|Year : 2014 | Volume
| Issue : 4 | Page : 173-177
Cortical bone total ossicular replacement prosthesis
Manu Malhotra1, Saurabh Varshney1, Rashmi Malhotra2
1 Department of Otorhinolaryngology, All India Institute of Medical Sciences, Rishikesh, Uttarakhand, India
2 Department of Anatomy, All India Institute of Medical Sciences, Rishikesh, Uttarakhand, India
|Date of Web Publication||13-Dec-2014|
3/4, Type IV, All India Institute of Medical Sciences, Rishikesh 249 201, Uttarakhand
Source of Support: None, Conflict of Interest: None
Objectives: Evaluate an autologous cortical bone total ossicular replacement prosthesis (B TORP) made of cortical bone for cost effective and sustainable hearing results. Materials and Methods: A prospective study was undertaken in the patients who underwent tympanoplasty with new B-TORP from January 2011 to December 2011. All patients had an absent superstructure of the stapes and long process of the incus due to chronic otitis media. Totally 40 patients were evaluated. Hearing results were evaluated using four-frequency average pure tone air conduction and air-bone gap (ABG) measured at 0.5, 1, 2, and 3 kHz after a period of 12 months. Pre- and post-operative continuous variables were compared using a paired t-test and data from unequal groups were assessed for significant differences using unpaired t-test. Results: Successful rehabilitation of the ABG to 20 dB or less was achieved in 95% of patients. Overall mean improvement in ABG was 25.8 ± 5.6 dB, which was statistically significant (t = 26.8, P < 0.001). Mean postoperative ABG in the tympanoplasty only group was 12.9 ± 2.7 dB with an average improvement of 26.8 ± 4.9 dB (t = 22.0, P < 0.001) and in the intact canal wall group was 14.9 ± 5.1 dB with an average improvement of 24.5 ± 6.1 dB (t = 16.0, P < 0.001). There was no significant difference between ABG improvements of the two groups (t = 1.2, P > 0.5). Conclusion: The new autologous B-TORP provides sustainable hearing improvement and is bio-compatible, stable, and magnetic resonance imaging compatible.
Keywords: Autografts, Ossicular replacement prostheses, Otologic surgical procedures, Tympanoplasty
|How to cite this article:|
Malhotra M, Varshney S, Malhotra R. Cortical bone total ossicular replacement prosthesis. Indian J Otol 2014;20:173-7
| Introduction|| |
Ossicular chain damage is the common complication of chronic otitis media (COM), which forms the major bulk of the outdoor cases in Otolaryngology Departments, especially in developing countries. The reconstruction of the middle ear hearing mechanism damaged in the disease started in 1950s. The initial attempts aimed at varying the position of the tympanic membrane in order to alter the volume of the middle ear. This was followed by ossicular reconstruction using a homograft or allograft ossicles. Later varieties of plastic and ceramic materials were used. The ideal ossicular replacement material is yet to be established.  Titanium which was introduced by the American otolaryngologists in late 1990s, was actually used in a significant number of the patients in Germans in 1993. ,, Since then titanium has gained popularity due to its biocompatibility, improved handling suited to individual anatomy, improved signal transfer, and magnetic resonance imaging (MRI) compatibility.
In this study, we have tried to evaluate an autologous prosthesis made of cortical bone that is stable, provides useful hearing, is MRI compatible, and has negligible chances of extrusion. Data have been presented as per the guidelines of the American Academy of Otolaryngology-Head and Neck Surgery committee on hearing and equilibrium guidelines (AAO-HNS guidelines) for evaluation of the results of treatment of conductive hearing loss. 
| Materials and Methods|| |
A prospective study was undertaken in 40 patients from outpatient Department of Otolaryngology at a tertiary care center from January 2011 to December 2011. About 55% of the patients were having the mucosal variety of COM and 45% were having the squamous variety. All cases had an absent superstructure of the stapes, and the long process of the incus for which they underwent ossicular chain reconstruction using the new technique.
Patients with 15-60 years of age were included. The average age was 34 years. There were 29 males and 11 female patients. All these cases underwent routine ear-nose-throat check-up and necessary preoperative investigations. Audiograms assessing pure tone air (PTA) and bone conduction thresholds were obtained preoperatively. The cases having average bone conduction (at frequencies 0.5, 1, 2, and 3 kHz in the pure tone audiogram) above 20 dB, canal atresia, extensive cholesteatoma, fixed foot plate, extensive adhesions and required canal wall down mastoid surgery were excluded from the cohort to maintain the homogeneity of the results. In six cases, where the condition of middle ear mucosa was not healthy, ossicular replacement was done at the second stage surgery. If multiple audiograms were done preoperatively the last audiogram before surgery was used for the study. Twenty-two cases (55%) underwent tympanoplasty only, and 18 cases (45%) underwent intact canal wall (ICW) tympanoplasty [Table 1].
