A scanning electron microscopic study of crimping of stapedial prostheses

A scanning electron microscopic study of crimping of stapedial prostheses

Auris Nasus Larynx 39 (2012) 461–468 Contents lists available at SciVerse ScienceDirect Auris Nasus Larynx journal homepage: www.elsevier.com/locate...

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Auris Nasus Larynx 39 (2012) 461–468

Contents lists available at SciVerse ScienceDirect

Auris Nasus Larynx journal homepage: www.elsevier.com/locate/anl

A scanning electron microscopic study of crimping of stapedial prostheses Marco Fontana a,*, Emanuele Ferri b, Lucia Lora c, Gregorio Babighian c a

UOC ORL, General Hospital of Monselice (Padua), Via G. Marconi, 19, 35043 – Monselice, Padua, Italy UOC ORL, General Hospitals of Mirano and Dolo, Venice, Italy c Department of ORL-Otosurgery, Azienda Ospedaliera-Universita`, Padua, Italy b

A R T I C L E I N F O

A B S T R A C T

Article history: Received 19 June 2011 Accepted 21 October 2011 Available online 15 November 2011

Objective: The aim of this study was to evaluate, through the Scanning Electron Microscopy, the loop closure of four types of stapedial prostheses and to compare the different systems of crimping to the long process of the incus. Materials and methods: Four types of stapedial prostheses (one platinum-teflon, two different titanium and one nitinol-teflon pistons) were inserted in 40 specially prepared temporal bones simulating the in vivo stapedotomy procedure. Two pistons were crimped by single manual manoeuvre with a McGee microforceps; the remainders were self-retained and thermal-crimped, respectively. All the specimens were evaluated through the Operative Microscopy and the Scanning Electron Microscopy. Results: Through the Operative Microscopy, all prostheses apparently achieved a correct adhesion to the long process of the incus; on the contrary the Scanning Electron Microscopy study demonstrated some limits of the manual crimping and the different coupling with the ossicular chain of each type of stapedial prosthesis. Conclusion: A complete adhesion of the prosthetic loop cannot be obtained because of the irregular profile of the incus at the site of attachment of the stapedial prosthesis. Consequently, on the basis of the morphological analysis with Scanning Electron Microscopy, in the surgical practice, the preference could be given to the stapedial prostheses that achieve greater contact such as the self-retaining and thermal crimping pistons compared to the standard sized prostheses considered. ß 2011 Elsevier Ireland Ltd. All rights reserved.

Keywords: Stapedial prosthesis Crimping Scanning Electron Microscopy Stapedotomy SMart piston prosthesis Nitinol

1. Introduction Prosthesis crimping during stapes surgery is a known critical step because it remarkably affects sound transmission while exposing the middle ear and the inner ear to mechanical trauma. The complications of stapedotomy related to malcrimping can be immediate (incus dislocation, sinking of the piston into the vestibule, fracture of the lenticular process) or delayed (erosion and necrosis of the long process of the incus – LPI, dislocation of the prosthesis and loose wire syndrome – LWS) [1]. More frequently, such complications can be the result of loose crimping, overcrimping or unskilled surgical manoeuvres. Loose crimping has been postulated to cause direct microtrauma and/or vascular deficit of the LPI; it can potentially lead to abrasion, erosion and potential resorption or necrosis of LPI with a remarkable functional and anatomical impact [2–6]. A recent review cases of stapedotomy revision reported that as many as 81– 87% of revision cases demonstrated a displaced or malfunctioning prosthesis [1]. Moreover it have been reported that a malfunction-

