$54 Journal of Biomechanics 2006, Vol. 39 (Suppl 1)

5621 Th, 09:30-09:45 (P37) Criteria for optimality in movements A. Eriksson. KTH Mechanics, Stockholm, Sweden

A general algorithm, based on a temporal finite element interpolation of displacements and controls, was developed for the evaluation of optimal move- ments between initial and final configurations. The algorithm, primarily aimed at musculoskeletal movement simulations, was found efficient and reliable, even for complicated dynamic formulations, [1]. The result from the algorithm is the configuration as function of time, but also the set of a priori unknown control forces needed to create the desired motion. With sufficient freedom in the description of the control forces, they are chosen to optimize some measure of the movement or the controls. A common criterion is to minimize the forces needed to produce the movement. Another interesting possibility is to seek the smoothest movement. Methods for minimization of either jerks or accelerations, following an idea by Flash and Hogan, [2], were introduced in the algorithm. Examples of limb movement indicate that the introduced optimization criteria strongly influence the obtained solutions. This observation is independent of whether the muscular forces are seen as a redundant set of individual forces, or are summed to resultant forces or moments at the considered joints. The presentation describes the developed algorithm, the studied optimization criteria, and the conclusions from a set of examples concerned with bio- mechanical targeted movement.

References [1] A. Eriksson. Analysis methodology based on temporal FEM for bio-mechanical

simulations. In: M. Ursino, C.A. Brebbia, G. Pontrelli, E. Magosso (Eds.), Modelling in Medicine and Biology VI. 2005; WIT Press, Southampton.

[2] T. Flash, N. Hogan. The coordination of arm movements: an experimentally confirmed mathematical model. J. Neurosci. 1985; 5: 1688-1703.

5286 Th, 11:00-11:15 (P40) Effect of different walking speed on plantar pressure during heel strike to mid-stance phase - 3D dynamic finite element analysis S.-C. Lin 1,2, W.-P. Chen 1 , C.-W. Yeh 1 , J.-H. Lin 1 , F.-T. Tang 2. 1Department of Biomedical Engineering, Chung Yuan Christian University, Taoyuan, Taiwan, 2Department of Rehabilitation Medicine, Chang Gung Memorial Hospital, Taoyuan, Taiwan

In previous literature that used finite element (rE) method to study the foot biomechanics are mostly static or quasi-static analyses and dynamic analyses are rare. The purpose of this study was to develop a 3D FE foot model in order to investigate the effect of walking speed on the plantar pressures (PP) from heel strike (HS) to foot flat (FF) in the stance phase of gait using 3D dynamic FE analysis. In this research, a 3D hexahedral FE model of left foot including bones, cartilages, and soft tissues was developed. Besides, three FE models of footwear including flat insole, total contact insole, and flat insole combined heel pad were also established, respectively. Three materials of insoles, such as plastazote, blue plastazote and pink plastazote were chosen. In addition, the kinematic gait data of a normal male subject measured in three walking velocities (Fv = 1.79, Nv = 1.55 and Sv = 1.09 m/s) were used to set the boundary conditions of the FE models. The simulation results were validated with the vertical ground reaction force that measured in gait analysis. Results showed that walking with fast velocity would result in higher PP at the lateral and medial heel. The peak PP at the lateral heel was 374, 356, and 261 KPa as well as medial heel was 340, 322, and 219 KPa while walking with Fv, Nv, and Sv velocities, respectively. In addition, the flat insole combined heel pad with pink plastazote had better effect in reducing peak PP during HS phase. The 3D hexahedral FE model of a left foot developed in this research may provide useful information for footwear design and other foot biomechanics applications. With the application of this model, dynamic FE analysis for a full gait cycle can be completed in future studies.

6886 Th, 11:15-11:30 (P40) Li feMOD modelling of a complete human body: a walk with a right knee varus and valgus movement G. Agnesina, R. Taiar. Laboratoire d'Analyse des Contraintes M~caniques (LACM - EA 3304), UFR STAPS, Universit6 de Reims, France

Objective: Postural adjustments and muscular contributions of a complete human body are studied during a walking task with a right knee varus and valgus movement. The model used in our study will give us the comprehension of the muscle coordination in the aim to anticipate injuries during movement. Methods: A healthy subject was chosen with the following physical conditions: a man, 24 years old, 1.88 m height and 77 kg weight. A motion analysis system (6 cameras Vicon MX3) and a force plate (AMTI OR6-7-2000) were used to collect kinematic and kinetic data. We imported the motion data and we created the human model (19 segments and 118 muscles) in MSC ADAMS - BRG LifeMOD 2005 software. The physiological cross sectional area of muscles (pCSA) has been used to calculate muscle forces.

