Biocompatible, conforming, and easy-to-use materials-these are the key characteristics of innovations in middle ear reconstruction, according to several experts.
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March 2007Whether the devices are titanium or shape-memory, or whether the prosthetics utilize autologous bone or soldering with laser, the quest is guided by these standards.
These developments are the culmination of years of incremental progress. In this report, ENToday briefly reviews some of the progress of the past decade and then points out recent advances that key opinion leaders consider to be critical.
Size of Prosthesis Influences Surgery Outcome
A hallmark study in 1995 had shown that the use of analytical models could predict the size of prostheses needed for optimal results after stapedectomy and tympanomastoid surgery.1 Noting the contribution of mechanical and acoustic models of the human middle ear to gauge the performance of various middle ear reconstructive procedures, the authors noted that model analyses could be used as the rationale for stapes prostheses of 0.6 to 0.8 mm in diameter in order to produce air-bone gaps of less than 12 dB and that, ironically, smaller-diameter prostheses produce larger air-bone gaps. These models also helped establish that the mass of a stapedectomy or ossicular replacement prosthesis could be 16 times greater than that of the stapes with little effect on the hearing result, and that the volume of the middle ear air spaces after tympanomastoid surgery should be at least 0.5 cc for optimal acoustic results. The models also helped establish the effectiveness of the round window graft in certain tympanoplasties as an important parameter determining the hearing result and helped show that the shield should be as rigid as possible to maximize postoperative hearing.
Autologous Incus and Diode Laser Soldering
A later retrospective study of tympanoplasty and ossicular chain reconstruction as a one-stage procedure involved the temporalis fascia for myringoplasty and a sculptured autologous incus to bridge the malleus to the stapes head and the malleus to the footplate.2 Of the 150 patients, 126 (84%) had a healed tympanic membrane three months postoperatively. One year later, 121 (81%) had an intact tympanic membrane, as did 119 (79%) five years later.
At this time, initial studies began to assess the potential use of diode laser soldering as a way to improve the mechanical stability of middle ear reconstruction.3 In that study, investigators evaluated the strength of soldered bonds by assessing the strength of soldered junctions that used fascia, cartilage, bone, and hydroxyapatite with a diode laser consisting of 810-nm wavelength and 50% albumin with 0.1% indocyanine green dye. By comparing the soldered bonds to those obtained with adhesive alone and by soldering 10 hydroxyapatite prostheses that were soldered to the stapes in human cadaver temporal bones, the investigators measured the force required to disrupt the bonds and found that the soldered bonds were significantly stronger.
Titanium and Shape-Memory Materials
Since then, the field has progressed to such innovations as titanium and shaped memory implants, and research on diode laser soldering has continued.
In separate interviews, leading experts discussed their own views regarding the innovations that are shaping the future of middle ear reconstruction.
The newest innovation is the use of stapes titanium implants, said Frank M. Warren, MD, Assistant Professor of Otolaryngology at the University of Utah. The hearing results are very good. Another advantage of titanium is that it is not ferromagnetic, and therefore not affected by a magnetic resonance imaging [MRI] magnet. Therefore, patients who have such implants could subsequently undergo an MRI scan without concern that the prosthesis would interfere with the scan. Titanium is also highly biocompatible and therefore associated with a lower extrusion rate than earlier materials used. It is also effective in closing air-bone gaps and is mechanically sounder and less top-heavy than other prostheses, he said.
Some bridge the gap between the malleus and stapes, and others between a necrosed incus and the stapes superstructure. These prostheses are geometrically complex to allow for the misalignment of the structures, and crimp in order to make the bridge possible.
However, Dr. Warren cautioned that the routine use of cartilage to cover the prosthesis and prevent extrusion is still necessary.
Paul R. Lambert, MD, Professor and Chair of Otolaryngology-Head and Neck Surgery at the Medical University of South Carolina in Charleston, agreed with Dr. Warren regarding the impact of titanium implants on the progress in middle ear reconstruction. He called it an ideal ear bone replacement medium for the middle ear, and elaborated on this statement.
The use of titanium implants is the most significant advance in ossicular reconstruction in the last 20 years, he said. Especially, those used as partial or total ossicular replacement prostheses have been important. In my years of otologic work, I’ve used a number of different materials. I began using titanium implants in 2003. I’ve only seen one extrusion in those years.
As did Dr. Warren, Dr. Lambert stressed the biocompatibility of titanium. Another advantage is the lightness of the material, he added. This property makes titanium implants very easy to position, he said. They’re very lightweight, very easy to position, and more secure. We see less displacement of prostheses. We also see better hearing results. Titanium has a hearing improvement of approximately 10 dB compared with other prostheses, he said.
One reason that otolaryngologists have had a strong interest in titanium middle ear implants is titanium’s proven track record as an implant in other anatomical areas. As I talk with my colleagues throughout the country, I think my experience mirrors theirs, Dr. Lambert added. I think most people are very pleased with the properties in titanium that we are seeing.
Titanium implants are also being used in stapes replacement prostheses, Dr. Lambert said. However, because such patients usually have excellent surgical outcomes, it would be difficult to see a statistically significant impact that titanium has in that setting, he said.
Regarding the overall field of titanium implants, Dr. Lambert emphasized that otolaryngologists should temper the positive results with caution. With any middle ear prosthesis, it is prudent to evaluate long-term data, and long-term data for middle ear work should include a minimum follow-up of three years, with a follow-up of five to 10 years ideal.
Other newer prostheses include those that are designed for revision stapes surgery, Dr. Warren said. These prostheses are designed with angles that accommodate incus necrosis, the most common need for revision.4
Other materials that otolaryngologists are using for ossicular reconstruction outside of the stapes include hydroxyapatite cements and bone cement, he said.
