ABSTRACT
A biomechanical study of the otosclerosis with a middle ear model, using the Finite Element Method was made. The first step of this work was the construction of the tympano-ossicular chain of the middle ear (eardrum and the three ossicles, malleus, incus and stapes) including ligaments (superior, lateral and anterior of the malleus, superior and posterior of the incus, annular ligament of the stapes) and two muscles (tensor tympani and stapedius), based on computerized tomography
1 INTRODUCTION
Otosclerosis is a disease of the ear characterized by a fixation of the stapes (one of the three ossicles of the middle ear) and causing hearing loss. It is a disease that affects twice as many women as men and is genetic in nature. When the vibration of the stapes doesn’t render correctly due to overgrowth of bone in this area (otosclerosis), conductive hearing loss is experienced. Sometimes, otosclerosis spreads to the inner ear and then a sensorineural hearing impairment may result due to interference with the nerve function. The inheritance is thought to be autosomal dominant with perhaps variable penetrance. A recent study found the rate of otosclerosis to be significantly lower in patients who received the measels vaccination (Arnold et al., 2007). Histologically, otosclerosis appears in two phases: the active or spongiotic phase (otospongiosis) and the mature or sclerotic phase. The active phase is characterized by multiple groups of active cells, including osteocytes, osteoblasts and histiocytes, with a spongy appearance due to vascular dilation secondary to bone reabsorption of the osteocyte surrounding the blood vessels (Velegrakis, 2011). More efficient treatment for this disease is surgical. The stapes is totally or partially replaced by a prosthesis (stapedectomy or stapedotomy respectively) allowing the passage of sound to the inner ear. Over time, various materials, such as stainless steel,
images (Gentil et al., 2014). The geometry was obtained from slices with 0.5 mm thickness. The finite element software ABAQUS was used to handle the numerical simulations (Hibbit et al., 2004). For the ossicles, tetrahedral elements with four nodes were used (Abaqus C3D4 element), assuming an isotropic behaviour, and with elastic properties obtained from the literature (Prendergast et al. 1999). The ligaments and muscles were modelled using linear elements of type T3D2. For the ligaments, the present study used a hyperelastic nonlinear behaviour, based on the Yeoh constitutive model (Yeoh, 1990; Martins et al., 2006; Gentil et al., 2011). The connection between the malleus and the incus, simulating the incudomalleolar joint, is done using contact formulation. The basic Coulomb friction model available in the ABAQUS software is used (Hibbit et al., 2004), being the friction rate set to 0.7 (Gentil et al. 2007).