* Corresponding author. Tel.: +39 429 788311; fax: +39 429 788311. E-mail address: [email protected] (M. Fontana). 0385-8146/$ – see front matter ß 2011 Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.anl.2011.10.008

ing prosthesis is a direct result of a malcrimping of the prosthesis [6]. These factors have all contributed to the ongoing search for an easier way to crimp the prosthesis to the incus. Research studies have focused on all the aspects of prosthesis engineering and, particularly, on the loop portion clinging to the incus. The technological goal is to design prostheses that reduce the risk of iatrogenic damage and adequately couple on the LPI. The aim of this study was to evaluate through the Scanning Electron Microscopy (SEM) the loop closure of four types of stapedial prostheses and to compare, from a purely descriptive and morphological perspective, the different systems of crimping to the LPI. 2. Materials and methods After complete removal of the eardrum, forty fresh human temporal bones were collected and drilled out, preserving the integrity of the ‘‘ossicular chain-attic-labyrinthine capsule unit’’. This term indicate an anatomical complex that can be isolated by drilling in each temporal bone and, thereafter, used to attach a prosthesis that can be observed and examined in all three spatial planes. The samples were harvested in order to obtain pictures in

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all planes: in the posterior–anterior plane to assess the positioning of the piston, the orthogonal setting and possible deformations; in the lateral–medial plane to evaluate the exact insertion through the fenestration and the orthogonal setting; in the anterior– posterior plane to highlight the position of the two ends of the loop and its anterior portion; in the inferior–superior plane, which is the optimal projection for identifying and measuring even minimal differences of the prosthesis–incus interface. In some cases the malleus handle was cut with a micro-nipper and removed to obtain the anterior–posterior projection for viewing the incus–prosthesis complex. Four different prostheses were used (ten for each type): Richards1 Platinum-Teflon piston (Gyrus ENT LLC, Bartlett, TN, USA), K-Piston-Titanium1 (Kurz, Dusslingen, Germany), Titanium a’Wengen1 clip-piston (Kurz, Dusslingen, Germany), and SMart1 Nitinol-Teflon piston (Gyrus ENT LLC, Bartlett, TN, USA) (Fig. 1). The first and the second piston were manually crimped using a Fisch-McGee micro-forceps, the third piston, a ‘‘self retaining’’ prosthesis, was positioned using a hook, the fourth piston required ‘‘thermal’’ crimping. The weights of the prostheses were comparable: all less than 2.9 mg. The Richards piston is a band-shaped prosthesis (length 4.5 mm; calibre 0.6 mm; loop’s length 3.47 mm; loop’s diameter 1.25 mm). The piston was crimped manually by a single manoeuvre to simulate the ‘‘in vivo’’ surgical procedure to avoid any further risk of iatrogenic damage. The K-Piston-Titanium is spiral band-shaped loop prosthesis (length 4.5 mm; calibre 0.4 mm; loop’s length 3.74 mm.) crimped manually. The a`Wengen1 piston is a titanium band-shaped prosthesis (length 4.5 mm; calibre 0.6 mm) with a clip anchorage exclusive system. It is fixed by simply pushing with a bimanual manoeuvre to stabilize the incus with a 458-hook. The SMart1 Nitinol-Teflon piston is an asymmetrical nitinol wire-shaped prosthesis (length 4.5 mm; calibre 0.8 mm, loop’s length 2.66 mm), crimped by thermal diffusion using a special device: the Thermal Tip1 (Gyrus ENT LLC, Bartlett, TN, USA). Nitinol is an equiatomic alloy of nickel–titanium with shapememory and superelastic properties. The nickel internal layer is electrolytically coated with a titanium external surface. The shape memory is based on the reversible solid-state phase transformation from austenite to martensite and vice versa. It is immediately activated at a temperature of 45–60 8C. If the Thermal Tip is not available, the closure is also possible using a single shot of 10-W bipolar current applied with microforceps [7]. Two operative microscopes were used for the surgical procedure: LEICA OHS/1 with auto-focus system (Leica Microsystems

