Background: The malleus-stapes offset create challenges during ossiculoplasty, specifically the positioning of an interposed incus or replacement prosthesis relative to the manubrium.
Objectives: To depict the malleus-stapes offset, its relationship to the orientation of the manubrium as viewed through the external ear canal relative to a horizontal plane, and mastoid pneumatization size.
Study Design: Postmortem anatomic dissection of 41 bequeathed adult crania (82 temporal bones) without clinical otitis.
Methods: The malleus-stapes offset was analyzed both as a surgeon does intraoperatively and from above through the tegmen tympani. Mastoid sizes were determined radiographically.
Results: From the surgeon's perspective, for the right ear, the “height” (manubrium to caput stapedis) ranged from 0 to 1.5 (mean, 0.5) mm; the “horizontal” offset ranged from 1.0 to 4.0 (mean, 2.2) mm. Differences in angular offset, as viewed transcanally versus trans-tegmenally, averaged 8.5 degrees (range to 53 degrees). Both height and horizontal offset exhibited wide intersubject variability, quite weak bilateral symmetry, and no relationship with either manubrium orientation or mastoid size.
Conclusion: Reliable determination of the malleus-stapes offset is difficult. Because the error of visual offset assessment exceeds the generally accepted 45 degrees alignment allowance for an ossicular prosthesis, visualized ossiculoplasty alignment should be perfect. The ranges of manubrium-stapes offset do not correlate with either manubrium orientation or the extent of mastoid pneumatization.