How do cartilage and other material overlay over a prosthesis affect its vibration transmission properties in ossiculoplasty?

Objective The prosthesis/eardrum interface is often deliberately modified by cartilage overlay, or by soft tissue in-growth. We examined the effects of vibration transmission to the footplate of inserting cartilage of varying sizes, and materials of varying rigidities. Study design and setting Using fresh human cadaveric temporal bones, stapes vibrations were measured. A partial ossicular reconstruction prosthesis was covered with differing materials and cartilage sizes. Materials used included glass (rigid), cartilage (intermediate), and Merocel® (soft). Cartilage sizes varied in size relative to the prosthesis head. Results Rigidity of material had little impact. Cartilage size had an impact, with smaller cartilage covers performing best. Conclusion Larger cartilage sizes performed worse. This could be a result of increased tension on the eardrum from larger cartilage size. There is little impact stiffness of interposed material stiffness. Significance Cartilage of the size used clinically has little impact on vibration transmission to the footplate. A wide range of materials could clinically be interposed over the prosthesis.