Oral Presentations

Results: The different angles (knee, lumbar, thoracic . . . . ) and muscular tensions were calculated during Varus and Valgus movement. We showed that Lower-neck and Lumbar angle are in the same direction in the frontal plane with max values larger in the Valgus movement. According to the movement, the thoracic angle takes opposite values (amplitude +70 for the varus and of -300 for the valgus). On the other hand, it was observed that medial muscle tensions decrease followed the varus movement as compared with the valgus movement. Conclusions: The originality of our study is to take for the first time into account several muscles in these movements of varus-valgus to know the global coordination. The results are in good agreement with other studies covering the subject. We also could validate our model thanks to the force plate. The average deviation is of 18.08±12.91 Newton between LifeMOD software and the force plate values.

5270 Th, 11:30-11:45 (P40) Biomechanical evaluation of using iliac bone or rib bone graft in anterior t12-11 interbody fusion and effect of triangulation of the anterior fixation screws C.-H. Chien 1,3, W.-P. Chen 1, T.-J. Huang 2, C.-'~ Lin 1. 1Department of Biomedical Engineering, Chung Yuan Christian University, Taiwan, 2Department of Orthopaedic Surgery, Chang Gung Memorial Hospital, Taiwan, 3Department of Orthopaedic Surgery, Ten-Chen General Hospital, Taiwan

In spinal fusion surgery, bone grafts are commonly used to enhance bone fusion and to provide stability. In anterior approach of thoracic-lumbar vertebral surgery, the ribs are often resected and may be an alternative choice for bone graft besides iliac bone. The purpose of this study was to use a validated finite element model to evaluate the effects of different sources of bone graft in the interbody thoracic-lumbar spinal fusion surgery. Besides, we evaluated the effects of triangulation of the double-screw fixation and the cortex penetration of the screw. CT images of a T12-L1 motion segment of a healthy young male were obtained to create the intact T12-L1 finite element model. Three types of bone grafts, iliac crest, one-rib and two-rib were used. Two-level anterior instrumentation with/without triangulations of the double-screw on the same level and with/without penetration of the screws was compared. Couple forces of 10 N-M moments were given for simulating flexion, extension, rotation and lateral bending moments combined with 300 N compression pre- load were imposed on the rigid plate on the T12 upper endplate for each condition, respectively. The von Mises stress distributions for the bone grafts were calculated. According to our results, the stresses on the two-rib and iliac bone grafts were similar. There was stress concentration on the one-rib graft. Under the condition of solid fusion, two-rib bone graft can be the alternative choice of bone graft material. Both triangulations of the anterior vertebral screws of the same level and penetration of screws to the opposite cortex can facilitate the fixation in anterior spinal fixation. Triangulations between the screws of the same level can be an attractive alternative way to facilitate the stability in anterior spinal instrumentation avoiding the potential risks of cortical penetration.

4591 Th, 11:45-12:00 (P40) Mandibular advancement devices design and impact on TMJ articulation: a rigid element model analysis

L. Ch~ze. University Lyon 1, Lyon, France

Objectives: Understand mechanical forces applied by two different designs of Mandibular advancement devices on the TMJ articulation. Design: Comparative study of traction based vs. compression based MAD on a model of the TMJ articulation. Methods: Rigid elements model with mandible in a 10 mm protrusion position was developed. The ATM is described by temporary perfect contact on a plane that represents the temporal slope. The following muscles are considered: masseter, medial pterygoid, lateral pterygoid, anterior temporal, posterior temporal and opener muscles. Static equilibrium can be written as hyperstatic equations and resolution is obtained through numeric optimization of different criteria under constraints. Sum of muscle forces ( ~ Fm), sum of muscular constraints [~(Fm/A)2], and articulation contact strength (Ro) are the criteria for our study. Results: For MAD-1 (compression based), equation results show that impor- tant strength is applied in the masseter (12.6 to 16.2 N) and posterior temporal (69.9N). As both muscles lift the mandible up, this implies mouth opening happens when these muscles are at rest. However MAD-2 (traction based) enables 10 mm protrusion with minimal effort on these muscles respectively 0.9 to 1.1 N for masseter and 1.7 N for posterior temporal. Additionally, TMJ contact strength is consistently less with MAD-2 than with MAD-1 [39 vs. 43.1 ( ~ Fm); 43.7 vs. 47.9 (~(Fm/A)2); 36.8 vs. 40.8 (Ro)].