Tympanic Membrane Boundary Deformations Derived from Static Displacements Observed with Computerized Tomography in Human and Gerbil

Abstract

The middle ear is too complex a system for its function to be fully understood with simple descriptive models. Realistic mathematical models must be used in which structural elements are represented by geometrically correct three-dimensional (3D) models with correct physical parameters and boundary conditions. In the past, the choice of boundary conditions could not be based on experimental evidence as no clear-cut data were available. We have, therefore, studied the deformation of the tympanic membrane (TM) at its boundaries using X-ray microscopic computed tomography in human and gerbil while static pressure was applied to the ear canal. The 3D models of the TM and its bony attachments were carefully made and used to measure the deformation of the TM with focus on the periphery and the manubrium attachment. For the pars flaccida of the gerbil, the boundary condition can, for the most part, be described as simply supported. For the human pars flaccida, the situation is more complicated: superiorly, the membrane contacts the underlying bone more and more when pushed further inward, and it gradually detaches from the wall when sucked outward. In gerbil, the attachment of the TM to the manubrium can be described as simply supported. In human, the manubrium is attached underneath the TM via the plica mallearis and the contact of the TM with the bone is indirect. For both human and gerbil, a simple boundary condition for the peripheral edge of the pars tensa is not appropriate due to the intricate structure at the edge: the TM thickens rapidly before continuing into the annulus fibrosis which finally makes contact with the bone.

Validation Method of a Middle Ear Mechanical Model to Develop a Surgical Simulator

“…The ratio of displacements at positive/negative pressures was computed at approximately 1.8 which is in good agreement with experimental observations in human temporal bones with a ratio ranging between 1.8 and 1.9 [Hüttenbrink, 1988;Dirckx and Decraemer, 1991;Gea et al, 2010]. The mean ratio remained unchanged after the suppression of cochlea, stapes and stapedial tendon, while rigidifying the annular ligament influenced the umbo displacement below -200 daPa.…”

“…This observation suggests that the cochlea participates in the transfer function for high frequencies between 2,000 and 8,000 Hz. Figure 6 compares our model to previously published data in temporal bone specimens [Hüttenbrink, 1988;Dirckx and Decraemer, 1991;Gea et al, 2010] and to another FEM calculation [Wang et al, 2007]. The measured umbo displacement in our model was in good agreement with the experimental data.…”

“…Experimental measurements on 6 temporal bones using a laser Doppler vibrometer [Gan et al, 2004b] and results from our approach are represented. Results from our approach are compared to experimental observations on temporal bones [Hüttenbrink, 1988;Dirckx and Decraemer, 1991], two temporal bone results reported by Gea et al [2010] and one other FEM [Wang et al, 2007]. dropped to 0.124 mm and 0.324 mm at -400 and +400 daPa, respectively, yielding a mean displacement ratio of 2.13 (range: 1.72-2.62), which was higher than the one in nominal condition, indicating that the rigid footplate reduced the lateral displacement more than the medial movement. Again for moderate pressures (between -200 and +200 daPa), displacements were not different from the nominal condition.…”

Elastic characterization of the gerbil pars flaccida from in situ inflation experiments

“…Gea et al (2010) found in their work on boundary deformations of the tympanic membrane a simply supported boundary condition for the pars flaccida at the bony edge. However, at the crease between the pars flaccida and the pars tensa, they found that the boundary was not perfectly fixed.…”

On the connection between the tympanic membrane and the malleus

“…In the literature, the TMC has been assigned different names, including manubrial fold Ferrazzini, 2003), stria 50 mallearis (Hoffstetter et al, 2010), plica mallearis (Gea and Decraemer, 2010;Gulya and Schuknecht, 1995) or simply TM-malleus attachment (Koike et al, 2002). Multiple studies have attempted to investigate the functional role of the TMC through finite element modeling, yet their conclusions are not aligned.…”