HISTORY OF OSSICULOPLASTY
The first recorded ossiculoplasty procedure was performed by Matte in 1901 for a missing ossicle in the form of myringostapediopexy. Since then numerous materials have been used to reconstruct the sound conducting mechanism in different situations. Various materials including both biological and alloplastic materials have been used in the last few decades.
Of all these materials, not many stood the test of time. The list of the materials used over the years by different surgeons is depicted in table 1 (those highlighted in bold are the ones which are still in use).
In 1952, Wullstein attempted to use an allograft in the form of vinyl acryl plastic as prosthesis between the tympanic membrane and stapes footplate. This attempt failed due to rejection of the implant. Other alloplastic materials tried were polyethylene (Shea), polytetrafluoroethylene (Austin), and metal (Palva). However, the results were so disappointing that the use of alloplastic materials was discontinued for a long time.
Hall and Rytzner (1957) performed the first ossicular reconstruction using an autologous incus, which was reshaped to fit between the manubrium of the malleus and the stapes head/footplate. Over the time, this has proved to be the most commonly used autograft material with postoperative air-bone gap closest to the normal. Other than incus, autologous malleus was also interposed between neo tympanic membrane and stapes footplate.
As autologous ossicles were not always available, Farrior (in 1960s) introduced autologous cortical bone and it is still being used at various centers with good results.
All these bone grafts (autologous ossicles and cortical bone) are dead bones which undergo new bone formation and remodeling by a process of “creeping substitution”. They could, therefore, maintain their morphological structure over the years. The chances of rejection are few; as the morphological structure is the same as that of the original bone, however, fibrous or osseous ankylosis can develop between the bone graft and surrounding bony structures like the facial canal or promontory causing recurrent conductive hearing loss.
In 1960–63, Utech and Jansen started using autologous cartilage as an alternative to ossicles and cortical bone. Cartilage did not fix to surrounding bone and was considered as an option to be used as a columella graft from tympanic membrane to footplate, but its lack of stiffness would be a significant disadvantage in physiologically transferring sound from the drum to the vestibule. Besides, its long-term stability is considered doubtful as cartilage does not contain vessels and depends on nutrition by diffusion and tends to get necrosed over time.
Autologous grafts have shown promising results all these years considering that these grafts become part of the host environment. Fusion of the bone graft to the malleus and stapes or footplate usually achieves an assembly closest to the normal woniteh good sound transmission.
However, for optimal results, these grafts should be of adequate length and width to avoid displacement at the stapes head/footplate.
In 1966, House came up with the idea of using homologous incus for the first time. It could be stored and prepared in specially created conditions for use in patients. The first ever transplant consisted of body and short process of the homologous incus. It was repositioned between the stapes head and the manubrium of the malleus. The risk of rejection and transmission of infectious diseases from donor to recipient led to its reduced usage/decline, though few prestigious centers all over world are still using it with no such limitations of either rejection or transmission of disease from donor to recipient.
The 1970s saw scientists all over the world developing newer alloplastic prosthesis so as to overcome the deficiencies of the autograft, homograft, and plastic implants of the 1950s and 60s.
It started with Proplast, a combination of two polymers, which could be utilized for middle ear reconstruction. A high percentage of Proplast’s volume is porous to allow for tissue integration and to prevent host graft rejection. These pores in the Proplast also allowed host fluids to infiltrate the prosthesis and facilitate the acceptance of the prosthesis. The unique problem with this prosthesis was its Teflon shaft, which was not amenable to contouring. A Teflon polymer, Proplast, had all the disadvantages of Teflon, particularly substantial reactivity in the middle ear.
In 1976, as an alternative to Proplast, Plastipore, a semisoft white sponge of high density polyethylene, was launched commercially all over the world as an alloplastic material and it is still being used. Being both rigid and easily sculpted due to its spongy nature, it became an excellent alternative to autograft and homograft ossicles. To reduce the risk of extrusion, a cartilage piece can be used as interface between the tympanic membrane and the head of the prosthesis. In spite of all the advantages of Plastipore, it was understood that the fibrous unions which take place between the shaft and the footplate could also occur between the shaft and the promontory, fallopian canal, and scutum leading to its failure. Despite some of its limitations, Plastipore is still favored by many otologists.
