The Issue of Extrusion and Dislocation in Titanium Middle Ear Prostheses: A Literature Review

1. Introduction

The restoration of hearing conduction entwined within the eradication of middle ear (ME) pathologies represent an outstanding goal of modern otosurgery. Indeed, with the demands of today’s fast paced society based on communication and rapid interactions, adequate social hearing is essential. As is well known, hearing loss leads to communication difficulties and social isolation. In addition to this, effortful listening increases energy required for processing and comprehending the auditory signal, thus diverting cognitive resources from other mental tasks[1]. Historically, the disadvantages of monaural compared with binaural hearing have not been stressed in audiological debate. Otherwise, current literature agrees hearing rehabilitation involves restoration of binaural stimulation. Indeed, central auditory pathway combine and compare the raw information from the two cochleae addressing complex tasks such as sound localization and speech perception in demanding listening environments[2]. While, since the 1990s to date technologies which bypass the ME sound-conducting mechanism have spread onto the market[3]^,[4], ossiculoplasty and passive ME implants continue to be widely used and studied. Several materials and techniques have been adopted over the years for ossicular reconstruction, with varying degrees of success. When available, autologous material refashioned to provide customized interposition is the prime source of repair[5]. In the last three decades, many alloplastic materials have been tested as suitable ossicular replacements, such as metals, ceramics, and plastics. Depending upon the defects to be reconstructed, synthetic prostheses are distinguished between Partial Ossicular Replacement Prostheses (PORP), mounted upon the intact stapes, and Total Ossicular Replacement Prostheses (TORP) for cases with no stapes superstructure[6]. At the present time, titanium is widely used for its physical properties, being lightweight with high stiffness and allowing easy individual adaptation to anatomical variations. In current literature numerous studies focus on hearing outcomes with titanium prostheses, demonstrating the reliably of this material in restoring conduction mechanism[7]. On the other hand, the rate of complications to be expected represent a notable aspect in presurgical counselling, regarding which the reported data are often conflicting. We aim to review the existing literature about complications of titanium prostheses ossicular reconstruction, with particular regard to extrusion and dislocation, and to discuss the current clinical perspectives.

2. Materials and Methods

A search of the literature was performed in the PUBMED database. The strategy used was based on the “Preferred Reporting Items for Systematic Reviews and Meta-analyses” (PRISMA) guidelines. The research was conducted using the following keywords: “((TORP) OR (PORP) OR (ossicular replacement) OR (ossiculoplasty)) AND titanium”. The population of interest was patients who had undergone ossiculoplasty with titanium PORP or TORP. There was no limitation in age, sex, or follow-up periods. The studies also had to include data about complications, namely prosthesis extrusion or dislocation focusing on cases not related to recurrence of cholesteatoma. Only articles in English were included. Review articles, letters, editorials and case reports were omitted. Exclusion criteria also applied to animal research and cadaver studies. In the included articles we considered the postoperative improvement in air-bone gap (ABG) as a secondary outcome.

3. Results

A PRISMA flow chart illustrating both the search numbers and included studies is schematically presented in Figure 1. A total of 311 records ware identified. However, after excluding articles written in languages other than English, editorials, letters to editors, case reports, and reviews, 243 studies were considered. A preliminary selection was based on titles and abstracts: 127 papers were evaluated for full text review, of which 41 did not meet the inclusion criteria and 5 additional records were excluded because the full text was unavailable. 81 articles were included in the review and were further analysed. The selected articles covered 7269 subjects and 7366 ME implants, including 3638 PORP and 3728 TORP. The demographic characteristics are displayed in Table 1. In 6 studies the average age was less than 18 years. The most common indication for reconstruction was chronic otitis media with cholesteatoma (CCOM, 34,1%), followed by chronic otitis media without cholesteatoma (COM, 16,2%). The indication was generically expressed as chronic otitis media in 2300 cases. Surgical details and functional outcomes are shown in Table 2. The average improvement in ABG for PORP was 12.3 dB, ranging from 1.6 dB to 25.1 dB. The average change in ABG for TORP was 13.7 (range from -0,5 dB to 22.7 dB). The average extrusion or dislocation rate was 5.1% (reported in 62 articles) ranging from 0 to 35%. Considering the six articles in which the average age was less than 18 years, the extrusion or dislocation rate in this limited cohort was 13.7%. The onset of complications is mentioned in only 16 articles, ranging from 2 months to 8 years. Their treatment is cited in 32 articles, in all cases except one the management consisted of surgical revision. The mean follow-up time was less than or equal to 12 months in 30 studies, among which the 25.4% of complications were reported.

