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Inicio Acta Otorrinolaringológica Española Design and Experimental Analysis of a New Malleovestibulopexy Prosthesis Using a...
Journal Information
Vol. 66. Issue 1.
Pages 16-27 (January - February 2015)
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2391
Vol. 66. Issue 1.
Pages 16-27 (January - February 2015)
Original article
DOI: 10.1016/j.otoeng.2014.02.023
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Design and Experimental Analysis of a New Malleovestibulopexy Prosthesis Using a Finite Element Model of the Human Middle Ear
Nueva prótesis de maleovestibulopexia. Diseño y análisis experimental en un modelo computarizado 3D basado en elementos finitos
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Luis A. Vallejo Valdezatea,b,c,
Corresponding author
, Antonio Hidalgo Otamendid,e, Alberto Hernándezd,e, Fernando Lobod, Elisa Gil-Carcedo Sañudoa,b, Luis M. Gil-Carcedo Garcíaa,b,c
a Cátedra de Cirugía, Oftalmología, Otorrinolaringología y Fisioterapia, Universidad de Valladolid, Valladolid, Spain
b Servicio de Otorrinolaringología, Hospital Universitario del Río Hortega, Valladolid, Spain
c Instituto de Neurociencias de Castilla y León (INCyL), Valladolid, Spain
d Centro para la Investigación y el Desarrollo en Automoción (CIDAUT), Valladolid, Spain
e Centro para el Estudio y Control del Ruido (CECOR), Valladolid, Spain
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Figures (12)
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Tables (3)
Table 1. Characteristics and Mechanical Properties Used for Designing the Different Elements That Make up the Model of the Ear Using the Finite Elements Method.
Table 2. Physical Characteristics of Various Materials Considered for Prosthesis Manufacture.
Table 3. Mechanical Properties of Titanium.
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Abstract
Introduction and objective

Many designs of prostheses are available for middle ear surgery. In this study, we propose a design for a new prosthesis, which optimises mechanical performance in the human middle ear and improves some deficiencies in the prostheses currently available.

Our objective was to design and assess the theoretical acoustic–mechanical behaviour of this new total ossicular replacement prosthesis.

Methods

The design of this new prosthesis was based on an animal model (an iguana). For the modelling and mechanical analysis of the new prosthesis, we used a dynamic 3D computer model of the human middle ear, based on the finite elements method (FEM).

Results

The new malleovestibulopexy prosthesis design demonstrates an acoustical–mechanical performance similar to that of the healthy human middle ear. This new design also has additional advantages, such as ease of implantation and stability in the middle ear.

Conclusions

This study shows that computer simulation can be used to design and optimise the vibroacoustic characteristics of middle ear implants and demonstrates the effectiveness of a new malleovestibulopexy prosthesis in reconstructing the ossicular chain.

Keywords:
Middle ear mechanics
Finite elements method
Middle ear prosthesis
Ossiculoplasty
Malleovestibulopexy
Total ossicular replacement prosthesis
Resumen
Introducción

Existen numerosas prótesis diseñadas con el fin de sustituir elementos osiculares en el oído medio. En este trabajo presentamos el diseño de una nueva prótesis de sustitución osicular total anclada en el mango del martillo y analizamos su comportamiento mecanoacústico teórico.

Métodos

Para el diseño de la prótesis hemos utilizado el método de los elementos finitos (FEM) basándonos en un modelo computarizado 3D dinámico del oído medio humano, analizando su comportamiento mecánico.

Resultados

La prótesis resultante presenta un comportamiento mecanoacústico teórico superponible al del oído humano sano. Posee, además, otras ventajas biológicas como son estabilidad y la facilidad de implantación.

Conclusiones

La simulación computarizada puede ser utilizada para diseñar y optimizar las características vibroacústicas de prótesis implantables en el oído medio. Mostramos la eficiencia mecanoacústica de un nuevo diseño de prótesis de maleovestibulopexia útil en la reconstrucción de la cadena osicular.

Palabras clave:
Mecánica del oído medio
Método de los elementos finitos
Prótesis de oído medio
Osiculoplastia
Maleovestibulopexia
Prótesis de sustitución osicular total
Full Text
Introduction

Repairing the small bones of the middle ear in processes in which its integrity could be compromised (tumoral, infectious, traumatic, etc.) has given rise to numerous prosthesis designs aimed at mitigating this damage. These designs vary in both their morphology and in the material used in fabricating them, with different mechanic and biological behaviours. However, due to the variability of factors that affect ossicular reconstruction, it is not always possible to determine and compare in vivo the consequences of the mechanical and acoustic modifications induced in the reconstructed ear.

