. Biphasic finite element simulation of the TMJ disc from in vivo kinematic and geometric measurement. Journal of Biomechanics 2004; 37: 42-48. [2] Nickel J.C., Iwasaki L.R., Walker R.D., et al. Human Masticatory Muscle Forces during Static Biting. Journal of Dental Research 2003; 82-3: 212-217. [3] Choi A.H., Ben-Nissan B., Conway R.C. Three-dimensional modelling and finite element analysis of the human mandible during occlusion. Australian Dental Journal 2005; 50(1): 42-48. 4955 We-Th, no. 77 (P57) 3D Parametrical mechanical modelling of femur F. Labesse-Jied 1, A. Pustoc'h 2, C. Joandel 1, L. Ch~ze 2. 1LaMI - UBP &

IFMA, University Clermont 2, Montlugon, France, 2LBMH, INRETS-UCBL, University Lyon 1, Lyon, France Introduction: Finite Element models are often used to study osteoporosis, prosthetic implants and surgical simulations. 3D reconstruction from medical images (CT scans, stereoradiography) is often used but this technique is quite invasive and expensive. This paper presents a 3D personalized parametrical model of femur based on simple geometrical and material parameters. It can be used to do comparative studies about mechanical bone performance under various loading conditions. Method: The model is built from 14 linear parameters and the neck/diaphysis angle. Meshing is automatic and parametered. The material properties are modelled to be linear elastic and isotropic. The material distribution is modelled as homogeneous throughout the femur (cortical and spongy parts). Results: Two load cases are applied (Viceconti et al. and Duda et al.) and results are compared to those obtained using the femur model from the Vakhum project. Analysis shows a better result approximation on the lateral femoral axis. Differences are more important for stress (20%) than for strain (9 to 16%). The load case including the abductors, ilio-tibial band and hip contact is performed at 45% gait cycle. Evolution of principal strains ~1 and ~3 and Von Mises stress '~VM along lines on the ventral and medial aspect of the human femur with Duda, Vakhum and parametrical models is similar. Discussion and Conclusion: To improve results, great trochanter geometry should be considered. Nevertheless, maximal error is 17.5%. This model allows interesting simulations or comparative studies. References M. Viceconti, et al. (1998). Medical Engineering & Physics 20: 1-10. G.N. Duda, et al. (1998). Journal of Biomechanics 31: 841446. http://www.u Ib.ac.be/projectJvakh um. 6805 We-Th, no. 78 (P57) Spinal force estimation from Non-Normalized EMG J.M.A. Visser 1,2, W.H.K. de Vries 1, C.T.M. Baten 1, J.H. van Die~n 3.

1Roessingh Research and Development, Enschede, The Netherlands, 2Structure and Motion Laboratory, Royal National Orthopaedic Hospital, Stanmore, UK, 3Institute for Fundamental and Clinical Human Movement Sciences, Faculty of Human Movement Sciences, Vrije Universiteit, Amsterdam, The Netherlands Spinal loading appears to play an important role in causation and provocation of low back pain. Monitoring spinal loading, therefore, is important in prevention

2.7 Musculoskeletal Modelling Meets Muscle Physiology

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and rehabilitation. The goal of this project was to develop a method for accurate estimation of spinal forces in an ambulatory situation. Spinal force estimation in the ambulatory measurement method (AMBER) was done using a moment distribution model. Current moment distribution methods depend on laboratory facilities for calibration. A novel moment distribution model based on recorded non-normalized EMG and trunk kinematics has been proposed. The EMG-muscle force relation is calibrated from a number of standardized field measurements by minimizing the difference between the muscle moment estimated by EMG and kinematics and the net moment obtained from upper body kinematics and known external loads. A minimal required calibration set was chosen from nine different calibration subsets. Because direct validation of the model on spinal forces is impossible, validation of the model was done by comparing estimated muscle moment and external moment. For symmetric lifting the estimated muscle moment compared to the external moment had a mean absolute error ~< 6% of the maximal external moment. For asymmetric lifting the mean absolute error for the moment estimation was ~< 12% of the maximum moment. These results are comparable with those from other EMG based moment distribution studies in the laboratory. The proposed spinal force estimation model gives a good spinal force estimation that is suitable for use in ambulatory situations. With improvements of the model real time ambulatory spinal force monitoring will become possible. 6290 Inverse-dynamic model of the hindlimb of the rat

We-Th, no. 79 (P57)

U. Wolfram 1, U. Simon 1, T. Henzler 1, P. Mail~er2, L. Claes 1. 1Institute ef

Orthopaedic Research and Biomechanics, University of UIm, Germany, 2Institute of Mechatronics at Chemnitz University of Technology, Chemnitz, Germany Introduction: Fracture healing experiments are increasingly performed on rats. Unfortunately, the musculo-skeletal loads in the hindlimb are not known. Nevertheless, these loads are essential for the proper design of these experiments. The study presents a numerical model to determine the muscle forces in the hindlimb during normal gait. An inverse-dynamics software (UFBSIM, [1,2]) was applied to perform the simulation. Methods: The hindlimb was modelled as a system of rigid bodies under the assumption of normal gait. The rigid bodies consisted of both bone and muscle mass. Mass properties were determined from CT gray-scale images. The muscles were modelled as massless vector chains spanning from insertion to origin over several deviating points. The gait analysis was performed using radiography images of a gait cycle of the rat. The ground reaction forces are taken from the literature [3]. The model was solved for the muscle forces using the inverse dynamics software including the application of an optimization criterion to solve the load distribution problem [1,2]. Results: The calculated muscle forces were compared to EMG data gained from the literature [4]. Muscles which served DOFs which were close to natural joints and not blocked showed good agreement in their activation time with the EMG data. The hip contact forces were predicted to be four times the body weight of the animal. Discussion: The hip contact forces seemed to be very high compared to other quadrupeds (sheep model [2]) which predicted these forces to be only about two times the body weight. However, the cross sectional area of the thigh in relation to the body mass of the rat is about nine times higher than for sheep. This indicates that the hindlimb of the rat is more muscular, hence, the higher hip contact forces are conceivable. References [1] Forster E., et al. J. Biomech 2004 [2] Forster E., et al. Proc CMBBE, Madrid, 2004. [3] Muir GD, et al. Exp. BrainRes. 1999. [4] Nicolopoulos-Stournaras S. J. Zool, 1984. 6776 We-Th, no. 80 (P57) Modeling the effect of seat height and fore-aft position on wheelchair propulsion L.-'~ Guo 2, K.D. Zhao 1, F.-C. Su 3, K.-N. An 1. 1Orthopedic Biomechanics Laboratory, Division of Orthopedic Research, Mayo Clinic Rochester, Rochester, MN, USA, 2Faculty of Sports Medicine, Kaohsiung Medical University, Kaohsiung, Taiwan, 3Institute of Biomedical Engineering, National Cheng Kung University, Tainan, Taiwan Handrim wheelchair propulsion is greatly affected by seat position. It is difficult to characterize the specific effects of seat position from experimental measurements alone, due to large inter- and intra-subject variability. Therefore, a mathematical model was created to better address this question. The model is a two-dimensional, four-bar linkage, static optimization model which maximizes the wheel progression moment given the subject-specific limits on the strengths