In this experimental animal study, a cartilage disk was interposed between a synthetic middle ear prosthesis and the tympanic membrane in guinea pigs to investigate its effect on the extrusion process of the implant. Two groups of guinea pigs were studied. One group consisted of animals in which the prosthesis was directly in contact with the tympanic membrane, and the other group consisted of animals in which a cartilage disk had been inserted between the head of the prosthesis and the tympanic membrane. Before histologic processing, in situ inspection was performed with an operating microscope. After fixation and embedding, light microscopic and transmission electron microscopic examination were performed. We studied the histopathologic aspects of the tympanic membrane with regard to the protrusion and extrusion processes of the middle ear implant. In this experimental model, protrusion and extrusion of a hydroxylapatite middle ear prosthesis was greatly reduced by interposition of a cartilage disk. Further clinical evaluation of these experimental results is needed in the human middle ear.