Chapter 13 Ossicular Reconstruction
Reconstruction of the middle ear sound transformer mechanism has continued to evolve since the pioneering efforts of Wullstein and Zollner in the 1950s. Despite improvements in materials and refinements in surgical technique, complete closure of the air-bone gap on a consistent basis has proven elusive. The excellent hearing results consistently obtained with stapedectomy procedures are not as readily achieved when reconstructing the other middle ear ossicles. In addition, problems with extrusion may jeopardize early hearing gains. This chapter addresses some of the factors responsible for this disparity, and discusses techniques and materials that may assist the surgeon in optimizing the postoperative hearing results, while minimizing the likelihood of extrusion.
Since Matte’s1 report of a myringostapediopexy in 1901, numerous methods have been attempted to bridge the gap between the tympanic membrane and the inner ear fluids. The modern era of reconstructive middle ear surgery began with reports by Zollner in 19552 and Wullstein in 1956.3 These early attempts focused on creating a sound pressure differential between the oval and round window by adapting the operation to the ossicular problem encountered. If the incus was missing, the graft was placed on the stapes capitulum (type III or columellar tympanoplasty). If the incus and the stapes crura were missing, the graft was laid on the promontory, leaving a mobile footplate exposed (type IV, oval window, or cavum minor tympanoplasty), producing sound protection fort the round window. These techniques usually altered the volume of the middle ear by creating an open mastoid cavity. In 1957, Hall and Rytzner4 described the use of an autogenous incus or malleus to reconnect the mobilized footplate to the tympanic membrane in patients with otosclerosis. Hearing results with this technique were very promising, and the importance of a closed mastoid cavity with a normal middle ear space was quickly realized. Soon thereafter, the search for the ideal material to reconstruct the sound conduction mechanism was begun. In the late 1950s and early 1960s, much attention was focused on the use of autogenous and alloplastic materials.
The first reported use of an artificial material to reconstruct the ossicular chain was by Wullstein in 1952,3 when he used a vinyl-acryl plastic known as palavit to connect the tympanic membrane to the stapes footplate. In 1958, Shea5 described the use of polyethylene tubing placed on the capitulum of the stapes and wedged under the tympanic membrane. His efforts were soon followed by others using various polyethylene prostheses and other inert materials, such as polytef (Teflon) and silicone elastomer (Silastic). Despite many excellent short-term and long-term hearing results, these early alloplastic materials often resulted in extrusion, significant middle ear reactivity, or, worse, penetration of the inner ear. As a result, many surgeons turned to autogenous prostheses that would be more compatible with the middle ear.
Following the early work of Hall and Rytzner,4 several otologists, including Farrior,6 Sheehy,7 and Guilford,8 began reporting on the success of using autografts for ossicular reconstruction. The most commonly used autograft material was the body of the incus; however, cartilage and cortical bone were also used. These natural materials were well tolerated in the middle ear and provided reliable hearing results. The disadvantages that soon became apparent were the prolonged time required to sculpt the prosthesis and the lack of availability in chronically diseased ears. In an effort to circumvent some of these issues, in 1966, House and colleagues9 first reported the use of homografts in middle ear reconstruction. Other reports soon followed describing the use of irradiated ossicles, cartilage, and even homograft tympanic membranes with en bloc ossicles.10,11 Homografts had hearing results and biocompatibility similar to autografts; however, concerns regarding the risk of transmission of human immunodeficiency virus and prions (i.e., Creutzfeldt-Jakob disease) ultimately led to their decline in use.
In a continued effort to find a safe, reliable, and easily available prosthesis, Shea in 197612 reported on the use of high-density polyethylene sponge (Plastipore) for middle ear reconstruction. Made of porous polyethylene, this alloplast had nonreactive properties and sufficient porosity to allow ingrowth of tissue. It was readily available commercially and could be easily trimmed with a knife. A similar porous polyethylene that is thermal-fused (Polycel) was developed later and allowed the prosthesis to be coupled to other materials, such as stainless steel. This capability allowed it to be modified to various prosthesis designs. Early reports of porous polyethylene implants revealed a high incidence of extrusion when placed in direct contact with the tympanic membrane. This problem was significantly reduced by placing a disc of cartilage between the head of the prosthesis and the tympanic membrane, as advocated by Coyle Shea and reported by Brackmann and Sheehy.13 As a result, Plastipore and Polycel total ossicular replacement prostheses (TORPs) and partial ossicular replacement prostheses (PORPs) continue to be used with good long-term success today.