GmbH, Wetzlar, Germany) and ZEISS OPMI PRO ORL (Carl Zeiss S.p.A., Oberkochen, Germany). The removal of the stapes supra-structure and the calibrated platinotomy were performed by means of an Erbium-YAG laser (twinER Er-YAG laser1) (Carl Zeiss S.p.A., Oberkochen, Germany), at the intensity of 70 mW – BIM 2, to avoid the mobile footplate from sinking into the vestibule. Each surgical step was digital-recorded via Operative Microscopy and an image acquiring system was used (OTOCS 1.0 version MS Software s.r.l. – Castelfranco Veneto, Italy). Each sample – maximum diameter of 2 cm – was embedded in a plasticine support for proper stabilization and subsequently analyzed through Enviromental Scanning Electron Microscopy (XL30 ESEM TMP, Philips, Eindhoven, Netherlands) at magnification from 38 to 800 at the C.U.G.A.S. (Centro Universitario Grandi Apparecchiature Scientifiche – University Centre for Large Scientific Equipments, Padua University, Italy). For each prosthesis we have measured and evaluated the following parameters: distance from the umbo of LPI (as measure of level of the prosthesis anchorage to LPI, according to Kwok and Fisch) [3], the max empty space (as measure of the non-contact zones or non-adhesion areas), the orthogonality with LPI (as evaluation of correct position of the prosthesis), the kind of deformation and the loop’s ends contact (as evaluation of the prosthesis crimping). 3. Results 3.1. Operative microscopy All four types of prostheses considered (Richards piston, Kpiston, a`Wengen clip piston and SMart piston) seem to have achieved a good and correct positioning without deformations in the posterior–anterior and lateral–medial projections (Figs. 2 and 3); also in the other surgical views they seem to be well wound around the LPI. As regards the orthogonal axis, no significant differences were remarked among the pistons and the distance of the loop from the umbo (according to Fisch, 1.43  0.28 mm). 3.2. Scanning Electron Microscopy (SEM) 3.2.1. Richards piston It appears crimped with an average distance of 1.39 mm from the umbo and well positioned into the opening of the stapes footplate; its loop proves to be malformed in oval shape in nine out of ten prostheses. It appears anchored to the anterior and posterior sides of the LPI, with a variable empty space between the arch and the lateral side. The surface of the loop looks smooth and regular

Fig. 1. The four types of stapedial prostheses under investigation: (a) Nitinol-Teflon SMart piston (Gyrus ENT LLC, Bartlett, TN, USA), (b) K-Piston-Titanium1 (Kurz, Dusslingen, Germany), (c) Titanium a`Wengen1 clip-piston (Kurz, Dusslingen, Germany), and (d) Richards Platinum-Teflon piston (Gyrus ENT LLC, Bartlett, TN, USA).

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Fig. 2. Stapedotomy at the operative microscope: posterior–anterior view. Platinum-teflon piston (a), K-Piston-Titanium (b), Titanium a`Wengen1 clip-piston (c) and NitinolTeflon SMart1 piston (d) appear to be well positioned and well wound around the LPI.

Fig. 3. Stapedotomy at the operative microscope: lateral–medial view. Even in this view, platinum-teflon piston (a), K-Piston-Titanium (b), Titanium a`Wengen1 clip-piston (c) and Nitinol-Teflon SMart1 piston (d) appear to be well positioned and well wound around the LPI.

and shows the marks of the microforceps. Moreover, the pictures show the two ends of the loop touching each other, thus physically preventing any further closure; the orthogonality between the LPI and the prosthesis is not preserved. In the fourth specimen there are no loop deformations, but large non-adhesion areas are present along the entire circumference. The non-contact zone on the lateral side of the incus is large enough to view the LPI through it. Significantly, the prosthesis has a purely partial contact with the incus in two points. However, the contact proves to be absolutely fictitious as the prosthesis changes its inclination, following the movements of the SEM plate; the prosthesis loop tends to slip towards the thinner part of the LPI. The mean loose zone measures 85.56 mm (maximal span 110.00 mm) (Table 1) (Fig. 4). 3.2.2. K-Piston-Titanium It appears to be correctly anchored to the LPI, with an average length of 1.31 mm from the umbo and well positioned into the small fenestra of the stapes footplate. The loops of the nine prostheses show oval deformations especially in lateral–medial view; both ends often touched each other, making further closure impossible without heavier deformations. This is more evident on the anterior–posterior view. The prosthesis results to be firmly

