OPTIMAL DESIGN OF A TRAPEZO-METACARPAL PROSTHETIC IMPLANT

OBJECTIVE : Investigating the causes of the damage and progressive pathologies after an arthroplasty of the trapezium-metacarpal articulation (in the basis of the thumb) and optimizing the design of the prosthetic implant. MATERIALS AND METHODS : Based on Dr Ledoux's prosthesis as a model in this study and developping an evolutionary 3D finite element model with ABAQUS program taking into account « the stress shielding » phenomena, the bone neoformation and the bone lysis and based on the stimulus concept and the wolf's law, the damage has been investigated as it is due to the high difference of stiffness between Titanium material of the implant and both of cortical and trabecular bones. RESULTS : It was shown that a significant improvement of the lifetime of the implanted metacarpal bone could be obtained with a special implant made, along its length, of different slices of hypothetic homogenous titanium material with decreasing Young modulus. Of course, the study was a first approach and additional more advanced optimizations remain necessary to improve the actual results. CONCLUSION : The interest of an intelligent material with a functionally graded young modulus is now established. The possibilities to create such a material are : - Powder metallurgy by mixing titanium powder and less stiff inclusion before shaping the implant. - EBM process (electron beam melting) of the Arcam company and now tested by SIRIS. These two techniques seem to be very attractive but need complementary studies of feasibility. Industrial partners specially small and medium size companies should be welcome. POTENTIAL APPLICATIONS AND KEY BENEFITS : The concept of 'an intelligent biocompatible material' in the form of a graded titanium young modulus allowing adaptation of local stiffness at any point of the implant ,was brought to light in the context of studying the trapezo-metacarpal implant, but this concept can be extended to different types of prosthesis (hip prosthesis,...) in order to lengthen their lifetime.