Which is Better for Ossiculoplasty Following Tympanomastoidectomy: Polycel® or Titanium?

Introduction

Tympanomastoidectomy (TM) is the surgical management of chronic otitis media (COM) with or without cholesteatoma. After the surgery, ossiculoplasty can be performed either concurrently with TM or separately as a staged operation.^{1 -5} While TM is for the eradication of disease, ossiculoplasty is used to reconstruct the ossicular chain and improves air conduction (AC) hearing. In ossiculoplasty following the TM surgery, a surgeon should determine the graft material for the reconstruction. Currently, some materials are used in the reconstruction of the ossicular chain. We often use autograft ossicles, the incus most commonly, sculpted to serve as interposition grafts. It is advantageous in availability, biocompatibility, and a low extrusion rate. However, there are concerns in the recurrence of disease, particularly in cholesteatoma, and it is difficult to use when the ossicle is eroded. Thus, the need for synthetic prosthesis emerged and polymers, including porous polyethylene (Polycel®), were used.^6,7 Because it is light, easy to handle, and free of autoimmune reaction, this prosthesis is still applied in the reconstruction.^{8 -11} Then, in the 1990s, titanium prostheses were introduced. ¹² Titanium has ferromagneticity with high biocompatibility and biostability and is useful as a sound conductor because of its light and rigid nature. Titanium prostheses seem to be used more often nowadays.^{13 -19} However, according to the literature comparing the 2 materials, both were effective in hearing outcome; there was no conclusion that either was particularly superior.^{8 -10,20}

Factors that are known to affect the surgical outcome are the presence of stapes suprastructure, types of TM (canal wall up or down), diagnosis (COM, cholesteatoma, or congenital anomaly), the status of the middle ear mucosa, and the Eustachian tube function.^{21 -23} The determination of the graft material is important because it is the only factor that a surgeon can decide arbitrarily, whereas others have already been defined even before the reconstruction. Thus, a study comparing the surgical outcomes in the surgery according to the types of the graft material would be valuable, and the results of the study can help surgeons choose a more appropriate graft material. Moreover, since the studies so far have only been a simple comparison between 2 materials, it would be necessary to control the effects of other factors through multivariate analyses. To overcome the limitations of the previous studies, we performed a multiple linear regression, including almost all the prognostic factors in ossiculoplasty. Finally, we analyzed the effect of the graft material on the surgical outcomes and suggested which type of prosthesis was more appropriate for ossiculoplasty following TM.

Materials and Methods

Results

Polycel® was used as the prosthesis for the surgery in 91 patients, and titanium was used in 130 patients. The percentage of patients whose middle ear space was narrow was higher in the titanium group (20.0% in the titanium group and 9.9% in the Polycel® group, P = .043). The mean age of the Polycel® group was 44.2 ± 14.9 years, and the titanium group was 49.2 ± 14.1 years (P = .011) (Table 1).

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Table 1.

Characteristics of Polycel® and Titanium Group.

	Polycel® (n = 91)	Titanium (n = 130)	P value
Gender			.413 †
Male	40 (44.0%)	65 (50.0%)
Female	41 (56.0%)	65 (50.0%)
Operation side			1.000 †
Right	44 (48.4%)	64 (49.2%)
Left	47 (51.6%)	66 (50.8%)
Age, y	44.2 ± 14.9	49.2 ± 14.1	.011 ‡
Diagnosis			.494 †
COM	37 (40.7%)	59 (45.4%)
Cholesteatoma	54 (59.3%)	71 (54.6%)
Types of mastoidectomy			.120 †
Canal wall up	39 (42.9%)	42 (32.3%)
Canal wall down	52 (57.1%)	88 (67.7%)
Type of ossiculoplasty			1.000 †
PORP	54 (59.3%)	78 (60.0%)
TORP	37 (40.7%)	52 (40.0%)
No ossicular reconstruction at TM surgery	28 (30.8%)	43 (33.1%)	.718 †
Middle ear space
Narrow space	9 (9.9%)	26 (20.0%)	.043 †
Pre- and post-operative hearing, dB
Pre-op ABG	37.1 ± 9.6	34.9 ± 9.6	.062 ‡
Post-ossiculo ABG	32.1 ± 11.3	30.2 ± 11.9	.242 ‡

Abbreviations: ABG, air-bone gap; COM, chronic otitis media; PORP, partial ossicular replacement prosthesis; TORP, total ossicular replacement prosthesis; TM, tympanomastoidectomy.

