Is the Prosthesis Length in Malleostapedotomy for Otosclerosis Revision Surgery Predictable?

Abstract

The clinical practice will show whether a preoperative calculation of expected prosthesis length in MS based on the length of the formerly used stapes prosthesis is possible and helpful.

Parameters for novel incus replacement prostheses

“…A prerequisite for the development of prototypes is the access to dimensions and distances which are necessary to conceptualize shape and size. 3D reconstructions generated on micro-CT data of the ossicular chain allow the creation of sectional images and, consequently, measurement of dimensions and virtual distances at points that are not accessible in temporal bone specimens with conventional measuring instruments [12]. They have proven to be a reliable source for designing middle ear prostheses [13].…”

Design-Dependent Calculation of the Prosthesis Length in Malleostapedotomy

“…Functional length (distance from wire onset to barrel end) of MS prostheses was calculated as described previously. 5 The mean offset width (anterior-posterior distance between malleus handle and center of the footplate) as well as factors and addends determined in that study were applied for both mathematical operations. The specimen-related results differed only minimally in the present study.…”

“…According to previously published measurements, 5 the horizontal part of prostheses must be approximately 2.2 mm long to bridge the offset width between malleus and footplate. The length of the vertical part was calculated by adding 0.8 mm to the distance between long incus process and footplate; 0.5 mm was added for insertion of prosthesis into the vestibule.…”

“…According to previously published measurements, 5 2.5 mm was added to the distance between the long process of the incus and the footplate. After trimming of prosthesis to the calculated length, the wire was bent just beneath the loop along a solid quadrant with a 2 mm radius.…”

“…A recently published study based on micro-CT data showed that the required prosthesis length in MS could be estimated if the distance between long incus process and footplate or the length of the formerly used stapes prosthesis is known. 5 Equations were constructed to estimate the required length of bent and rectangular prostheses. The purpose of this study is to test the reliability of those equations in human temporal bone specimens.…”