Influence of the shape and material on the behaviour of a total ossicular replacement prosthesis

To study the influence of the shape and the material on the behaviour of a total ossicular replacement prosthesis (TORP).

It was hypothesized that the influence of the shape and material of a TORP on its performance could be quantified using a simple mechanical model. The prosthesis is represented simply by an axisymmetric shape and two models are used. In the first model, we assume that the strain of the prosthesis is negligible, whereas the strain is taken into account in the second model. In both cases, literature plots of stapes displacement versus frequency are used to check the validity of the modelling.

It was found that the influence of the strain of the implant was insignificant in comparison to its rigid body movement. Furthermore, if it is assumed that the reaction force exerted by the inner ear on the stapedial footplate depends on both frequency and mass, it can be shown that the human body is able to adapt itself to the mass and shape of the prosthesis.

As the prosthesis is not strained and no material criteria appear in the equation used in the modelling, both materials studied, titanium and hydroxyapatite, are equivalent from a mechanical point of view. In addition, a cylindrical prosthesis would give good results in response to an external stimulus but its very rigidity could damage the inner ear during pressure shocks.