†

Chi-square test.

‡

Independent t test.

Success Rate of the Ossiculoplasty by Conditions of Previous TM

COM without cholesteatoma showed a 49.0% success rate; additionally, the success rate was 48.8% in COM with cholesteatoma (P = .981). The types of previous TM may affect the surgical results. If CWUM was performed before ossiculoplasty, the rate was up to 65.4%. However, it was 39.3% if patients had undergone CWDM (P < .001). The presence of the stapes head also had an effect on the results. When PORP was inserted, if the stapes suprastructure was preserved, the rate was 56.8%. This was higher than the rate in cases of TORP insertion (37.1%) (P = .004) (Figure 1).

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Figure 1.

The success rate of ossiculoplasty by conditions of previous tympanomastoidectomy (TM).

Postoperative ABG in CWUM

Using PORP, the results were similar between the 2 groups. The ABG of the Polycel® group decreased from 34.8 ± 8.7 to 26.7 ± 11.3 dB (P = .002) and it decreased from 29.6 ± 9.1 to 25.0 ± 14.0 dB in the titanium group (P = .106). The success rate of the surgery was 67.6% for titanium and 64.3% for Polycel® without statistical significance (P = .781). Using TORP, the decrease of ABG was from 40.2 ± 7.5 to 27.3 ± 15.9 dB in Polycel® (P = .024). It was from 32.2 ± 10.1 dB to 20.2 ± 8.8 dB in titanium (P = .035). As the successful rate, the titanium group showed a better outcome than the Polycel® group, 75.0% versus 54.5%, though it was not statistically significant (P = .361) (Figure 2).

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Figure 2.

Changes in the air-bone gap (ABG) at 6 months after the ossiculoplasty with Polycel® or titanium following canal wall up mastoidectomy (CWUM). (A) Partial ossicular replacement prosthesis (PORP) (B) Total ossicular replacement prosthesis (TORP).

Postoperative ABG in CWDM

Using PORP, the ABG of the Polycel® group decreased from 35.8 ± 11.6 to 30.6 ± 10.5 dB (P = .083). The success rates were 42.3% for Polycel® and 52.3% for titanium (P = .420). Using TORP, the ABG of the Polycel® group decreased from 39.4 ± 8.6 to 34.9 ± 10.4 dB (P = .097). It decreased from 39.1 ± 8.6 to 29.6 ± 11.0 dB in the titanium group (P < .001). However, both groups showed a low success rate of 26.9% for Polycel® and 31.8% for titanium (P = .666) (Figure 3).

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Figure 3.

Changes in the air-bone gap (ABG) at 6 months after the ossiculoplasty with Polycel® or titanium following canal wall down mastoidectomy (CWDM). (A) Partial ossicular replacement prosthesis (PORP) (B) Total ossicular replacement prosthesis (TORP).

Factors Affecting the Postoperative Air-Conductive Threshold by Multiple Linear Regression

It was negatively affected by age (B: 0.285; 95% CI: 0.136-0.435), preoperative AC threshold (0.277; 0.082-0.472), preoperative BC threshold (0.499; 0.228-0.770), and narrow middle ear space; if a patient’s middle ear space was narrow, the loss is estimated to be about 6.3 dB (6.346; 1.145-11.547). In contrast, titanium material had a positive effect on the postoperative hearing (−4.772; −8.706-−0.838).

Meanwhile, staged surgery, in which ossiculoplasty is performed after primary TM surgery without ossicular reconstruction, was also attempted. However, this approach did not yield any benefits (Table 2). It is therefore recommended to perform ossiculoplasty and TM simultaneously where possible.

