In vitro evaluation of a malleus head to stapes head 'incus replica' prosthesis.

An ossicular prosthesis produced by making a mould from a cadaveric incus and injecting ionomeric cement into it (incus replica prosthesis, IRP) has been cemented to the malleus head and stapes head and evaluated in fresh human temporal bones using a laser vibrometer. Stapes velocity was recorded under acoustic stimulation and foot plate displacements were derived. Fourteen frequencies between 125 Hz and 8000 Hz have been used. Measurements were made with the ossicular chain intact, following removal of the incus, with the prosthesis cemented to the malleus, but not the stapes, and with the incudo-stapedial joint cemented. In a second series of experiments the performance of the IRP was compared with that of a Causse partial ossicular replacement prosthesis, using the same experimental set-up. The results indicate that the prosthesis performs almost as well as the intact ossicular chain and that cementing the incudo-stapedial joint gives better sound transmission than leaving it uncemented. In addition the IRP outperforms the conventional partial ossicular replacement prosthesis.