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

Titanium middle ear (ME) prostheses are widely used in surgical practice due to their acoustic properties. However, they present a significant drawback shared by all synthetic materials currently in use for ME reconstruction: they can be rejected by the organism of the host. In this study, we aim to review the current literature on titanium partial ossicular replacement prostheses (PORPs) and total ossicular replacement prostheses (TORPs) extrusion and dislocation. Eighty articles were analysed after a full article review based on the inclusion and exclusion criteria. The most common indication for reconstruction was chronic otitis media with cholesteatoma. The average extrusion or dislocation rate was 5.2%, ranging from 0 to 35%. The average improvements in the air–bone gap were 12.1 dB (1.6 dB to 25.1 dB) and 13.8 (−0.5 dB to 22.7 dB) for the PORP and TORP groups, respectively. The data reported on this topic are highly variable, demonstrating that functional outcomes are difficult to predict in clinical practice. We believe that the current limitations could be overcome with technological developments, including bioengineering research focused on promoting prosthesis adaptation to the ME environment.


Introduction
The restoration of hearing conduction entwined within the eradication of middle ear (ME) pathologies represents an outstanding goal of modern otosurgery.Ossiculoplasty (OPL) is a surgical technique employed to restore conductive hearing loss by replacing the defective ossicular chain, of which the history dates back to the 1950s.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 because of the high biocompatibility [1].The most commonly used autograft material has been the reshaped incus body, although its usage is limited by the lack of availability in diseased ME, the risk of residual cholesteatoma, and the possible fixation to the walls of the ME.Until 1987, homograft implants processed from cadavers were in use and then abandoned due to the potential risk of infection [2].Nowadays, bioengineering products from decellularized banked cortical bone are being explored [3].In the last three decades, many alloplastic materials have been tested as suitable ossicular replacements, such as metals, ceramics, and plastics [2].Depending on the defects to be reconstructed, synthetic prostheses are distinguished between partial ossicular replacement prostheses (PORPs), mounted on the intact stapes, and total ossicular replacement prostheses (TORPs) for cases with no stapes superstructure [4].
Brain Sci.2023, 13, 1476 2 of 16 Since the 1990s to date, technologies that bypass the ME sound-conducting mechanism have spread within the market [5,6]; however, passive ME implants continue to be widely used and studied.At present, titanium is widely being used for its physical properties, being lightweight with high stiffness and allowing for easy individual adaptation to anatomical variations.Moreover, it is safe during magnetic resonance imaging both at 1.5 and 3 tesla, which could be necessary for the depiction of recuring cholesteatomas [7].In current literature, numerous studies focus on the hearing outcomes with titanium prostheses, demonstrating the reliably of this material in restoring the conduction mechanism [8,9].In a recent meta-analysis, Kortebein et al. reported a rate of 70.7% PORP and 57.1% TORP patients with a postoperative ABG less than 20 dB [8].Otherwise, in our opinion, the rate of complications to be expected represents a notable aspect of presurgical counselling, of which the available data are controversial.
We aim to review existing literature about the complications of titanium prosthesis ossicular reconstruction, with particular regard to extrusion and dislocation, and discuss the current clinical perspectives.

Materials and Methods
A search of the literature was performed using the PUBMED database.The strategy used was based on the "Preferred Reporting Items for Systematic Reviews and Metaanalyses" (PRISMA) guidelines.The research was conducted using the following keywords: "((TORP) OR (PORP) OR (ossicular replacement) OR (ossiculoplasty)) AND titanium".The search was conducted in June 2023.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.Only articles in English were included.Review articles, letters, editorials, and case reports were omitted.The exclusion criteria also applied to animal research and cadaver studies.In the included articles, we considered postoperative improvement in the air-bone gap (ABG) as a secondary outcome.Two reviewers performed study selection independently and screened all the retrieved titles and abstracts.The differences in assessment for analysis were resolved with assistance from a third assessor.A final selection of the articles for granular analysis was then made by the-above-mentioned two reviewers.The data extraction was performed by four authors.The extracted data were recorded in pre-developed tables in MS Excel and Word.