Innovative Surgical Approaches
In addition to diode laser soldering, some investigators are using an erbium:YAG laser to perform stapedotomy, Dr. Warren said. The advantage of using this laser is that the surgeon can set the laser spot to a specific diameter to create the opening, he said. You don’t have to touch or put anything into the middle ear because the laser puts a hole into the footplate at the size designated by the surgeon, he said.
Posterior footplate repositioning is another innovative surgical approach, he said. Since the otosclerosis is in the anterior footplate, some are doing what they can to preserve the posterior aspect, he said. In this setting, the footplate is deliberately fractured and the posterior aspect is used as an autologous prosthesis. The hope is that using autologous middle ear bones will produce for more natural hearing, Dr. Warren said.
We’re using fewer incus homografts, primarily because of the quality of prostheses, he said. There’s no one thing that everyone’s doing because there are a lot of ways to skin a cat. In otolaryngology, we have a lot of well-trained people who do it a lot of different ways. There are more choices today than there were 10 years ago. This plethora of choices may make the decision of which prosthetic materials and which procedures to use more complicated. The innovations even extend to packing materials, he added, noting that a new hyaluronic gel is clear and allows for visualization of the implant after packing the ear, and it also decreases scar tissue in the ear.
Glen Knox, MD, Clinical Associate Professor of Otolaryngology at the University of Florida in Gainesville, pointed out that innovative designs of prostheses are also influencing the field, such as the SMart™ Stapes prosthesis, which uses nitinol, a nickel-titanium alloy that has the advantage of shape-memory. These prosthetics are not only useful for stapes surgery. For example, if a patient has an absent incus and stapes, the otolaryngologist now can use the shape-memory malleus-to-footplate prosthesis, he said. It’s useful for patients with surgery for middle ear disease in which ossicular reconstruction is needed. They are also useful in patients who have had a cholesteatoma that has involved more than one ossicle and have had the stapes removed. People will do staged reconstruction if the malleus is present, and in such cases, you can use this material to reconstruct the middle ear.
Dr. Knox believes that materials that have shape-memory properties will be used more and more. I certainly think that such materials will continue to be used in middle ear surgery for the foreseeable future, he said. He noted that, because the material conforms to the shape of the incus or malleus without crimping, there are fewer critical steps a surgeon has to perform. Therefore, shape-memory materials are easier to use. Materials that can be used as bone replacement are also important, he said.
However, he stressed that the innovative materials have not yet caused autologous prostheses or older materials to become obsolete. We are still using autologous methods, Dr. Knox said. If the incus bone is present, a sculpted incus malleus-to-footplate prosthesis can be constructed. In addition, hydroxyapatite is still being used, and diode laser soldering may become increasingly important in the future. Dr. Knox noted that another trend to watch is the research being conducted with implantable and semi-implantable hearing aids with the transducer attached to the ossicles.
The shape-memory methods in middle ear reconstruction, along with the wide use of other prosthetics, as well as implantable and semi-implantable hearing devices, will shape middle ear surgery in the near future, Dr. Knox said. These are the trends that are advancing middle ear reconstruction.
Although the field abounds with innovation, surgeons should not feel pressured to try them all, he observed. The appropriate new modalities to use depend on the surgeon’s preferences and experience, he said.
Key Trends in Middle Ear Reconstruction
The experts interviewed for this report identified several key trends in materials and procedures that are advancing middle ear reconstruction. They are summarized below.
Materials
- Titanium: this biocompatible material, which has been used for several years for implants in several anatomical areas of the body, has also been identified as useful in middle ear reconstruction. Titanium implants are lightweight, easy for surgeons to position, nonreactive to ferromagnetism (and therefore do not complicate MRI), and stable, with a low incidence of extrusion. Companies manufacturing titanium implants include the German company Stryker Leibinger Co.
- Shape-memory: These fluoroplastic materials are characterized by their ability to soften in contact with body heat and conform to the individual’s middle ear structures. One example is the SMart™ Stapes, manufactured by Gyrus ENT (formerly Richards Medical Company).
- Hydroxyapatite: Although used in prostheses for several years, hydroxyapatite still has utility as a material for middle ear prostheses. Several companies manufacture hydroxyapatite middle ear prostheses.
- Autologous bone: Autologous bone, particularly the incus and the posterior aspect of the stapes, is often used in cases where the anterior component is absent.
Laser Procedures
- Diode laser: The diode laser is used to solder the implant to the anatomical junctions that it bridges. Diode laser soldering is still investigational.
- Carbon dioxide laser: The CO2 laser is used in middle ear surgery as a way to make a stapedotomy that is the precise size that the surgeon needs. It provides a hands-off way to perform stapedotomy with uniform results.
Other Intraoperative Materials
- Transparent hyaluronic gel: This material has the advantage of allowing visualization of the implant after the surgeon has packed the ear. It is manufactured by Genzyme under the name Sepragel.
References
- Rosowski JJ, Merchant SN. Mechanical and acoustic analysis of middle ear reconstruction. Am J Otol 1995;16(4):486-97.
- Khan I, Jan AM, Shahzad F. Middle ear reconstruction: a review of 150 cases. J Laryng Otol 2002;116(6):435-9.
- Ditkoff M et al. Potential use of diode laser soldering in middle ear reconstruction. Lasers Surg Med 2002;31(4):242-6.
- Gardner EK, Jackson CG, Kaylie DM. Results with titanium ossicular reconstruction prostheses. Laryngoscope 2004 Jan;114(1):65-70.
©2007 The Triological Society