Learning Objectives: • A new concept of a self-adapting middle ear implant for ossicular chain reconstruction in Tympanoplasty • The prosthesis has a spring-damper-element, that conducts the sound and adapts the length of the prosthesis • The spring-damper-element is made of implantable silicone material.
Introduction: The Tympanoplastic-III is a common method to treat conductive hearing loss by reconstructing the ossicular chain with a passive prosthesis. However, the state-of-art prostheses can only be adjusted intraoperatively and cannot adapt to the postoperative changes. Hence, suboptimal tensions on the tissues and hearing may result. Furthermore, these changes may cause prosthesis luxation, if the prosthesis is too short, or extrusion, if it is too long. Both complications require revision surgery.
Methods: We propose a new postoperative adjustable prosthesis for ossicular chain reconstruction with a spring-damper-element (SDE). The SDE conducts the sound waves from the prosthesis head to the prosthesis foot, while it can adapt the distance between them. The SDE consists of a closed elastic cover (spring) and a fluid fill (damper), both made of implantable silicone material. Under dynamic loads (e.g. sound waves) the damper stiffens and conducts. Under static loads (e.g. ambient pressure variations), the damper yields to a constant force when the spring contracts or extends the prosthesis.
Results: We have built a prototype as total ossicular replacement prosthesis (TORP). We have tested our prototype in our custom middle ear model. The prototype was built too long for the model, so that we could simulate a suboptimal reconstruction. Our preliminary measurements on the stapes footplate response to sound showed that the sound conduction of our prototype was approx. 4.5 dB higher compared to a commercial TORP of the same length. In a second experiment, we could show that the prototype could reduce the tension on the stapes footplate under varying ambient pressure compared to the commercial TORP.
Conclusion: Our results show, that an implantable SDE can be manufactured and it is a promising way to limit the preload, to prevent extrusion, stabilize the prosthesis against luxation and maximize sound conduction, so that the complications can be reduced to a minimum.