Results
A PRISMA flow chart illustrating both the search numbers and included studies is schematically presented in Figure 1.A total of 311 records were 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 a full-text review, of which 42 did not meet the inclusion criteria, and 5 additional records were excluded because the full text was unavailable.Eighty articles were included in the review and were further analysed.The selected articles covered 7117 subjects and 7214 ME implants, including 3554 PORPs and 3660 TORPs.The demographic characteristics are displayed in Table 1.In six studies, the average age was less than 18 years.The most common indication for reconstruction was chronic otitis media (5829 cases, 80.8% of the total sample), with mention of cholesteatoma in 2462 cases (42.2%).The surgical details and functional outcomes are shown in Table 2.The complication rate is claimed to be 0% in 18 articles.The average extrusion or dislocation rate was 5.2%, 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.The mean follow-up time was less than or equal to 12 months in 30 studies, among which 24.8% of the complications were reported.Their management is cited in 33 articles and surgical revision is reported for 219 cases.Regarding technical details, the Brain Sci.2023, 13, 1476 3 of 16 presence or absence of cartilage interposition between the prosthesis and the tympanic membrane is mentioned in 71 articles.When this aspect is addressed, the technique of cartilage interposition is encountered in 92.4% of cases.Prosthesis placements without cartilage protection have been described as a procedural choice for the whole sample in five works.Regarding the staging procedure, in nine articles, the OPL was staged in the whole sample, presenting a complication rate of 6.5%, whereas in 19 works, the OPL was not staged at all, with a complication rate of 2.9%.The average improvement in ABG for PORP was 12.1 dB, ranging from 1.6 dB to 25.1 dB.The average change in ABG for TORP was 13.8 (from −0.5 dB to 22.7 dB).
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.The mean follow-up time was less than or equal to 12 months in 30 studies, among which 24.8% of the complications were reported.Their management is cited in 33 articles and surgical revision is reported for 219 cases.Regarding technical details, the presence or absence of cartilage interposition between the prosthesis and the tympanic membrane is mentioned in 71 articles.When this aspect is addressed, the technique of cartilage interposition is encountered in 92.4% of cases.Prosthesis placements without cartilage protection have been described as a procedural choice for the whole sample in five works.Regarding the staging procedure, in nine articles, the OPL was staged in the whole sample, presenting a complication rate of 6.5%, whereas in 19 works, the OPL was not staged at all, with a complication rate of 2.9%.The average improvement in ABG for PORP was 12.1 dB, ranging from 1.6 dB to 25.1 dB.The average change in ABG for TORP was 13.8 (from −0.5 dB to 22.7 dB).Canal wall down (CWD); canal wall up (CWU); ossiculoplasty (OPL); years (y); months (mo); not available (n.a.).Data included in the column "surgery" refer to the procedure performed at the time of the ME implant positioning, regardless of any previous surgery.In the column "cartilage", we included the case in which cartilage interposition between the prosthesis and the tympanic membrane was cited.In the column "staging", we reported, when available, the number of ossicular reconstruction performed in a second-stage procedure.
In the columns "preoperative ABG (pre-op ABG)" and "postoperative ABG (post-op ABG)", n.a.indicates that this outcome is not mentioned or audiometric results differentiated between the PORP and TORP groups are not available."Extrusions and dislocations/ears (%)": we excluded extrusions and dislocations caused by cholesteatomas.The data included in the columns "Onset" and "Treatment" refer to the time of appearance and management of complications."Follow-up" indicates the average follow-up or, when not available, its range.

