Orientation of the Manubrium Mallei: Inexplicably Widely Variable

Background: There is no consensus why the manubrium of the malleus, as viewed clinically through the external ear canal, generally points downward and posteriorly. Objectives: To depict the alignment of the handle of the malleus, viewed clinically through the external auditory canal, relative to the zygomatic arch, the Frankfort plane, and a visual plane proxy and relative to the horizontal semicircular canal. Also, to assess bilateral symmetry and manubrium alignment relative to mastoid pneumatization. Study Design: Postmortem anatomic dissection of 41 bequeathed adult crania without clinical otitis. Methods: The line of the manubrium as viewed through the external ear canal was measured relative to the Frankfort plane, to a proxy of the visual plane, and to the zygomatic arch. Mastoid sizes were determined radiographically. In a subset of 10 crania additionally studied by computed tomography, the manubrium position was checked relative to the horizontal semicircular canal. Results: Relative to the zygomatic arch and Frankfort and visual planes, the range of manubrium angles was at least 45 degrees. Bilateral symmetry was found, each r 0.38 or greater ( P < .05). Relative to the horizontal canals, the range of manubrial angles was 30 degrees, with symmetry suggested. Alignment did not correlate with mastoid pneumatization. Conclusion: Manubrium orientation as viewed through the external auditory canal is not obviously explicable. The wide variety of manubrium orientations may explain the manubrium‐stapes offset that perplexes manubrium‐stapes surgical constructions.