ADVANCED LOWER LIMBS MODEL WITH RADIOSS

APPLICATION TO FRONTAL AND LATERAL IMPACTS

P.J. Arnoux

1, 2, L.Thollon

1, 2, K. Kayvantash

1, C. Cavallero

2, C. Brunet

2.

1 MECALOG - Safety Business Unit, Paris, France. 2 Laboratoire de Biomécanique Appliquée, URMRT 24 Faculté de Médecine - INRETS, Université de

la Méditerranée, Marseille, France. KEY WORDS : BIOMECHANICS, FINITE ELEMENT METHOD, LEGS, WITHIN SHOCKS BIOMECCHANICS, the knee and the lower leg are highly subjected to damage and failure. In order to investigate these injuries mechanisms and improve protection of lower limbs, the Lower Limb Model for Safety has been designed. The aim of this development was to set an injury model based on an accurate description of all anatomical parts of the lower limb. MODEL DESCRIPTION Geometry data was based on more than 500 CT-scan and MRI slices of the same lower limb specimen. The compact and spongious bones were considered as elastoplastic shells and solid materials and include the distribution of density ands thickness along the bone. The soft tissues (all ligaments, knee cartilage, menisci, capsula and shape of muscle mass) which contribute to the joint stability and compliance were described using viscoelastic and elastic elements (springs, shells and solids). At last, surrounding tissues were modelled with viscoelastic solid and elastoplastic membrane elements for skin (cf. fig. 1) (Beillas and Arnoux 2001).

Fig. 1 – View of ligamentous LLMS knee joint, whole model overview, complete knee joint with capsula view and knee open view (without capsula, muscles and distal femoral bone component) MODEL VALIDATION The model validation focused on four aspects : 1. The mechanical properties of isolated tissues were mainly evaluated on the bases of tensile traction test on soft tissues (Arnoux 2000, Johnson 1994, Haut 1990), and three point bending test for long bones (Beillas 1999). 2. The second level deals with an evaluation of the model capability by anatomists in order to give a detailed description of physiological movements (mainly in flexion cf. figure 2).

Fig. 2 - Three stage of the knee during physiological flexion

3. The third validation level deals with sub segment testing according to available literature data (Parenteau 1996, Hayashi 1996) and concerns dynamic and static ankle foot compression test, knee impact test (cf. Hayashi impact test reported in figure 3) for which the model validation was performed by comparison of force time experimental data. For three point bending test, inversion and dorsiflexion test model, the validation was achieved on moment versus time recorded data.

Fig. 3 - Force versus time force and Von Mises distribution on bone component in case Hayashi impact test. For this test the load is applied with a 20Kg mass cylindrical impactor with a 4.94m/s initial velocity. 4. The complete model validation was obtained using frontal and lateral crash situations. For frontal validation a sled test was performed using the coupling of LLMS model to HybridIII dummy model (Beillas & Arnoux 2001). In the lateral impact situations such pedestrian impact tests, validation was achieved through to loading case: complete leg shearing and bending were performed on the lower leg (Kajzer and Cavallero 1990, 1993) (fig. 4 illustrate Kajzer and Cavallero bending test ).

Fig. 4 - LLMS model validation in the case of a lateral bending test. The two firsts figure show model boundary condition (the thigh is fixed, and load occurred with a 40Kg impactor with an initial velocity of 20 Km/h. The last view show Von Mises stress distribution on knee joint. DISCUSSION - CONCLUSION The results show the ability of the model to describe knee leg kinematics during shock i. e. the leg bending and also the shearing effects between tibia and femur. Force evolution curve and stress localisation at impact were in good agreements with experimental measurements and observed injuries. The Radioss lower Limb model for Safety (LLMS) is know available and

was validated in the context of physiological movements, frontal and lateral impacts. The accurate description of anatomical parts ensures a wide range of use in the context of shock biomechanics and biomedical applications. ACKNOWLEDGMENT The LLMS project was performed in collaboration with people form Mecalog company, Laboratory of Applied Biomechanics (INRETS-Univ. Med. – Marseille) and Wayne State. We would like to acknowledge the contribution of all partners to this project. REFERENCES Arnoux P. J., Modélisation des ligaments des membres porteurs : A propos des ligaments du genou. Thèse de Doctorat de l’Université de la Méditerranée (Aix-Marseille II) en Mécanique, 03-03-2000.

Arnoux P. J., Thollon L., Kayvantash, The Radioss lower limb model for safety – Guideline– Janvier 2001 Beillas P.. Modélisation des membres inférieurs en situation de choc automobile. PhD thesis, École Nationale Supérieure d'Arts et Métiers, Paris, France, 1999.

Beillas P. J., Arnoux P. J., Brunet C., Begeman P., Cavallero C., Yang K., King A. Kang H. S., Kayvantash K. Prasad P., Lower Limb: Advanced FE Model and New Experimental Data, International Journal of STAPP - ASME , 2001, vol. 45, pp. 469-493

Hayashi, S., Choi, H.-Y., Levine, R.S., Yang, K.H., and King, A.I., Experimental and analytical study of knee fracture mechanisms in a frontal knee impact, in 40th Stapp Car Crash Conference Proc. 1996. p. 161.

Kajzer J., Cavallero C., Bonnoit J., Morjane A., Ghanouchi S., Response of the knee joint in lateral impact: Effect of bending moment. Proc. IRCOBI, pp. 105-116, 1993

Kajzer J., Cavallero C., Bonnoit J., Morjane A., Ghanouchi S., Response of the knee joint in lateral impact: Effect of shearing loads. Proc. IRCOBY, pp. 293-304, 1990

Nyquist G.W., Cheng R., El-Bohy A.R., and A.I. King. Tibia bending : strength and response. In 29th Stapp Car Crash Conference Proc., n. 851728, pages 99--112. SAE, 1985.

Parenteau C. S., Foot and Ankle joint response – epidemiology, biomecanics and mathematical modeling, Ph. D. thesis, Chalmers Univ. 1996.