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Table 2.

Factors affecting postoperative air-conductive thresholds (N = 221).

	Multiple linear regression † (R2 = 0.461)
Variables	B	95% confidence interval	P-value
(Constant)	13.035	3.436-22.635	.008
Age	0.285	0.136-0.435	<.001
Preoperative AC threshold	0.277	0.082-0.472	.006
Preoperative BC threshold	0.499	0.228-0.770	<.001
Narrow middle ear space	6.346	1.145-11.547	.017
Prosthesis (titanium)	−4.772	−8.706-−0.838	.018

Note. “Gender,” “absence of stapes suprastructure (TORP),” “types of TM operation (CWDM),” and “no ossicular reconstruction at the previous TM surgery” were initially included as variables but excluded by the stepwise method.

Abbreviations: AC, air conductive; BC, bone conductive; CWDM, canal wall down mastoidectomy; TM, tympanomastoidectomy; TORP, total ossicular replacement prosthesis.

†

Multiple linear regression was used to assess factors affecting the postoperative AC thresholds.

Discussion

The management of COM aims to decrease the pathologic lesions in the tympanic and mastoid cavities, thereby reducing otorrhea and improving hearing. For this purpose, surgical treatment is often unavoidable. The goal of middle ear surgery is to eradicate the lesion sufficiently, improve the aeration of the middle ear space, and reconstruct the tympanic membrane. In addition, improvement in the hearing function is also the purpose of the surgery, and it can be achieved by ossiculoplasty that reconstructs eroded ossicular structures. Traditionally, ossiculoplasty was performed as a staged operation approximately 6 to 24 months after TM without ossicular reconstruction.^1,2 However, the staged operation did not guarantee better outcomes; it has been accepted that a one-stage operation that performed ossicular reconstruction concurrently with TM can be effective.^3,4 In the multivariate analysis of this study, we confirmed that the intended 2-staged operation did not affect the outcome of ossiculoplasty.

It has been known that PORP generally shows better outcome than TORP in audiological outcomes.^26,27 This is because PORP that covers the suprastructure of stapes may be advantageous in the stability of the ossicular chain and sound conduction. In our study, hearing outcomes after ossiculoplasty following CWDM were better in PORP than in TORP. In CWUM, on the other hand, titanium materials showed more favorable results in TORP than in PORP (Figure 2). It was interesting; however, the authors concluded that it would not be appropriate to interpret this result as significant. There were only 8 subjects using titanium TORP, without statistical significance for both successful rate (67.6% in PORP vs 75.0% in TORP, P = .686) and post-ossiculo ABG (25.0 dB in PORP vs 20.2 dB in TORP, P = .157). In a study to identify the effectiveness of bone-cartilage composite graft (BCCG) as a material for ossiculoplasty also, titanium TORP showed more favorable hearing gain, 7.8 dB in PORP and 11.4 dB in TORP. ¹⁰ However, this study did not deal with the result meaningfully for the same reason as our study; there were only 9 cases using titanium in CWUM. In fact, at least in CWUM, the correct interpretation of this result was that whether PORP or TORP may not be a significant factor in the audiological outcome. This was also supported by the fact that “absence of stapes suprastructure (TORP)” was not identified as a significant variable in the multivariate analysis (Table 2). Accurate length and stable setting are important to maximize the hearing improvement from TORP. We used calipers and dummy sizers to accurately adapt the stapes footplate and reconstructed eardrum. Gelfoam and soft tissue were sometimes used to stabilize TORP standing. This trial demonstrated favorable outcomes of TORP.

