Hypothesis: To delineate quantitatively the spatial relationships of the utricle, saccule, and stapedial footplate, to locate the hole on the footplate, and to analyze the insertion depth into the vestibule and the direction of the piston during stapedotomy.
Background: The quantitative three-dimensional (3D) configuration of the utricle, saccule, and stapedial footplate is undetermined, and the stapedotomy procedures should be improved.
Methods: Four temporal bones were extracted from the fresh cadavers and were undecalcified polymer-embedded. The specimens were sectioned into serial 50-mum-thickness slices. After image processing and 3D reconstruction, a cartesian coordinate system was established to display the spatial relationships of the utricle, saccule, and stapedial footplate in the 3D Studio Max scene. The configuration of the utricle, the saccule, and the "vestibular cleft" was delineated quantitatively with the contour map method. With this contour map, any distance between one point at the surface of the footplate and another point at the surface of the utricle or saccule and its orientation can be measured.
Results: There was a V-shaped cleft between the utricle and the saccule named vestibular cleft. The angle of the cleft was 50.30 degrees +/- 19.90 degrees . The apex of the cleft always directed anterosuperiorly, whereas beneath the posteroinferior part of the footplate was an open and deep "seabed." The vertical distances between points on the tympanic surface of the footplate and points on the surface of the utricle or saccule were measured. The vertical distance from the center point of footplate to the vestibular end organs was 2.20 +/- 0.548 mm, the maximum distance being 3.0 mm, whereas the minimum distance was 1.6 mm.
Conclusion: The posteroinferior area near the central point of the footplate is the optimal position for the fenestra through which the piston can be inserted relatively safely into a depth of 0.8 to 1.0 mm in the vestibule. If the deep end of the piston is inclined inferiorly and posteriorly by 8 to 10 degrees, respectively, the piston will be farther from the vestibular end organs. These manipulations may enhance surgical safety and efficiency in stapedotomy.