[Figure 1] demonstrates cortical bone autologous replacement prostheses bone total ossicular replacement prosthesis (B-TORP) construction. A block of cortical bone was taken from the mastoid. If adequate sized graft was not available from the mastoid, it was taken from the shin (tibia). The block was then carved into the shape like an umbrella using a 0.5 mm cutting and polishing burrs. Thickness of the vault was 1-1.5 mm to minimize bulk and the circumference was kept about 1-2 mm short of the bony annulus to allow movements. The stalk or the handle was carved out in a manner that the lower end of the stalk was shaped slightly broader (diameter of approximately 2 mm) and was flat on its base so that it rested stably on the stapes footplate. The height of the prosthesis was equal to the distance between the annulus and the footplate. The mean height of the B-TORP was 5 ± 0.9 mm (range: 3.5-7 mm). [Figure 2] demonstrates systematic approach of placement by two-point stabilization technique.  the reconstruction prosthesis. From an incision above the auricle, loose areolar tissue is harvested. It is pressed in a fascia press and allowed to dry. The footplate is closely inspected to verify mobility. The mucoperiostium around footplate is abraded with a small hook to encourage adherence to the areolar tissue graft. The graft is trimmed to a diameter of approximately 3-4 mm, so that it will cover the footplate and overlap slightly over the facial ridge and the promontory. The areolar tissue graft is slightly rehydrated and placed using cup forceps, then dimpled with 24 suction in order to receive the lower end of B-TORP. Next, the B-TORP is placed over the areolar tissue graft and oriented in a perpendicular fashion. This is done using a micro-cup forceps and a curved needle. The areolar tissue helps self-center the B-TORP and prevents direct contact between the prosthesis the facial canal, footplate and promontory. After placement over the footplate of the stapes, round window reflex is checked. The prosthesis is stabilized in such a manner that the contact between posterior middle ear wall is avoided. The graft was given a support of gel foam in situ and was covered with a temporalis fascia graft and finally the tympanometal flap is returned.
|Figure 1: Shaping the block of bone into bone-total ossicular replacement prosthesis|
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|Figure 2: (a and b) Missing suprastructure of stapes with mobile footplate of stapes; (c and d) areolar tissue graft placed over footplate; (e and f) placement and lateral stabilization of bone-total ossicular replacement prosthesis|
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Audiograms were taken at an interval 6 and 12 months postoperatively. Hearing results were evaluated using a four-frequency average PTA conduction and air-bone gap (ABG) measured at 0.5, 1, 2, and 3 kHz. The postoperative means were compared with those of preoperative audiograms. Hearing loss or gain was calculated from the difference between pre- and post-operative ABG and PTA.
All data were analyzed using IBM SPSS Statistics software version 20 (Statistical Product and Service Solutions). Continuous data were initially assessed for normality and expressed as mean ± standard deviation. Categorical data were expressed as count and proportions. Pre- and post-operative comparison of continuous variables was done using paired t-test and data from two separate and unequal groups was assessed for significant difference using an unpaired t-test. A two sided P = 0.05 was considered as statistically significant.
| Results|| |
Hearing results of all patients are summarized in [Table 2]. The mean postoperative ABG was 13.8 ± 4.0 dB showing the improvement of 25.8 ± 5.6 dB over the mean preoperative ABG of 39.6 ± 4.5 dB. The improvement in ABG was statistically significant (t = 26.8, P < 0.001). The mean postoperative PTA was 28.3 ± 6.6 dB showing the improvement of 26 ± 5.8 dB over the mean preoperative PTA of 54.3 ± 4.5 dB. The improvement was again significant (t = 20.6, P < 0.001). [Table 3] and [Figure 3] show that the closure of ABG within 10 dB or less was achieved in 25% of patients, within 20 dB or less was seen in 95% of the patients. The AAO-HNS guidelines define a mean postoperative ABG of 20 dB or less as a successful hearing result.  In terms of PTA, the successful rehabilitation to 30 dB or less was achieved in 75% and 35 dB or less in 95% of the patients [Table 4].