Conventional total ossicular replacement prostheses (TORP) currently sold (located below the tympanic membrane) present various deficiencies, such as the lack of stability after placement in the middle ear, the possibility of contact with the osseous frame (notably reducing its mechanical and acoustic efficiency) and its possible extrusion from tympanic damage. In the case of the TORPs anchored in the manubrium of the malleus, or hammer handle (malleovestibulopexy prosthesis), breakage of the hammer handle has been seen from its possible vascular privation.

We now have information technology and mathematical means based on the finite elements method (FEM) available that we can use to analyse the behaviour of both the healthy ear and the ear repaired surgically. This obviates the factors that induce variability in the results (intratympanic pressure, scaring, pneumatisation, etc.). These three-dimensional (3D) models also allow us to optimise not only the design, but the mechanical and acoustic behaviour of any ossicular replacement prosthesis without needing to turn to biological models. Our group has been analysing and designing ossicular replacement prostheses using a FEM-based 3D computer model years.1,2

With this study we present a new total ossicular replacement prosthesis that functionally links the hammer handle, to which it is anchored, with the inner ear (malleovestibulopexy [MVP]) and that attempts to resolve some of the disadvantages of the prostheses currently sold. The FEM with which it has been designed and validated has allowed us to optimise its physical characteristics (morphology, mass, and rigidity) and define the optimal contact position in the middle ear, not only for transmitting sound efficiently, but also for reducing the possibility of extrusion or mobilisation after its implantation. Its biological and mechanical-acoustic characteristics make it an ossicular replacement prosthesis to keep in mind in reconstructive surgery on the middle ear.

Methods3D Computerised Model Based on Finite Elements

The FEM is a numerical tool oriented towards its implementation in computers used in engineering to predict, in the design stage, how the real product would behave in the face of external alterations produced by practically any physical phenomenon. The final goal in using these methods is avoiding, as much as possible, resorting to the costly–in time and money–process of constructing prototypes and submitting them to (sometimes destructive) trials to test whether they behave in accordance with their specifications under working conditions.

This method does not consider the structure as a continuum (as occurs with the classic calculation methods); it considers each solid as a set of small elements of finite dimension related among themselves through contact nodes or links. The behaviour of each of these elements is obtained by formulating a system of differential and algebraic equations. The unknowns are the node displacements, based on which we will express the displacements of the inner points of each element formulating a hypothesis. By assembling the systems of equations, a system for every solid with an elevated number of equations is obtained, which can be solved using a computer.

Fundamentally, what is involved is solving the movement equation:

where [M]=mass matrix, [C]=buffer matrix, [K]=rigidity matrix, {u}=vector of displacements, {f(t)}=vector of forces.

The hypotheses to be considered in the development of the FEM are the following:

  • -

    The continuous medium is divided into a finite number of elements, whose behaviour is defined through a finite set of parameters or degrees of freedom.

  • -

    The elements are connected to each other through a discrete number of points, called nodes, basically located in the contours (although there can be interior nodes). The node displacements are the unknown variables of the problem.

  • -

    The field of displacements within each element is determined by the form functions, which relate them with the node displacements of that element. That is, the element is deformed, but the deformation is known as a function of the displacements of its nodes.

  • -

    The form functions are chosen by the user, when the model is created, by selecting the type of element. They define, uniquely, the field of displacements within each finite element, based on the nodal displacements of each element.

  • -

    A system of forces concentrated on the nodes is determined, in such a way that the tensions in the contour are balanced with any of the charges distributed.

The steps to be carried out in the FEM are the following (Chart 1):

  • 1.

    Mesh the structure in finite elements. This step will characterise the degree of confidence in the results obtained afterwards.

  • 2.

    Formulate the behaviour equation and determine the properties of each element based on the geometry of the problem, the properties of the material, the nature of the problem and the data of charges. The type of finite element most appropriate for solving the problem will be chosen.

  • 3.

    Assemble the equations for each element. Application of the forces and exterior moments.

  • 4.

    Introduce the conditions of contour in the assembled matrix.

