A micro-computed tomographic study: determination of the angle between the tympanic membrane and stapes footplate in a total ossicular reconstruction prosthesis reconstruction.

OBJECTIVES: To examine the anatomical relationship of the angles between tympanic membrane and stapes footplate and the variation of these angles among different temporal bones in order to characterize the optimal shape of total ossicular reconstruction prostheses (TORPs). METHODS: Ten specimens of human temporal bones were prepared for examination with micro-computed tomography. Five of the 10 temporal bones were implanted with 3 types of TORPs before subjecting them to micro-computed tomography. The angles between tympanic membrane and stapes footplate were determined. The contact of the TORPs to these structures was assessed. RESULTS: The angle between the stapes footplate and the tympanic membrane was, on average, 25.9 degrees in a plane along the transverse axis of the stapes footplate and 24.6 degrees in a plane along the longitudinal axis of the stapes footplate. Consideration of these angles in TORPs resulted in an optimal contact with the tympanic membrane and stapes footplate, especially for prostheses with a large foot. CONCLUSION: TORPs should be adjusted in shape before insertion into the middle ear. Further developments should consider prostheses with preadjusted angles or appliances for the exact modification of the prostheses during surgery.

Morphology of the malleus handle and the comparison of different prostheses for malleostapedotomy.

OBJECTIVES: To assess malleus morphology to characterize optimal sites for prosthesis attachment in malleostapedotomy and to examine attachment, position, and depth of penetration in the vestibule of the 3 most used prostheses. METHODS: Ten mallei were processed for histologic examination with the light microscope. Using digitized video images of the histologic slices, the diameters, circumference, and shape of the specimen were determined. Implantation of 3 prostheses (Gyrus Nitinol piston, Storz titanium stapes piston, and Kurz malleovestibulopexy piston), was performed in 3 temporal bones for a total of 27 implantations. RESULTS: The cross-section of the malleus just distal to the lateral process shows an inclined oval shape with a mean minimum diameter of 0.84 +/- 0.10 mm, a mean maximum diameter of 1.02 +/- 0.23 mm, and a mean circumference of 3.23 +/- 0.49 mm. The quality of attachment to the malleus, the position of the prosthesis piston, and the depth of penetration were reliable for the Storz titanium stapes piston, satisfactory though variable for the Gyrus Nitinol piston and poor for the Kurz malleovestibulopexy piston as judged by contact with the malleus surface and predictability of insertion depth into the vestibule. CONCLUSION: The oval and inferoanteriorly inclined shape of the malleus distal to the lateral process requires the use of a prosthesis capable of molding itself to its surface for reliable attachment. To achieve the correct perpendicular position of the piston as it relates to the stapedotomy opening, individualized adaptation of the prosthesis shaft and loop to the anterior position of the malleus should be made in situ.