All the 22 patients (55%) having mucosal variety of COM and underwent tympanoplasty only with B-TORP had a successful restoration of hearing to postoperative ABG of 20 dB or less [Table 5]. In the other group where the 18 patients (45%) having a squamous variety of COM underwent ICW with B-TORP, 20 dB or less ABG was achieved in 88.9% of the patients. Postoperative PTA of 30 dB or less was achieved in 81.8% of patients with B-TORP only group and 66.7% of the patients in the ICW group [Table 6]. The mean postoperative PTA in B-TORP only group was 26.4 ± 4.5 dB showing an improvement of 27.2 ± 5.2 dB (t = 19.9, P < 0.001), and in ICW group was 30.6 ± 7.9 dB showing an improvement of 24.7 ± 6.3 dB (t = 11.4, P < 0.001). The mean postoperative ABG in B-TORP only group was 12.9 ± 2.7 dB showing an improvement of 26.8 ± 4.9 dB (t = 22.0, P < 0.001), and in ICW group was 14.9 ± 5.1 showing an improvement of 24.5 ± 6.1 dB (t = 16.0, P < 0.001). The details are shown in [Table 7] and [Figure 4]. The improvements in both groups were statistically significant. However, there was no significant difference between the two groups (t = 1.2, P > 0.5).
[Table 8] summarizes overall results hearing results with the type of procedure done. Only one revision surgery and no planned second stage surgery was done in the B-TORP only group. In the ICW group, two cases were taken for revision surgery and six cases were taken up for planned second stage surgery after 3-6 months. Second stage surgery was planned to rule out the possibility of recurrence or residual disease in patients having a squamous variant of the disease.
| Discussion|| |
The challenge in ossicular reconstruction is well-recognized. The last several decades have seen a shift from the autologous ossicles use to synthetic prosthetics.  Factors that can influence the acoustic performance of an ossicular prosthesis include its stiffness, mass, position, the tension and coupling. In general, the stiffness of an ideal prosthesis should be much greater than that of the stapes-cochlear impedance. For clinical purposes, prosthesis made of ossicles, cortical bone and most synthetic materials generally meet this requirement.  The literature shows enough evidence that autologous cortical bone grafts are good for ossicular chain reconstruction. ,,, Mills suggested that cortical bone is a satisfactory material for ossiculoplasty.  In 2009, Ceccato et al. described a technique of sculpting and shaping the ossicles, while still attached to the cortical bone.  They do not incite formation of new bone and do not undergo resorption. Like autologous ossicles, they undergo slow replacement of nonviable bone by new bone formation. ,,,
The last decade has brought titanium to the forefront. Numerous articles cite its advantages: Tissue compatibility, durability, rigidness, lightweight features and excellent acoustic capability. Titanium implants are also MRI compatible. The cost of implant, however, becomes an important issue in the developing nations, especially when the cost of the second stage surgery adds to it. Several authors have reported mean postoperative ABG ranging from 13 dB to 26 dB and closure of ABG to 20 dB or less in 40-66% of patients with titanium TORPS. ,,,,,,,,,, The current study reports mean postoperative ABG of 13.8 ± 4 dB and closure of ABG to 20 dB or less in 95% of the patients.
An autologous TORP called an "Umbrella Graft" was earlier introduced by Malhotra as a cost-effective alternative to titanium prosthesis.  This technique used the malleus for the stalk of umbrella whose vault was constructed with the conchal cartilage. The literature, however, recommends preservation of the malleus for optimum hearing results. ,,,, The natural angulations of the stalk of the malleus in the prosthesis would be yet another destabilizing factor.
The focus of this study is to develop and evaluate autologous cortical bone prosthesis as a cost-effective alternative to other popular synthetic prosthetics. The described B-TORP has better chances of integration with the stapes footplate, the two-point stabilization technique provides long-term stability, it is bio-compatible, adequately rigid for sound transmission, less bulky (as most of the bulk is drilled out) and is MRI compatible. The described prosthesis possesses most of the advantages of titanium prosthesis, it is cost-effective and above all shows promising postoperative hearing results.
The drawback of this study is that it does not include a randomized trial of B-TORP and titanium TORP. Strict case selection with exclusion of extensive cholesteatoma, sensorineural hearing loss, stapes fixation, canal atresia, and taking up doubtful cases of cholesteatoma for the second stage surgery can also be some of the reasons for good postoperative results.
| Conclusion|| |
The new cortical bone prosthesis provides cost-effective hearing results in patients requiring ossicular chain repair. A long-term prospective randomized trial comparing B-TORP and other synthetic prosthesis is however required to prove the efficacy of the same.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4]
[Table 1], [Table 2], [Table 3], [Table 4], [Table 5], [Table 6], [Table 7], [Table 8]