attached to the anterior and posterior sides of the LPI, but shows a blank zone on the lateral side. The mean loose zone measures 177.36 mm (maximal span 262.00 mm) (Table 2 and Fig. 4). At higher magnification, the surface of the prosthesis appears rougher and more porous than the platinum piston. The orthogonality between the LPI and the prosthesis is not preserved. The use of the McGee forceps for the crimping caused the loss of the spiral shape of the band in all but one case. This case shows a LPI extremely thin but not malformed; consequently, no crimping can be achieved. On the medial side of the incus, a notch caused by the free end of the loop during crimping is appreciable. 3.2.3. a`Wengen Clip piston It appears to be correctly inserted with an average length of 1.38 mm and well positioned into the opening of the stapes footplate. Given the natural inclination of the incus, the perpendicularity between piston and LPI is not achieved, whereas it is preserved between the piston and the footplate, as in the case of the other prostheses (Fig. 5). The piston does not present any deformation. The piston is correctly clipped in its central portion. The interface between the LPI and the lateral arch of the prosthesis shows contact only at the extremities, leaving a central area of

Table 1 Richard’s piston: measuring results. Richards piston Sample

Distance from the LPI tip (mm)

Max empty spaces lateral aspects (mm)

Kind of deformation

Orthogonality with LPI

Loop’s ends contact

1 2 3 4 5 6 7 8 9 10 Mean Min Max SD

1.37 1.26 1.44 1.57 1.36 1.37 1.41 1.35 1.40 1.38 1.39 1.26 1.57 0.114673

96.70 83.40 110.00 67.20 70.50 82.50 86.30 84.90 92.10 79.90 85.56 67.20 110.00

Oval Oval Oval No Oval Oval Oval Oval Oval Oval

No No No No No No No No No No

Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes

LPI: long process of incus and SD: standard deviation.

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Fig. 4. SEM study. Richards1 Platinum-Teflon piston (a and b): the oval shape deformation of the loop is clearly visible; there is a wide hollow space on the lateral aspect of the LPI and there is tight contact only on the anterior and the posterior aspects. K-Piston-Titanium (c and d): the oval deformation with lost of the spiral shape and contact only with anterior and posterior aspects are evident.

hollow space (Fig. 6). The mean loose zone measures 71.71 mm (maximal span 86.13 mm) (Table 3). In the anterior–posterior view it is all the more clear that only the upper edge of the band touches the incus. On the other hand, in the same projection, the prosthesis reaches the medial portion of the LPI extremely well.

footplate, orthogonal with the footplate but not with the incus; there are no deformations. As shown both in the inferior–superior view and in the posterior–anterior projection, the prosthesis achieves a homogeneous and regular contact along most of the LPI circumference. The loop leaves very few empty spaces. The mean loose zone measures 23.10 mm (maximal span 25.70 mm) (Table 4) (Fig. 6). In the anterior–posterior view the two ends of the hook clearly do not come in contact and, moreover, they result to be slightly asymmetrical.

3.2.4. SMart Nitinol-Teflon piston It appears crimped at 1.35 mm as the mean distance from the LPI tip, correctly positioned into the opening of the stapes Table 2 K-piston: measuring results. K-Piston-Titanium Sample

Distance from the LPI tip (mm)

Max empty spaces lateral aspects (mm)

Kind of deformation

Orthogonality with LPI

Loop’s ends contact

Spiral shape maintenance

11 12 13 14 15 16 17 18 19 20 Mean Min Max SD

1.25 1.44 1.16 1.25 1.27 1.34 1.36 1.41 1.28 1.45 1.31 1.16 1.45 0.07746

262.00 130.62 175.00 116.00 164.00 169.20 189.50 175.90 180.70 203.17 177.36 116.00 262.00

No Oval Oval Oval No Oval Oval Oval No Oval

No No No No No No No No No No

No Yes Yes Yes Yes No Yes Yes Yes Yes

Yes No No No No No No No No No

LPI: long process of incus and SD: standard deviation.