  • 5.

    Solve the system of equations and obtain the answer in tensions or displacements.

(0.12MB).

The model of the simulated ossicles of the human ear was obtained using Hypermesh 7.0 software (the characteristics by which we defined each of these elements are shown in Table 1). The mesh was exported to MSC Patran software for pre-processing and then later processed in MSC Nastran software. Once the model was processed, we carried out new adjustments in MSC Patran.

Table 1.

Characteristics and Mechanical Properties Used for Designing the Different Elements That Make up the Model of the Ear Using the Finite Elements Method.

Element number  Name  Density (kg/m3Young's modulus (Pa)  Poisson coefficient  Absorption rate 
Biological tissue (membrane)  1200  3. 30E+07  0.29  0.35 
Stapes muscle  1200  5.20E+05  0.2  0.2 
Tympanic tensor muscle  1200  2.60E+06  0.2  0.2 
Tympanic ring  500  2.10E+15  0.29  0.35 
Incus ligaments  1200  6.50E+05  0.29  0.3 
Upper ligament of the malleus  1200  6.50E+05  0.3  0.25 
Lateral ligament of the malleus  1200  2.10E+07  0.3  0.25 
Malleus (neck)  4530  1.41E+10  0.2  0.05 
10  Malleus (manubrium)  3700  1.41E+10  0.2  0.05 
11  Malleus (head)  2550  1.41E+10  0.2  0.05 
12  Fibrous tympani-malleus union  50  2.00E+10  0.29  0.25 
13  Incus-malleus articulation  1200  2.00E+10  0.4  0.25 
14  Incus-stapes articulation  1200  7.00E+05  0.3  0.3 
15  Short apophysis of the incus  2260  1.41E+10  0.2  0.05 
16  Body of the incus  2360  1.41E+10  0.2  0.05 
17  Large apophysis of the incus  5090  1.41E+10  0.2  0.05 
18  Stapes  2200  1.41E+10  0.2  0.717 
37  Tympanic membrane (radial fibres)  1200  1.00E+07  0.3  0.35 
38  Tympanic membrane (parabolic fibres)  1200  1.00E+07  0.3  0.35 
52  Tympanic membrane (semi-lunar fibres)  1200  1.00E+07  0.3  0.35 

The simulated model was validated using the mean of the amplitude of displacement of the umbo. To do so, we took, as a reference, the experimental measurements of the umbo displacement carried out by Vlaming and Feenstra3 and the experimental results using a single-point laser vibrometer in 4 healthy volunteers (Fig. 1) at an intensity of 80dB. Once the experimental curve of displacement was known, the simulated model could be validated by calculating a frequency response function (FRF) that made it possible to known the umbo displacement in the simulated model and compare it with the measurement obtained experimentally.

Figure 1.

Validation of the computerised model of the ear: theoretical response in the model submitted to a stimulus of 80dB SPL comparing it to the real measurements obtained by Vlaming and Feenstra in 4 healthy individuals.

(0.39MB).

To introduce the prosthesis in the simulated model of the coupled ear, we eliminated all the elements that were going to be replaced by the prosthesis. These eliminated elements were the incus and its ligaments, the stapedial muscle and the stapes, as well as the platen.

To assess the theoretical behaviour of the new prosthesis, we analysed the displacement, impedance and transfer function (TF) in the computerised model of the ear before it was manipulated and after the prosthesis was implanted in it. The TF is the gain or difference of sound pressure measured between 2 points. The points used to calculate the TF were:

  • -

    In the model of the non-manipulated ear: the umbo and a central point in the platen.

  • -

    After inserting the new design of prosthesis: the umbo and a point of the medial (vestibular) end of the prosthesis.

The prosthesis is designed in titanium, a material biocompatible with human beings. The geometry of the prosthesis is such that it presents an elastic anchor for its union with the hammer handle, given that this bone is normally lesion-free in the diseases for which using this prosthesis is considered. The other end presents a circumferential section so it can be introduced into the oval window. This link is considered a rigid set and, in our model, is represented with rigid elements that permit a rigid union between nodes.

Results

We based our prosthesis design on animal models that had only 1 element in their ossicular chain (columella), such as birds and reptiles. Aviary models are useless for our needs given that, the oval window is arranged in a central way to the tympanic membrane (which does not occur in human beings, in whom the window niche is located in an eccentric position with respect to the tympanic membrane umbo). This eccentric disposition that is characteristic of humans is found in reptiles, specifically in the iguana (Iguana iguana), on whose columella we based our design (Fig. 2).

