Influence of geometrical personalization on the simulation of clavicle fractures.

Finite element body models enable the evaluation of car occupant protection. In general, these models represent average males and inter-individual geometry variability is not taken into account. As the most frequent shoulder injury during car lateral accidents is a clavicle fracture, the purpose of this study is to investigate whether clavicle geometry has an influence on bone response until failure, and whether geometrical personalization of clavicle models is required. Eighteen clavicles from 9 subjects (5 males and 4 females, mean age: 76 +/- 12 years) were harvested. Six clavicles were scanned, enabling the development of subject-specific models and the quantification of geometrical features defining shape and cortical thickness. Bone mineral densities (BMD) were measured through double X-ray absorptiometry. Then, the general clavicle responses to dynamic compression until failure were studied. Simulations of the compression tests were carried out with the subject-specific models to assess the sensitivity of force-deflection clavicle responses to geometrical features. Clavicle fractures occurred at an average velocity of 1.41 +/- 0.4 ms(-1), with a fracture force of 1.48 +/- 0.46 kN and a deflection of 5.4 +/- 1.1 mm. A significant difference was found between male and female clavicle force values at rupture although their BMDs were not significantly different. Simulations with subject-specific models led to the conclusion that cortical bone thickness and bone shape have large effects on bone responses until failure and on fracture location. This study highlights the need for a geometrical personalization of clavicle models in order to take into account both gender discrepancies concerning clavicle shape and aging effects affecting cortical thickness.