Ossicular geometry and the choice of technique for ossiculoplasty

The dimensions of the space between the handle of the malleus and the plane of the head of the stapes have been investigated in 31 preserved temporal bones and 20 patients with defects of the incus. The width (A) and depth (B) were measured directly and other dimensions were then calculated. In the preserved temporal bones A varied between 0.5 and 3 mm (mean 2.0 mm), while for the patients the range was 1.5-3.8 mm (mean 2.2 mm). The dimension B varied between 1 and 2.5 mm (mean 1.7 mm) in the temporal bones and between 0 and 2 mm in the patients (mean 0.9 mm). This difference is statistically significant (P less than 0.0001). The angle at which a graft placed directly between the stapes head and malleus handle would lie relative to the long axis of the stapes varied between 14 degrees and 71 degrees in the temporal bones (mean 49 degrees) and between 0 degrees and 79 degrees in the patients (mean 63 degrees). This difference is also statistically significant (P less than 0.001). These differences may be due to chronic Eustachian tube dysfunction or to a tendency of the malleus to become displaced medially when it is not supported by the incus/stapes complex. These findings have significant implications for the mechanical properties of different methods of ossiculoplasty, and the relative position of the malleus and stapes should be taken into account when choosing the technique to be used in an individual case.