There were some studies comparing Polycel® with titanium. Faramarzi et al ²⁰ investigated the efficacies of 2 materials; either Polycel® (n = 52) or titanium (n = 54) was randomly assigned in ossiculoplasty using PORP. Both groups decreased ABG by approximately 13 dB; there was no difference. Out of 106 subjects in this study, however, only 9 (8.5%) received CWDM as TM. The rest were 55 with tympanoplasty only and 42 with CWUM. Our study was different in that we did not include patients who underwent tympanoplasty and involved 140 subjects with CWDM. Faramarzi et al ⁸ also performed an investigation comparing these 2 materials in TORP; both materials showed no difference, with ABG improvement of about 11 to 12 dB. Meanwhile, there was a study comparing 2 materials in single-stage surgery, concurrently performed with TM. Titanium showed more favorable hearing outcomes, but it could not obtain the statistical significance in comparison with Polycel®. ⁹ In the aforementioned study using BCCG, the audiological outcomes of Polycel® and titanium were suggested. However, there also was a limitation to obtain significances in the comparison; Polycel® was implemented in 213 subjects, while titanium was only in 20. ¹⁰

Our study was deliberately designed to overcome the limitations of previous literatures. As a result, in CWUM, both Polycel® and titanium showed favorable outcomes, and the difference between the materials was not remarkable. However, in CWDM, titanium material was more advantageous in hearing improvement. Although there were no statistical differences in the success rates in the 2 groups, the improvement of hearing was more significant in the titanium group (Figure 3). In a recent study comparing various types of the graft, including titanium, the efficacy of titanium was not remarkable in CWUM, but were more pronounced in CWDM. ¹³ In particular, at low frequencies, CWDM is disadvantageous to CWUM, so the relatively poor outcome of the ossiculoplasty in CWDM is inevitable. ²⁸ Titanium can give a chance to retrieve this disadvantage of CWDM.

The titanium prosthesis kit has sizer dummies of each size; thus, the surgeon can determine the best length of the graft by inserting each dummy between the stapes and tympanic membrane. Meanwhile, the Polycel® kit does not have such sizer dummies. A previous study comparing titanium with autograft suggested that the use of dummy sizers in titanium prostheses can affect better surgical outcomes. ²⁹ However, we disagree that the sizer dummies are a major factor in determining the surgical outcome. When we used Polycel® as the graft, titanium sizers were often used to determine the optimal length for a patient. If necessary, after the measurement by the sizers, we cut Polycel® to fit the length.

A histological study using the gerbil middle ear showed that, after porous prostheses such as Plastipore®, Proplast®, or Polycel® were inserted, particulates decomposed gradually, and therefore, the biocompatibility might be reduced.^{30 -32} As CWDM may be more disadvantageous in maintaining the structure of the chain, the surgical outcomes of the Polycel® group in the study were worse in patients who underwent CWDM. In contrast, the decomposition has been reported less frequently in titanium. ³³ However, there is a problem that titanium has a high affinity for bone. Once a titanium prosthesis establishes a bone connection with the surrounding area, fixation with ossicle, especially in the stapedial head, can occur, which becomes troublesome when revision surgery is performed. ³³ For this reason, the authors used Polycel® when ossicular reconstruction was performed concurrently with TM.

Comprehensively, based on the present and previous studies to date,^{14 -18} titanium may be a more appropriate prosthesis for ossiculoplasty following TM, even in long-term follow-up studies.^34,35 In more detail, if CWDM is performed as TM surgery, it is better to consider the use of titanium. In patients who underwent CWUM, on the other hand, the graft material can be determined by the preference of a surgeon.

The status of the middle ear mucosa or the Eustachian tube function has been known to be a prognostic factor in the success of ossiculoplasty.^21,36 In this regard, we measured the middle ear space and attempted to identify whether the size of this cavity was related to the success of the surgery. In our study, narrow middle ear space was identified as a negative factor. It corresponds to the previous study showing the relationship between the middle ear space and hearing. ²⁸ The middle ear space estimated in the study, however, was not a real volume measurement through 3-dimensional reconstruction. Therefore, the authors thought that the effectiveness of graft materials for the narrow middle ear space could not be determined by this study.

Conclusions

In cases where CWDM was performed as the TM surgery, the effectiveness of titanium material was more pronounced than that of the Polycel® prosthesis. On the other hand, in CWUM, because both Polycel® and titanium showed favorable outcomes, surgeon may use a preferred material.