Fig. 5. SEM study. Titanium a`Wengen1 clip-piston (a) and Nitinol-Teflon SMart1 piston (b). The perpendicularity between pistons and LPI is not achieved given the natural inclination of the incus (axes). The two ends of Nitinol-Teflon SMart1 piston do not reach any contact.

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Fig. 6. SEM study. Titanium a`Wengen1 clip-piston (a and b): the prosthesis reaches well the medial aspect of the LPI (a). It is clearly displayed how the lateral arch of the prosthesis takes contact only at the extremities and, precisely, in its upper edge with a wide central hollow space (b). Nitinol-Teflon SMart1 piston (c and d): the prosthesis appears correctly positioned (c). The contact zones appear to be more homogeneous along most of LPI circumference with few empty spaces (arrow). The loop surrounds approximately 80% of LPI. The shape memory of nitinol self-limits the closure (d).

3.3. Comparative morphological study The four types of prostheses appear to be anchored to the LPI, with a variable distance from the umbo of eardrum, to 1.31 mm (Kpiston) from 1.39 mm (Richards piston). While almost all loops of Richards pistons and K-PistonTitanium prostheses show oval deformations (Fig. 4), the a`Wengen Clip pistons and SMart pistons do not present any deformation. Because of the natural inclination of the incus, the perpendicularity between the four types of prostheses and LPI is not achieved, whereas it is preserved between all prostheses and the footplate (Fig. 5).

The SMart piston is the only prosthesis that achieves a homogeneous and regular contact along most of the LPI circumference, with very few empty spaces between the loop and the incus (in the maximal span, 25.70 mm) (Fig. 6); Richards pistons, K-titanium-pistons and a`Wengen Clip pistons show large non-adhesion areas and loose zones with variable significant measures (in their maximal span, 110 mm for Richards pistons, 262 mm for K-pistons and 86.13 for a`Wengen Clip pistons) (Tables 1–4). Because of the use of the McGee forceps for the crimping, the surface of the loop of the Richards piston shows the marks of the microforceps and the K-piston presents the loss of the spiral shape

Table 3 a´Wengen Clip piston: measuring results. a´Wengen Clip piston Sample

Distance from the LPI tip (mm)

Empty space lateral aspects; anterior edge (mm)

Kind of deforma-tion

Orthogonality

21 22 23 24 25 26 27 28 29 30 Mean Min Max SD

1.43 1.15 1.46 1.33 1.53 1.49 1.28 1.39 1.36 1.37 1.38 1.15 1.53 0.147309

52.41 86.13 73.88 77.00 69.11 66.98 74.21 75.19 67.87 73.06 71.71 52.41 86.13

No No No No No No No No No No

No No No No No No No No No No

LPI: long process of incus and SD: standard deviation.

Table 4 SMart piston: measuring results. SMart piston Sample

Distance from the LPI tip (mm)

Empty spaces lateral aspects (mm)

Kind of deformation

Orthogonality

Loop’s ends contact

Spiral

31 32 33 34 35 36 37 38 39 40 Mean Min Max SD

1.38 1.36 1.28 1.42 1.31 1.36 1.29 1.31 1.37 1.34 1.35 1.28 1.42 0.055678

21.20 22.30 23.80 22.50 25.70 24.90 22.80 23.00 25.10 19.90 23.10 21.20 25.70

No No No No No No No No No No

No No No No No No No No No No

No No No No No No No No No No

Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes

LPI: long process of incus and SD: standard deviation.