Figure 2.

Photograph of the middle ear of the iguana, showing the anchor of the lateral end of its only ossicular element at the central area of the membrane and the curvature of the columella.

(0.23MB).

We chose titanium as the material for manufacture as much for its proven biocompatibility as for its physical properties (mass and rigidity) that give it ideal characteristics for fabricating ossicular replacement prostheses for the middle ear. The theoretical weight of a prosthesis made with this material is 0.004g for a length of 5.5mm. Other biocompatible materials for its manufacture could have gold, platinum, and steel. The mass and rigidity of these materials place a prosthesis made from them at a disadvantage compared with another made from titanium (Table 2).

Table 2.

Physical Characteristics of Various Materials Considered for Prosthesis Manufacture.

Material  Volume (mm3Density (kg/m3Density (kg/mm3Weight (kg)  Weight (g) 
Platinum  1.01029  21450  0.00002145  2.17E−05  0.02167072 
Titanium  1.01029  4507  0.000004507  4.55E−06  0.00455338 
Gold  1.01029  19300  0.0000193  1.95E−05  0.0194986 
Steel  1.01029  7800  0.0000078  7.88E−06  0.00788026 

As far as the morphological specifics of this new prosthesis are concerned, the following points stand out:

  • -

    Lateral end: Anchor adjusted to the intratympanic facet of the middle third of the hammer handle. This type of anchor prevents the tympanic membrane from stripping from the hammer handle and any possible posterior displacement of the prosthesis. Choosing an anchor located medially to the hammer handle and that could be attached to its central section made it essential to know its size; consequently, we studied 10 hammers obtained from cadavers. The mean of the diameters in the middle third of the hammer handle was 1.2mm (±0.2mm). We considered these measurements in designing the prosthesis anchor to be 0.3mm less than the mean diameter so that, due to the elastic properties of titanium, we could achieve an optimum adjustment to the hammer handle.

  • -

    Medial (vestibular) end discretely thickened, increasing the surface of contact with the inner ear. This end could contact the perilymph directly (through a calibrated platinotomy) or a biological autologous graft (ideally vein or perichondrium) could be put between it and the prosthesis.

  • -

    A gently curved stem, avoiding losses in energy efficiency that angular prostheses show.

The titanium parameters required for the modelling are shown in Table 3.

Table 3.

Mechanical Properties of Titanium.

Material  Density  Young's modulus (MPa)  Poisson coefficient 
Titanium  4.50E−09  116000  0.34 

With these initial concepts, we proceeded to design the prosthesis using CAD and to later mesh it using Hypermesh 7.0, exporting the mesh form created to MSC Patran and obtaining the final model (Fig. 3).

Figure 3.

Mesh of the new prosthesis using the FEM. The lateral end in the shape of an elastic fork is attached to the intratympanic section of the hammer handle, while the medial end is aimed at the oval window, covering the different position between the two by the arched design of the prosthesis.

(0.21MB).

To assess the mechanical and acoustic behaviour of the prosthesis (Fig. 4), we then eliminated (in the 3D computerised model) the incus and its ligaments, as well as the stapes, inserting the model of the prosthesis in its place (Fig. 5). We studied the displacements of the prosthesis, the impedance if the middle ear and the TF in the ear in the model of the ear.

Figure 4.

(A) Modelling through FEM of the outer and middle parts of the human ear assembled, before any manipulation. (B) Representation of the model of the ear after replacing the incus and stapes with the new malleovestibulopexy prosthesis.

(0.41MB).
Figure 5.

(A) Global view of the model after implanting the malleovestibulopexy prosthesis object of study. (B) Position of the prosthesis in the middle ear (oblique view). (C) Position of the prosthesis in the middle ear (cranial view).

(0.32MB).

(1) Displacements. The theoretical displacement of the umbo in the computerised model, simulating a stimulus of 80dB of pressure distributed over the entire surface of the tympanic membrane; once the prosthesis was replaced in its place, it was comparable to that of the normal middle ear (Fig. 6). Fig. 7 shows the theoretical displacement of both the medial end of the prosthesis located in a position centred in the oval window and of a central point of the platen. It can be seen that the displacements of the prosthesis resemble those of the platen; the prosthesis movements are slightly greater than those of the platen, but conserving the morphology of the curve.

