Preliminary Model for the Design of a Custom Middle Ear Prosthesis

Hypothesis: Custom prostheses could be used to recreate the ossicular chain and improve hearing. Background: Ossicular discontinuity or fixation occurs in 55% of cases of conductive hearing loss, with most cases involving the incus. Reconstruction has been achieved by a variety of methods; however, there has been little improvement in hearing outcomes in decades. Methods: Precise measurements of anatomic dimensions, weight, and center of gravity were taken from 19 cadaveric incudes. These measurements were combined with measurements from the medical literature and micro-computed tomography (micro-CT) of cadaveric temporal bones to generate a rasterizable incus model. As a proof of concept, incudal replacements including possible anatomic variations were then three-dimensionally (3-D) printed and inserted into a cadaveric temporal bone. Results: Our measurements of cadaveric incudes corresponded well with those from the medical literature. These measurements were combined with anatomical information from micro-CT allowing identification of critical features of the incus, which remained constant. Other model features were modified to increase stability and facilitate synthesis, including broadening and thickening of the lenticular process and the incudomalleolar articulation. 3-D printed incudal replacements based on this model readily fit into a cadaveric temporal bone and successfully bridged the gap between malleus and incus. Conclusion: We have generated a model for custom 3-D synthesis of incudal prostheses. While current 3-D printing in biocompatible materials at the size required is limited, the technology is rapidly advancing, and 3-D printing of incudal replacements with polylactic acid (PLA) is of the correct size and shape.