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of the band. Moreover, in these types of pistons both ends of the loop often touch each other, making further closure impossible without heavier deformations. 4. Discussion In the stapes surgery three main goals have been singled out in order to achieve the correct anchorage of prosthesis and as better as possible sound transmission: reducing the difficulty of the opening of the stapes footplate, facilitating the positioning of the prosthesis and standardizing the effectiveness of crimping to the LPI. Positioning is usually tested with a manual yet empiric manoeuvre by touching the anchored loop with a 458-hook. However, the most effective tool, in vivo, may be the Laser Doppler Vibrometry [8] or a Piezoelectric Ceramic Device [9]. Crimping is considered one of the most difficult and dangerous surgical step and it can induce the most important complications (erosion of LPI, LWS, sensorineural hearing loss). Several authors have reported that malfunctioning of the incus–prosthesis interface is the most frequent reason for revision surgery (40–53%). The most common ossicular abnormality is the incus erosion (23.5–69%) [10–14]. Different theories have reported the possible cause of erosion and necrosis of LPI. It was assumed that if the wire loop is not crimped to the incus firmly enough, the vibration between incus and stapedial prosthesis led to a notching of LPI with a consecutive further loosening of the wire loop, causing failure of the initial hearing improvement [15]. Marquet suggested a correlation between the wire of the piston, regarded as a ‘‘cutting tool’’, and the necrotic evolution of the LPI; as a matter of fact, it is not only the small contact surface of the wire to induce over-tightening, but also – and above all – the subjective crimping manoeuvre that can be more or less strong [16]. The reduction of blood supply could lead, in the long run, to the development of a gradual erosion and a necrosis of the lenticular process [17]. Other authors, however, demonstrated an extremely rich anastomotic vascular tree between the mucosal and medullar vessels of LPI. Erosion of LPI and LWS could be ascribable more often to poor loop contact rather than to devascularization from over-crimping [18–20]. A comparison between a teflon-wire piston and a gold piston in two operations by means of SEM studies led to the hypothesis that the winding grooves in the surface of the teflon shaft together with impaired middle ear mechanics were the main causes of a scar being contracted in the direction of the oval window with resulting necrosis of the incudal process [21]. In a recent retrospective study, Schimanski highlighted specific findings correlated to certain prostheses: teflon-platinum prosthesis causes necrosis or erosion of the LPI in 69% and gold piston causes reparative granuloma sometimes combined with necrosis of the incus in 70% of cases. There are no specific diagnostic finding with titanium or nitinol pistons [13]. Prostheses with a round cross-section (e.g., wire) may become injured in the application site of the incus because of a higher contact pressure of the small contact area in comparison with a band contact [22–24]. Further hypotheses implicate toxic and inflammatory foreign-body reactions in the LPI, which has a relatively poor blood flow anyway [25]. In order to reduce the malcrimping-related complications and to realize the most effective contact between the prosthetic loop and the LPI, many authors have studied every single part of the stapedial prosthesis [26,27]. The goal of the technological research is to plan and produce the prostheses with the most suitable material in terms of malleability, stiffness and biocompatibility. The four prostheses considered in the present study show some differences: the loop of three prostheses is in titanium and only one is in platinum. Both materials proved to be highly biocompatible but the titanium is considered the gold standard material because its roughness assures better connection with the surrounding