Figure 6.

Theoretic displacement of the umbo in the 3D model of the ear at 80dB SPL before being manipulated and after implanting of the malleovestibulopexy prosthesis.

(0.36MB).
Figure 7.

Comparison of the theoretical displacement, in the model of the ear, of a central point of the platen of the stapes and a central point of the medial end of the malleovestibulopexy prosthesis mobilised by a stimulus of 80dB SPL of intensity.

(0.39MB).

Another parameter to bear in mind is the prosthesis displacement when the intratympanic pressure is modified. We calculated the theoretical displacement of the distal end of the prosthesis submitted to variations of physiological and supra-physiological intratympanic pressure (between +400 and −400daPa) and, due to the anchoring of the prosthesis in the hammer handle, these displacements were less than 24.96754μm, at intratympanic pressures in the range described.

Finally, we compared the displacement of the umbo of this recently designed prosthesis with another manufactured in the same material but located under the posterior superior tympanic quadrant. It can be seen that the second one shows erratic displacement, above all at high frequencies (Fig. 8).

Figure 8.

Comparison of the theoretical displacement of the umbo in the ear model at 80dB SPL in 3 different situations. In the model without manipulation. In the model after replacing incus and stapes with the new malleovestibulopexy prosthesis. In the model after replacing incus and stapes with a conventional TORP prosthesis located below the posterior superior quadrant.

(0.39MB).

(2) Impedance. The analysis of the impedance in the model, both in a central point of the platen and in the umbo, showed minimal impedance variations after implanting the new model of prosthesis, in comparison with the model of the intact ear, as can be seen in Figs. 9 and 10.

Figure 9.

Comparison of the theoretical impedance in the model of the ear, evaluated in the umbo, before and after substituting incus and stapes with the new design of malleovestibulopexy prosthesis.

(0.34MB).
Figure 10.

Comparison of the theoretical impedance in the model of the ear, evaluated in a central point of the platen, before and after substituting incus and stapes with the new design of malleovestibulopexy prosthesis.

(0.3MB).

Fig. 9 shows the theoretical impedance of the ear calculated at a central point of the most distal (vestibular) end of the prosthesis and compared with the impedance of a central point of the platen in the model of the intact ear. Fig. 10 shows the theoretical impedance analysed at a central point of the tympanic membrane (umbo) before and after implanting the new model of prosthesis. In both cases, the theoretical impedances of the middle ear repaired with the prosthesis is slightly less, due to its smaller mass in comparison with the ossicular chain.

3) Sound transfer function. The theoretical evolution of the TF based on frequency is marginally greater in the ear after implanting the MVP prosthesis than in the model of the intact ear (Fig. 11). This is due to the smaller mass of the prosthesis in comparison with the ossicular elements it replaces.

Figure 11.

Comparison of the sound transfer function in the model of the intact ear and after implementing the new malleovestibulopexy prosthesis in it.

(0.34MB).
Discussion

Many prostheses have been designed with the goal of lessening damages to the ossicle chain in the human middle ear. Although their objective is the same, they differ in the materials used in their manufacture (ceramic, plastic or metallic) or in their morphology. The design of the great majority of these prostheses is due more to the preferences of the surgeon responsible for it than to biological physiological or mechanical-acoustic criteria. However, we now have sufficiently powerful mathematical tools available for not only designing, but also for assessing the mechanical and acoustic response of any prosthesis in the human ear before being implanted, without the need to rely on biological models.

To design the MVP prosthesis, we took animals with a single element in their ossicle chain as a model, opting for a reptile (iguana) because the medial end of its columella is located eccentrically with respect to the centre of the tympanic membrane, as in human beings.4 For the design and the analysis of the mechanical and acoustic behaviour of this ossicular replacement prosthesis, we used a 3D computerised mathematical model based on finite elements, designed by our group, just as other groups had done in the past.5 These mathematical models make it possible to optimise the morphology or the acoustically ideal position of the prosthesis to place it in the middle ear, in addition to being able to analyse its mechanical response in the face of various physiological or pathological situations. We placed the medial end of the prosthesis in a central position of the platen, because this point is acoustically ideal when implanting a total ossicular replacement prosthesis (TORP).6

We chose titanium as the perfect material for manufacturing the prosthesis because of its proven biocompatibility and its physical characteristics (mass and rigidity) that provide it with optimal qualities for making prostheses for ossicular replacement in the middle ear.7

The ossicular replacement prosthesis that we present possesses a series of advantages that we can group into 2 types: mechanical-acoustic and biological.