4. Discussion

Considering the cognitive and psychosocial impact of hearing loss, its treatment is mandatory not only to restore the auditory perceptual skills but also to ameliorate the central management of cognitive resources[86]. In recent years, the interaction between hearing and cognitive processes has been studied through pupillometry. Indeed, pupil dilation response has demonstrated to be an indicator of mental processing load during listening effort[87]. Hence, the rehabilitation of hearing loss seems to be mandatory for optimization of the limited cognitive resource. Ossiculoplasty is a well-established surgical procedure intended to auditory rehabilitation, however its practical use still today collides with some technical issues. The ideal ossiculoplasty prosthesis should ensure hearing restoration as well as being safe and stably integrated into surrounding tissues. Titanium has demonstrated to be a reliable material in term of easy surgical manipulation and functional hearing results[26]. In a recent meta-analysis Kortebein et al. reported a rate of 70.7% of PORP and 57.1% of TORP patients with a postoperative ABG less than 20 dB[7]. Moreover, it is safe during magnetic resonance imaging both at 1.5 and 3 tesla, which could be necessary for the depiction of recuring cholesteatoma[88]. However, it is not free of postoperative complications such as dislocation or extrusion. To our knowledge, this is the first work that specifically analyses the existing literature about titanium TORP and PORP extrusion and dislocation rates. Kortebein and colleagues in their review have addressed this issue. However, they focused on articles presenting at least one audiometric outcome, with a 12-months minimum follow up, thus limiting the available data about complications[7]. On the other hand, with the present work we would provide a comprehensive overview about this topic. It can be argued the exclusion of extrusion or dislocation caused by cholesteatoma from the analysis to be a limit. However, we consider the presence of cholesteatoma in an operated ear a complication itself. Therefore, the decision was taken to avoid a possible misleading factor, focusing on the intrinsic issues of titanium prostheses. Moreover, we considered the rate of extrusion and dislocation for combined PORPs and TORPs because only few articles report complications separated for the two cohorts. Our literature review has demonstrated that the reported extrusion and dislocation rates vary greatly in literature, ranging from 0 to 35%, distributed over variable follow-up time. Interestingly, the 25.4% of the overall complications occurred in studies with mean follow-up time less than or equal to 12 months. The evaluation focused on the 6 paediatric studies has disclosed an increased complication rate in this cohort (13.7%) when compared to overall results (5.5%). We can speculate, as suggested by Michael and colleagues, a possible explanation to be the higher frequency of Eustachian tube dysfunction and of air way inflammation in pediatric population relative to adults[27]. Notably, the exiguity of details about the circumstances in which complications have occurred hampers a proper correlation with possible influencing factors, such as ME pathologies, surgical procedures or staging of treatment. Consistently, very few studies reported the onset time, thus allowing a limited discussion about this topic. The only remark which deserves to be underlined is the considerable variability of these findings, ranging from 2 months to 8 years. The information about extrusions and dislocations treatment are limited, however we found a trend in favour of a surgical revision attempt. Unfortunately, the available data do not allow to trace any cases eventually managed with other rehabilitation strategies, such as the active ME prostheses. In addition, in our analysis we considered the preoperative and postoperative ABG as a secondary outcome, despite the presence of these data was not among inclusion criteria. Our findings are in agreement with those of Kortebein et al., who reported an ABG improvement of 12.1 and 16.7 dB after titanium PORP and TORP placement, respectively[7]. We disclosed a high variability in the average ABG improvement among the studies included in the present review. It should be noted the data presented in literature are widely heterogeneous and thus difficult to compare, with respect to titanium prostheses models, underlying ME diseases, surgical hands and techniques, and follow-up strategies. The average ABG improvement was 12.3 dB, ranging from 1.6 dB to 25.1 dB, for PORP group, and 13.7 dB, from -0,5 dB to 22.7 dB, for TORP group. The functional results depend on many factors including status of the ME environment and Eustachian tube disfunction. According to our review, the most common indication for ossicular reconstruction is represented by chronic otitis media. Indeed, recurrence or progression of the ME pathology can affect the outcomes of ossiculoplasty. Moreover, host tissues are reported to interact with the surface of the ME prosthesis inducing a foreign body inflammation with a possible consequential dislocation and extrusion, thus compromising the initial functional results[89]. We strongly believe these considerations should be integral part of preoperatory counselling. Furthermore, the patients should be aware titanium PORP and TORP, despite their satisfying audiologic results, present the technical limitations shared by all passive ME prostheses. Namely, they aim to restore a normal coupling between the tympanic membrane and the inner ear, thus allowing a non-reinforced transmission of incident sound waves.[90] In fact, they entail certain anatomical and functional prerequisites that limit their use to selected situations.[6] Currently, the active ME prostheses, as well as percutaneous or transcutaneous bone conduction implants, have been designed to overcome the abovementioned issues[6]^,[3]. Otherwise, these solutions imply higher costs and the discomfort of an external component. All in all, current technological developments place us on the horns of a dilemma: to shelve the experience of the titanium prostheses or strive to overcome their ME adaptability and functional limits, maybe with bioengineering tools?

5. Conclusions

Here, we present a comprehensive literature review focused on titanium TORP and PORP extrusion and dislocation. We believe the variability in the reported complication rates demonstrates the factors involved in determining the prostheses adaptability in ME are highly changeable and difficult to predict. We advocate further research that using current technology could overcome the existing limits of titanium ME PORP and TORP to exploit their advantage in clinical practice.