Discussion
OPL is a well-established surgical procedure intended for auditory rehabilitation; however, its practical use collides with some technical issues still today.An ideal OPL prosthesis should ensure hearing restoration, along with being safe and stably integrated into surrounding tissues.Titanium has proven to be a reliable material in terms of easy surgical manipulation and functional hearing results [8].However, it is not free of postoperative complications, such as dislocation or extrusion, along with non-titanium prostheses [39].Unfortunately, the literature regarding titanium complication rates is often conflicting.We strongly believe the fragility of evidence about this topic could hinder both the therapeutic choice and the preoperative counselling.To our knowledge, this is the first work that specifically analyses the existing data about titanium TORP and PORP extrusion and dislocation rates.In their review, Kortebein and colleagues have addressed this issue.However, they focused on articles presenting at least one audiometric outcome, with a 12-month minimum follow-up, thus limiting the available data about complications [8].On the other hand, with the present work, we provided a comprehensive overview of this topic, considering functional auditory data in the background.We considered the rate of extrusion and dislocation for combined PORPs and TORPs because only a 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, 24.8% of the overall complications occurred in studies with a mean follow-up time of less than or equal to 12 months.Only a few studies reported the onset time, thus allowing for 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 evaluation focused on the six paediatric studies disclosed an increased complication rate in this cohort (13.7%) when compared to the overall results (5.2%).Unfortunately, in the studies reporting cohorts composed of both adults and children, the age of patients who underwent extrusion or dislocation is not specified, precluding a fair comparison of complication rates by age.However, we can speculate, as suggested by Michael and colleagues, that the higher frequency of eustachian tube dysfunction and air way inflammation in the pediatric population could explain the greatest incidence of complications [28].On the other hand, 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 the staging of treatment.Regarding surgical techniques, the staging procedure could be expected to ensure a more stable ME environment and limit complications.However, our data did not reflect this trend, confirming that many variables are involved in functional results.Furthermore, many authors claim that a piece of cartilage should be placed between the head of the titanium prosthesis and the tympanic membrane in order to prevent extrusion and ameliorate acoustic transfer [41,42].The supporters of this technique believe that the use of cartilage would enhance the adaptation of the prosthesis to the inclination of the tympanic membrane, minimize recurrence of tympanic retraction, and avoid inflammatory reaction due to direct contact with the metal.On the other hand, according to other studies, the cartilage interposition is not essential [17,50].In our systemic review, prosthesis placement without cartilage protection have been described as procedural choice for the whole sample in five articles, declaring an extrusion rate of 0%, 6.8%, 7.5%, 10%, and 23.8%, respectively (see Table 2).These data are overwhelming to interpret, even considering that the reported extrusion or dislocation rate was 0% in 18 articles overall.It can be argued that the complete absence of complication sounds unrealistic.This number is almost certainly under-reported, or the follow-up interval was too short (less than or equal to 12 months in 10 of these studies).In addition, in our analysis, we considered the preoperative and postoperative ABG as a secondary outcome, despite the presence of these data not being among the 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 [8].We disclosed a high variability in the average Brain Sci.2023, 13, 1476 13 of 16 ABG improvement among the studies included in the present review.It should be noted that 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 information about extrusions and dislocations treatment is 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 active ME prostheses.The average ABG improvement was 12.1 dB, ranging from 1.6 dB to 25.1 dB, for the PORP group, and 13.8 dB, from −0.5 dB to 22.7 dB, for the TORP group.The functional results depend on many factors, including the status of the ME environment and eustachian tube dysfunction.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 OPL outcomes.Furthermore, patients should be aware that despite their satisfying audiologic results, titanium PORPs and TORPs 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 for a non-reinforced transmission of incident sound waves [86].In fact, they entail certain anatomical and functional prerequisites that limit their use to selected situations [4].Currently, active ME prostheses, as well as percutaneous or transcutaneous bone conduction implants, have been designed to overcome the abovementioned issues [4,5].Nevertheless, 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: whether to shelve the experience of titanium prostheses or strive to overcome their ME adaptability and functional limits, perhaps with bioengineering tools?

Conclusions
Here, we present a comprehensive literature review focused on titanium TORP and PORP extrusion and dislocation.We believe that the variability in the reported complication rates demonstrates that the factors involved in determining the prosthesis' adaptability in ME are highly changeable and difficult to predict.In our opinion, these considerations should be an integral part of preoperatory counselling.Moreover, we advocate that further research that using current technology could overcome the existing limits of titanium ME PORPs and TORPs to exploit their advantage in clinical practice.

Figure 1 .
Figure 1.PRISMA 2020-based flow diagram showing the review search.

Figure 1 .
Figure 1.PRISMA 2020-based flow diagram showing the review search.

Table 1 .
Demographics and clinical data.

Table 2 .
Surgical details and functional outcomes.