Mechanical and Acoustic Advantages

Various studies have shown that any peripheral section of the tympanic membrane is more mobile than the central section, in contact with the hammer handle.8 However, this fact does not imply that these peripheral sections are the optimal positions under which to place a prosthesis. The movement transmitted from the tympanic membrane to the hammer handle is due to the strength from the complex movement that occurs in the various sections of the membrane based on the intensity and frequency of the stimulus that reaches it.9 Choosing to anchor this prosthesis in the hammer handle, instead of under the superior tympanic quadrant, is beneficial in that it takes advantage of the resulting end of the movement of the entire tympanic membrane and not only of the section of the tympanic membrane under which it lies.10 Goode11 indicated earlier, as an ideal characteristic of a prosthesis, that its support occupied a central position in the tympanic membrane. In animals that have a columella in their middle ear, such as birds and reptiles, the lateral section of this columella is centred in the tympanic membrane and not in a peripheral area. In this sense, this new prosthesis imitates the evolutionary solution in middle ears with a single element of transmission towards the inner ear. This advantage is not only evolutionary because, as Bance12 pointed out, prostheses anchored in the hammer handle present better transmission of the sound vibration than those located under the tympanic membrane.

Prosthesis placement in the hammer handle also favours the proper use of a hypothetical auditory action (not well studied) of the tympanic tensor muscle. In a few studies, however, it is stated that prostheses located under the posterior superior quadrant are more stable than the same prostheses placed under the hammer handle.5 This is due to the design of the prosthesis analysed with a flat support surface that only contacts the handle; however, the design of the prosthesis presented here offers greater stability, given that it is attached to the hammer handle, making its displacement difficult.

Choosing to anchor the prosthesis to the hammer handle gives rise to a problem derived from the eccentric position of the oval window with respect to the centre of the tympanic membrane: the angulation needed to join the centre of the tympanic membrane with the centre of the oval window. It has been shown in experimental studies that the mean angulation in cadavers between the hammer handle and the centre of the oval window is 49° (ranging from 14° to 71°).12 To overcome this difference in position between the hammer handle and the centre of the oval window, angular prostheses have been designed, but this reduces mechanical efficiency.13 In the design that we present, we have solved this problem through a slightly curved prosthesis design, not angular, avoiding the loss of efficiency associated with the angulations.

A key situation in the transmission of mechanical energy in the middle ear is that of the tension in its elements: if they are hyper-mobile, they can be limited in efficiency, in terms of sound transmission, as if they were under excessive tension.14 To prevent the prosthesis from being short and not supporting itself correctly on the platen of the oval window or, to the contrary, being excessively long and increasing the tension in the middle ear, we proposed 4 lengths (4.5, 5, 5.5, and 6mm) and the possibility of eliminating the platen of the stapes, which would be replaced by perichondrium or vein, allowing the medial end of the prosthesis to be introduced slightly into the vestibule.

Finally, the slightly thickened design of the medial end of the prosthesis favours better sound transmission to the cochlea in the entire range of frequencies, as can be seen by analysing the displacements, impedances, and TF investigated in the computerised model.

Biological Advantages

(A) Ease of placement. Total ossicular replacement prostheses anchored in the handle of the hammer (MVP) currently sold make it obligatory to lift the section of the tympanic membrane that is inserted in this section of bone, which sometimes can favour its breakage as it deprives it of its vascular support. Anchoring the prosthesis under the hammer handle is simpler than lifting the membrane of the hammer handle and avoids limiting its vascularity.

Placement of the distal end is also simple, given that it is supported by the graft chosen to seal the oval window once open. Optionally, in well-ventilated ears (as, for example, in a revision after stapedectomy failure from incus lysis), it would even be unnecessary to support the distal end of the prosthesis in a biological graft that covers the oval window. Due to the design of prosthesis anchoring in the hammer handle, as long as the prosthesis length is optimal, we could introduce the distal end 0.5mm in a calibrated platinotomy. The majority of these current prostheses are left “free” in the middle ear and absolutely have to be supported in a graft or in the platen itself to prevent being introduced into the vestibule. In contrast, this new design prevents the introduction of the distal end due to the firm anchoring of its proximal end in the hammer handle.

