Zur Gefahr einer Fraktur der Fußplatte durch unterschiedlich große TORP-Prothesenfüße

Background: A columella-prosthesis is the typical reconstruction procedure of the ossicular chain in cases with a destroyed stapedial arch. Lightweight titanium prostheses are commonly used for this type of surgery. The smaller the prosthesis foot the lower the risk of dislocation and friction of the prosthesis with the bony rim of the oval niche. However, using a smaller prosthesis foot, fracture of the footplate and penetration of the prosthesis into the inner ear are conceivable. Methods: Using fresh temporal bone preparations, lacking the stapedial arch, in conjunction with a load cell, the force needed to fracture the footplate was measured. Different prostheses with different foot diameters (0.2-0.8 mm) were used in these experiments. Furthermore, a human stapes was evaluated morphologically by scanning electron microscopy. Results: The forces leading to fracture of the footplate were measured to be between 250 mN and 980 mN. Statistical analysis showed no significant difference between 0.2 mm and 0.8 mm prosthesis foots. Moreover, different forces were attributed to varying thickness of the stapes footplate. In scanning electron microscopy the rough and uneven bony surface of the footplate could be demonstrated. Conclusion: Due to the uneven footplate, only punctual contact of the prosthesis foot can be achieved. Hence, the risk of footplate fracture is not considerably higher by using smaller diameters. However, the use of smaller feet in upcoming generations of TORPs seems to be appropriate.