The malleus-stapes offset.
BACKGROUND
The malleus-stapes offset create challenges during ossiculoplasty, specifically the positioning of an interposed incus or replacement prosthesis relative to the manubrium.


OBJECTIVE
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.


METHODS
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.


CONCLUSIONS
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.
Todd
N Wendell
NW
Department of Otolaryngology, Emory University, 1365A Clifton Road, Atlanta, GA 30322, U.S.A. ntodd@emory.edu
D000328:Adult; D001837:Body Weights and Measures; D002102:Cadaver; D004424:Ear Canal / Q000033:anatomy & histology; D006801:Humans; D008307:Malleus / Q000033:anatomy & histology*; D008416:Mastoid / Q000033:anatomy & histology; D013199:Stapes / Q000033:anatomy & histology*; D013701:Temporal Bone / Q000033:anatomy & histology