Design-Dependent Calculation of the Prosthesis Length in Malleostapedotomy.

OBJECTIVE: The results of a recently published micro-CT study suggested a correlation of the distance between long incus process and stapes footplate and the required prosthesis length in malleostapedotomy. The goal of this study was to test the reliability of that assumption. METHODS: Rectangular and bent prostheses were tested in 11 cadaveric human temporal bone specimens; 1 of them showed a stapedial artery. Prosthesis length was calculated based on the distance between long incus process and stapes footplate. The rate of acceptable prosthesis insertion into the vestibule was investigated. RESULTS: In both prostheses designs, the insertion depth into the vestibule did not exceed 1.0 mm. Two prostheses did not pass the footplate level in bent prostheses (18%) and 1 in rectangular prostheses (9%). CONCLUSION: A rough estimation of the required prosthesis length in malleostapedotomy seems possible if the distance between long incus process and stapes footplate is known and a design-dependent equation exists.

Two different techniques to facilitate reconstruction of the long incus process with bone cement: a feasibility study in human cadaveric temporal bones.

The purpose of this feasibility study was to evaluate two novel techniques facilitating bone cement repair of ossicular discontinuity between the incus and stapes. An isolated damage of the long incus process can be repaired using bone cement. However, bridging of a large gap between incus remnant and stapes head with bone cement is difficult, since viscous cement is not stable and the wet cement bridge may collapse. Ten fresh-frozen cadaveric human temporal bones were used. The long process of the incus was subtotally resected. A novel instrument and polylactide acid (PLA) scaffolds were applied to support ossicular reconstruction with bone cement. Stability of cement bridging was tested by checking for a round window reflex or motion of the stapes by palpating the malleus handle. Both the instrument as well as the PLA scaffolds were relatively easy to insert into the middle ear. However, bone cement adhered to the instrument irrespective of cement viscosity and contact time of the instrument with the ossicles. The bone cement plug had to be detached and sculptured. By contrast, PLA scaffolds could be used in a standardized manner and generated stable cement reconstructions. Curved PLA scaffolds were superior to straight ones. Initial results in cadaveric human temporal bones suggest that implantable PLA scaffolds might be suitable to support bone cement repair, even in very large defects of the long incus process.