In an effort to improve extrusion rates associated with porous polyethylene, in 1979 various ceramics were recommended for use in ossicular reconstruction. These alloplastic materials were termed either bioinert or bioactive. Bioinert implants, such as dense aluminum oxide ceramic, did not react with surrounding tissues and were popular in Germany and Japan. Bioactive implants, such as glass ceramic (Ceravital), were biocompatible and reacted with surrounding soft tissue and adjacent bone allowing a coupling between the implant and the ossicle in contact.14 The advantage of ceramic implants was that they could be placed directly under the tympanic membrane without interposing cartilage; however, they were difficult to handle and shape because of their glass nature.
In 1984, Grote15 introduced the use of the calcium phosphate ceramic, hydroxyapatite, for tympanoplasty surgery. Subsequently, great interest developed in this material for middle ear prostheses. Hydroxyapatite, which is the mineral matrix of living bone, was known to be a bioactive material achieving integration with surrounding bone and tissue. In 1985, Wehrs16 developed an incus prosthesis and an incus/stapes prosthesis made of hydroxyapatite and reported successful hearing results with a low extrusion rate 4 years later. Since that time, this material has been adapted to various uses and prosthesis designs. The advantage of this material is that it is quite rigid and has a good sound transfer function.
The disadvantages of hydroxyapatite are that it has a large mass creating a high input impedance, and it is solid, potentially obstructing the surgeon’s view. Because of its brittleness, it is often combined with other materials to create a prosthesis shaft that is more malleable and easier to shape. More recently, hydroxyapatite has been combined with polyethylene (HAPEX) to create an allograft material that approaches the mechanical strength of bone, but is soft enough to cut with a knife.
In an attempt to find a prosthesis that had the rigidity and biocompatibility of hydroxyapatite, but not the mass, titanium prostheses were developed. The specific density of titanium is low, less than 57% that of stainless steel, yet it is extremely rigid. In addition, it is nonmagnetic, has excellent biocompatibility, and lends itself to being manufactured into various shapes and sizes. Most of the titanium prostheses possess an open head, allowing better visualization during placement. First used for ossicular reconstruction in 1993 in Germany,17 the popularity of titanium prostheses has grown rapidly. Cartilage must still be used, however, between the platform and tympanic membrane to prevent extrusion. Several authors to date have published favorable hearing results with titanium prostheses, and compared with hydroxyapatite, titanium may provide improved hearing responses at higher frequencies because of its low mass.18–21
Despite the improvements in middle ear prostheses, there remained a need for an adhesive or bone cement to stabilize the prostheses or, in some cases, replace them altogether. In the 1980s, ionomeric cements were used for cranioplasties and ossicular chain reconstruction. Although effective in the middle ear,22 aluminum toxicity issues associated with cranioplasties resulted in ionomeric cements being largely supplanted by hydroxyapatite phosphate cements, which are free of aluminum. Two of these cements currently are being produced for otologic applications—Hydroset (Stryker) and OtoMimix (Gyrus). The cements seem to be well tolerated, and have been particularly useful in reconstructing the long process of the incus and stabilizing prostheses.
Although numerous techniques and materials have been used for ossicular reconstruction, the quest for the ideal prosthesis is ongoing. Today, autogenous and alloplastic prostheses are used with equally good outcomes, and the surgeon should use what is comfortable and provides consistent, favorable results. This chapter primarily focuses on the use of alloplastic material in ossicular chain reconstruction, and principles that improve outcomes in attempts to reconstruct the middle ear sound transformer mechanism.
The selection of patients undergoing ossicular chain reconstruction largely depends on the problem at hand. Any patient with chronic otitis media may ultimately be a candidate for ossicular chain reconstruction. These patients often present because of the hearing loss associated with their infection or chronic middle ear disease. In other cases, initial hearing may be normal, but become compromised secondary to surgery to remove cholesteatoma. Still other patients present with hearing loss resulting from ossicular problems associated with trauma or congenital ear malformations. Regardless of the cause, the initial evaluation requires a thorough microscopic examination of the ear to identify the problem accurately.