(B) Absence of prosthesis displacement. One of the causes of failure in auditory recovery after tympanoplasty in which prostheses located under the posterior superior tympanic quadrant are used is their displacement, induced by variations in intratympanic pressure. This situation provokes contact between the prosthesis and the osseous frame, loosening of the prosthesis towards the hypo-tympanic membrane or displacements from its initial optimum location.

At the root of most of the diseases that will require reconstruction with total ossicular replacement prostheses are alterations in the function of the Eustachian tube that give rise to supra-physiological variations in intratympanic pressure. In comparison with the amplitudes of the physiological sound pressures, the variations of static pressure are several times greater.15 These supra-physiological conditions in the intratympanic static pressure are kept in many reconstructed ears. For this reason, the prostheses used in ossicular reconstruction can suffer displacements caused by these pressure variations: either towards the vestibule (in the case of negative pressures) or in the opposite direction (during Valsalva manoeuvres).16 This fact can mean that there is a reduction in mechanical and acoustic performance of the prostheses used, which can appear more pronounced in the prostheses located in the posterior superior tympanic quadrant, due to the greater amplitudes of movement in this area of the membrane. In contrast, prostheses anchored in the hammer handle present less displacement caused by variations of intratympanic pressure, given that anchoring the hammer to the box (tympanic tensor muscle and ligaments) limits its displacements.

(C) Vascularisation of the hammer handle. MVP-type total ossicular replacement prostheses are anchored in the hammer handle through a loop or a clip, but in both of them the design makes lifting the tympanic membrane in the ossicle mentioned obligatory. This lifting can alter the nutrition of this section of bone as it receives its vascularisation through small branches perforating the tympanic membrane. Consequently, when we performed MVP lifting the tympanic membrane from hammer handle, we often saw lysis of the section of the ossicle in which the prosthesis was anchored. With our new design, we avoid damaging the vascular supply of the handle and, consequently, its breakage for lack of vascularity.

(D) Possibility of use in fixation of the hammer head. Given that the prosthesis is anchored in the hammer handle, attic ankylosis of the head of this ossicle is not an obstacle in its use. Sectioning the neck of the hammer above the insertion of the tendon of the tympanic tensor muscle would be enough to provide the system with the freedom of movement needed for proper sound transmission.

The theoretical mechanical and acoustic characteristics of this new prosthesis, associated with its biological advantages, would indicate its usefulness in the following situations:

  • -

    Any ossicular reconstruction with persistence of the hammer handle (chronic disease of the middle ear, traumatic damage to the middle ear, etc.).

  • -

    Stapedectomy failure from lysis of the incus.

  • -

    Tympanoplasty revision surgeries.

  • -

    Congenital or acquired ossicular attic fixation.

  • -

    Surgery of attic cholesteatoma with mesotympanic extension and erosion of the stapes supra-structure.

Conclusions

The new total ossicular replacement prosthesis designed using the FEM and analysed in this study shows mechanical and acoustic behaviour comparable to that of the healthy middle ear. Its design makes displacement or extrusion more difficult and guarantees optimal sound transmission both because of its characteristics of mass and rigidity, as of the choice of anchor located in the hammer handle.

Further studies using laser vibrometry fresh cadaver temporal bone that validate the results and the above theoretical advantages are necessary.

Funding

This research was funded by the Regional Health Management of the Health Department, Board of Castilla y León (Spain) (GRS 495/A/10).

Conflict of Interests

The authors have no conflicts of interest to declare.

The prosthesis that was the object of study has been registered in the Registry of Patents and Brands with the identifying number PCT/ES2010/000522.

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Please cite this article as: Vallejo Valdezate LA, Hidalgo Otamendi A, Hernández A, Lobo F, Gil-Carcedo Sañudo E, Gil-Carcedo García LM. Nueva prótesis de maleovestibulopexia. Diseño y análisis experimental en un modelo computarizado 3D basado en elementos finitos. Acta Otorrinolaringol Esp. 2015;66:16–27.

Copyright © 2014. Elsevier España, S.L.U. and Sociedad Española de Otorrinolaringología y Patología Cérvico-Facial
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