tissue. Moreover, the variability of the cross-section of the incus at the piston’s attachment site was demonstrated [28,29]. In this morphological study, the band-shape loops of the K-piston and the Richards piston are too long compared to the LPI circumference (2.46  0.23 mm): in these two groups, 90% of the prostheses appear deformed. Consequently, wide areas of the loop have no contact with the ossicular surface. There is tight contact only on the anterior and the posterior aspects of the LPI (Figs. 4 and 7). There is a common agreement about the physical dynamics of sound transmission through the ossicular chain: the more homogeneous is the contact of prosthesis with LPI, the biggest is the amount of transmission force. Considering that the physiological vibration of the incus rotates around an axis running through the anterior malleolar ligament and the short process of the incus (or slightly superiorly) [30], it is evident that the anterior and posterior sides are not the proper anchoring sites to obtain the most effective sound transmission. Although both pistons achieve a solid connection with the LPI, there is no assurance of longlasting reliability of this questionable anti-vectorial joint (Fig. 7), especially after tympanic displacements following barometric variations (up to 1 mm). On the contrary, the a`Wengen prosthesis clings to the medial and lateral sides of the LPI, which are more effective in terms of vibrational dynamics. The ‘‘clip system’’ is the main strong point of this prosthesis because it exploits the vectors of vibrating force and reduces the unpredictability of crimping. At the same time, it is its weak point because it concentrates only in few points the exerted force on the bone (Figs. 5 and 6). The band-shaped and, in particular, the a`Wengen prostheses examined by means of Operative Microscopy seem to present a broader contact area then the wire-shaped ones, but at higher magnification (SEM) it is striking to observe how these loops often act like wire loops. This is due to the fact that the lower extremity of the incus is steeper towards the medial aspect of the middle ear and therefore the LPI is not parallel to the stapes footplate. In order to maintain the orthogonal axis between the piston and the footplate, unless the prosthesis is deformed, it is quite difficult that the loop touches the incus surface along the entire width of the band shape prosthesis; so, the contact is limited essentially to the upper edge (Fig. 8). The SMart piston has demonstrated the most unvarying and regular contact, homogenously surrounding approximately 80% of

Fig. 7. The contact areas on the anterior and posterior aspects of the LPI are not the most effective sites of contact considering the physiological vibration pattern (especially at the lower frequencies) whose vectors drive perpendicularly towards the vestibule and to the opposite direction.

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Fig. 8. The band-shape prostheses often act like wire loops due to the fact that lower extremity of the incus is steeper towards the medial wall of the middle ear cleft than upper extremity (b). Therefore the LPI is not parallel to the footplate how, instead, ought to be the ideal anatomical alignment (a). For this reason it is very difficult for a bandshape loop to touch the LPI surface along the entire width without loosing the orthogonality (c).

the LPI, with sporadic and narrow hollow spaces along the entire length of its crimping. The shape memory of nitinol alloy makes the loop (Ø 120 mm) self-limiting the closure thus avoiding strangling. Another advantage of the SMart piston is that the thermal crimping does not need any further mechanical manoeuvre and it reduces risks of iatrogenic damage to the ossicular chain and to the inner ear by minimizing manipulation of the prosthesis. Moreover, the slightly asymmetrical shape of the nitinol piston, preserved after thermal crimping, allows the loop to fit every size of LPI and distributes the pressure forces over different planes; on the contrary, the spiral shape of the K-piston is sometimes lost when the crimping is manual using the McGee forceps. However, in the literature some limitations to this prosthesis have been described. The heat application necessary for crimping also may damage the mucosa, the mucoperiosteum and the bone of the incus. Furthermore, nickel may potentially cause a toxic or allergic reaction because up to 16% of the population have an allergy to nickel. There have been no reported experimental results concerning the toxic reactions of middle ear structures to nickel and the role of nickel as an allergen in the middle ear. Only one case of sensorineural hearing loss and development of gray exudation in the middle ear after stapedotomy using a nitinol prosthesis is reported [31,32]. With regard to clinical outcomes, in a preliminary study we have shown that use of the SMart self-crimping shape-memory nitinol stapes piston may eliminate drawbacks of manual crimping in stapedotomy in patients with otosclerosis, allowing more reliable and consistent airbone gap closures [7]. During the last years several authors [23,33–38] have demonstrated that tight fixation, as provided by nitinol prostheses, leads to improved functional results because of better sound transmission properties at the incus–prosthesis interface. In patients undergoing stapedotomy using the nitinol stapes piston, Rajan demonstrated significantly smaller postoperative airbone gaps compared to the control group (patients undergoing conventional titanium piston stapedotomy) [33]. Huber founded an improvement in airbone gap closure in the range of 3 dB pure-tone average and more pronounced at higher frequencies [23]. Recently Mangham outlined the significantly better low-frequency hearing results with nitinol stapes prosthesis [38]. These studies are limited by small patient numbers and collection of only short-term hearing results. Further research is required on the potential benefits of application of the nitinol piston in stapes surgery for otosclerosis. 5. Conclusions The attachment site of a stapedial prosthesis to the LPI plays a key role in the success of the hearing gain in stapes surgery. Because of the irregular profile of the incus at the attachment site