In cases of chronic ear disease, ossicular discontinuity may be diagnosed through a perforation or with severe atelectasis of the tympanic membrane. Most commonly, incus erosion is the cause of conductive hearing loss; however, the presence or absence of all three ossicles should be noted. Cholesteatoma involvement of the ossicles is usually identified on examination. In the event of active infection and drainage, it is important to obtain a dry ear with meticulous cleaning and topical antimicrobial preparations before surgery. If a dry ear cannot be obtained, ossicular reconstruction is often staged after tympanoplasty so that ventilation and the middle ear mucosa can normalize. When there is a conductive hearing loss with an intact eardrum, the history should focus on any head or ear trauma, prior ear surgery, family history of otosclerosis, Tullio phenomenon, or unusual congenital abnormalities. Careful evaluation of the symptoms and findings guides the surgeon in the need for surgery, type of procedure, its urgency, and the anticipated result, based on the type of reconstruction required.
Audiometric studies are essential in patients with suspected conductive hearing loss and should include pure tone air and bone conduction with masking, speech discrimination, and tympanometry. Severe eustachian tube dysfunction may necessitate concomitant ventilation tube placement or, in rare cases, preclude ossicular chain reconstruction. Acoustic reflex testing is helpful in distinguishing hearing losses resulting from otosclerosis versus an inner ear conductive hearing loss associated with dehiscence of the superior semicircular canal. In the latter, the reflex is present. Conductive hearing losses greater than 25 dB usually signify an ossicular problem. Audiometric results should always be confirmed with the Weber and Rinne tuning fork examination using 512 Hz and 1024 Hz tuning forks. Before operating on the involved ear, the contralateral ear must be assessed. In cases of a better or only hearing ear, alternatives such as a hearing aid or a canal wall down procedure in the setting of chronic otitis media with cholesteatoma may be more suitable.
Imaging studies are rarely obtained to evaluate the middle ear and ossicles. Thin-section computed tomography (CT) of the temporal bone may provide useful information, however, in cases of extensive cholesteatoma, malleus fixation, incus dislocation, superior canal dehiscence, or suspected congenital ossicular abnormalities.
After a thorough work-up, the physician is prepared to give realistic expectations regarding the chance of hearing restoration and the need for additional surgery. Although ossicular reconstruction may be performed at the time of initial repair or cholesteatoma removal, extensive cases often require reconstruction to be done during a second stage at a later date. In adult patients, 9 to 12 months are allowed to pass before performing a second look procedure to rule out residual cholesteatoma and reconstruct the ossicular chain; in pediatric patients, 6 months is an appropriate time interval. This staging period provides adequate time for small residual cholesteatoma to become apparent, and provides time for diseased mucosa to normalize. Typically, absorbable gelatin film (Gelfilm) is placed over the promontory, and the middle ear is packed with middle ear packing soaked in Merogel a nonototoxic antibiotic solution. Enzymatic type packing in conjunction with the Gelfilm should decrease postoperative middle ear adhesions. Staging in this manner helps to ensure a disease-free ear, and improves hearing outcomes.
The selection of pediatric patients for ossicular reconstruction depends largely on the status of the ear. In the setting of chronic otitis media, the most important goal is to provide a safe, dry ear regardless of age. When a conductive hearing loss is discovered without evidence of chronic ear disease, it is best to wait until the child is 5 to 7 years old to allow time for eustachian tube maturation. If hearing loss is bilateral, hearing aids are a suitable option until that time. When surgery is contemplated, the options, including the use of hearing aids, must be discussed with the parents, who will ultimately make the decision.
When discussing outcomes with patients, it is important to provide a realistic expectation of hearing results. Successful hearing results in ossicular reconstruction are based on the postoperative air-bone gap and stratified as excellent (<10 dB), good (11 to 20 dB), and fair (21 to 30 dB). This success also depends on several factors including the presence or absence of a mobile stapes superstructure, intact canal wall with normal middle ear volume, and adequate eustachian tube function. Although outcomes vary slightly depending on the type of prosthesis used, successful improvement in hearing is generally broken down according to the use of a PORP versus a TORP. In patients undergoing ossicular reconstruction with a PORP, two thirds of patients should achieve hearing outcomes within 15 dB of their bone scores, whereas two thirds of patients with a TORP should achieve hearing outcomes within 25 dB of their bone scores. The disparity in outcomes between PORPs and TORPs is apparent in Brackmann and Sheehy’s review of 1042 cases in which successful hearing with an air-bone gap less than 15 dB was achieved in 63% of PORPs and only 42% of TORPs.23 Regardless of the technique or type of prosthesis, surgeons should use what they are most comfortable with and provides consistent good hearing results.