Experimental study of the acoustic properties of incus replacement prostheses in a human temporal bone model

Many middle ear prostheses are available for reconstruction of a missing or damaged incus. Little is known of the relative acoustic performance of these prostheses in vitro and the parameters (mass, shape, tension, angulation, area of head) that modify this performance. This report describes experiments in a human temporal bone model comparing the effect on stapes displacement of six commercially available incus replacement prostheses (IRP). Measurements were performed using a laser Doppler vibrometer before and after incus removal and IRP placement between the tympanic membrane (TM) and stapes head. In addition, experiments were performed on the effect of increasing prosthesis mass, varying the tension between TM and stapes head, changing the surface area in contact with the TM, and comparing different TM contact sites. All prostheses tested showed reasonable acoustic performance compared to the baseline condition. Optimum tension between the TM and stapes head produced the best overall sound transmission. The mid-malleus and umbo locations were the best malleus contact sites; however, the posterior TM contact site also worked well. Increased mass improved low frequency transmission and impaired higher frequency transmission, whereas a larger contact area with the TM contributed to increased gain in the mid frequencies.