of the stapedial prosthesis, a complete adhesion of the prosthetic loop cannot be obtained. An ideal stapedial prosthesis should allow a suitable coupling with the ossicular chain, avoiding during the surgical procedure any iatrogenic damage to the ossicles and the inner ear and achieving a good and long-lasting sound transfer. Consequently, on the basis of the morphological analysis with SEM, in the surgical practice, the preference could be given to the ‘‘new generation’’ stapedial prostheses that achieve greater contact such as the self-retaining and the thermal crimping pistons (a`Wengen and SMart) compared to the standard sized prostheses considered. Conflict of interest None. Acknowledgements The authors thank Dr. Claudio Furlan CUGAS – University of Padua, Italy, for his assistance and scientific contribution in performing the SEM study and Dr. Roberta Favaron and Dr. Cristina Ferri for their linguistic assistance. References [1] Lesinski SG. Revision stapedectomy. Curr Opin Otolaryngol Head Neck Surg 2003;11:347–54. [2] Szyman´ski M, Goła˛bek W, Morshed K, Siwiec H. The influence of the sequence of surgical steps on complications rate in stapedotomy. Otol Neurotol 2007; 28:152–6. [3] Kwok P, Fisch U, Strutz J, May J. Stapes surgery: how precisely do different prostheses attach to the long process of the incus with different instruments and different surgeons? Otol Neurotol 2002;23:289–95. [4] Gibbin K. The histopathology of the incus after stapedectomy. Clin Otolaryngol 1979;4:343–54. [5] Huber AM, Ma F, Felix H, Linder T. Stapes prosthesis attachment: the effect of crimping on sound transfer in otosclerosis surgery. Laryngoscope 2003;113: 853–8. [6] Skinner M, Honrado C, Prasad M, Kent HN, Selesnick SH. The incudostapedial joint angle: implications for stapes surgery prosthesis selection and crimping. Laryngoscope 2003;113:647–53. [7] Babighian G, Fontana M, Caltran S, Ciccolella M, Amadori M, De Zen M. The heat-activated stapes prosthesis SMart piston: technique and preliminary results. Adv Otorhinolaryngol 2007;65:190–6. [8] Vogel U, Zahnert T, Hoffmann G, Offergeld C, Hu¨ttenbrink K-B. Laser vibrometry of the middle ear: opportunities and limitations. In: Hu¨ttembrink K-B, editor. Middle ear mechanics in research and otosurgery. Baalsdorf, PA: UniMedia GmbH; 1997. p. 128–33. [9] Kiyofumi G, Hidemitsu S, Hiroshi A, Shinsei N, Shingo M. Measurement of the stapes mobility and cochlear input impedance using a newly developed piezoelectric ceramic device. In: Hu¨ttenbrink K-B, editor. Middle ear mechanics in research and otosurgery. Baalsdorf, PA: UniMedia GmbH; 1997. p. 191–6. [10] Vincent R, Rovers M, Zingade N, Oates J, Sperling N, Deve`ze A, et al. Revision stapedotomy: operative findings and hearing results. A prospective study of 652 cases from the Otology–Neurotology Database. Otol Neurotol 2010;31: 875–82. [11] Gros A, Vatovec J, Zargi M, Jenko K. Success rate in revision stapes surgery for otosclerosis. Otol Neurotol 2005;26:1143–8.

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