Aluminum oxide ceramic (Jahnke and Plester) in 1979 and Ceravital (Reck) in 1983 were other alloplastic materials which were tried but could not stand the test of time and were withdrawn from the market.
Hydroxyapatite made its debut in the early 1980s used for the first time by Grote. Hydroxyapatite is composed of calcium triphosphate (used in a dense or porous state) which is a bioactive ceramic that resembles the mineral matrix of bone, and in its dense state bonds to bone. As this material is considered biocompatible, the head of the prosthesis can be placed directly under the tympanic membrane without any cartilage graft in between. After hydroxyapatite’s introduction to middle ear surgery, there was a corresponding decrease in the use of Plastipore and homograft bone. To overcome the rigid and brittle nature of this material, various composite hydroxyl apatite prostheses have been developed like hydroxyapatite head plate with shaft made from other materials. These materials can be Plastipore, polytetrafluoroethylene, flex hydroxyapatite (hydroxyl apatite), and hydroxyl apatite reinforced polyethylene composite. These materials make the shaft easily trimmable. Success rate varies with each combination making it difficult to compare the results.
Although titanium was first introduced by the otolaryngologists in United States in 1990s. European otologists were the first to use titanium middle ear implants with very good results in mid-1990s. The material is light and strong, the weight being equivalent to the original ossicle and the current designs have an open head plate with improved visibility of the position of the lower end of prosthesis on stapes supra head/footplate. New designs of titanium partial ossicular replacement prosthesis (PORP), total ossicular replacement prosthesis (TORP), and angular prosthesis are being developed all the time making titanium prosthesis the most suitable of all the prosthesis designed till date.
There has not been much change in the materials used for autografts and homografts. However, if we look into development of different allografts, there has been tremendous advancement over the years. Till date, designs of TORPs and PORPs have focused on ease and speed of customization during surgery. Though there are other areas where the scope of improvement exists, such as research on how to correlate the acoustic response of the ossicular chain with the shape of the prosthesis. Currently, the only acoustical correlation with PORP or TORP is the weight of prosthesis being closest to the original ear bones, since this is of vital importance for a prosthesis to function properly. The creation of prostheses that are both easily customizable and replicate the behavior of the original ossicular assembly represents one of the biggest challenges for the biomaterial scientists and surgeons in developing newer ossicular prosthesis.
MATERIALS USED AT PRESENT
The materials that have sustained over the years in spite of newer interventions are discussed below.
Autograft (Tissue Harvested from the Patient’s Own Body)
- Head of malleus
- Floor, tragal, and conchal cartilage
- Cortical bone, external canal wall bone, and spine of Henle.
Homografts/Allogenic Grafts (Derived from Human Donor Tissue, Screened and Treated to Avoid Transmission of Disease and Preserved for Later Use)
- Incus, malleus, and stapes
- Septal cartilage.
Allografts (Synthetic, Biocompatible Implants that Can Be Safely Used in Middle Ear)
The most common allografts used over the years which have stood the test of time are:
- Hydroxyl apatite
All three varieties of ossiculoplasty grafts have their own advantages and limitations as well. These posed different challenges over the years, which led to the quest for newer biocompatible materials.
MATERIALS FOR OSSICULOPLASTY
The ideal prosthesis for ossicular reconstruction should be biocompatible, stable, and safe. It should facilitate easy insertion and yield optimal sound transmission. The weight of the prosthesis is equally important. Studies have shown that a weight of more than 5 mg can affect sound transmission above 1 kHz, so prosthesis should weigh less than 5 mg. The ideal situation is that the implant/prosthesis should not come into contact with the surrounding tissues other than the ones at its two ends.
The material of prosthesis alone cannot ensure good results. A surgeon chooses a particular prosthesis considering status of the ossicular remnants, chronicity of disease, and availability and affordability of specific material among others.
Our first choice has always been autologous incus or malleus head. If a usable autograft is not available, allografts, of which there are many, are used. We have also used homologous ossicles with necessary precautions and preservation techniques.
Preference of specific materials (based on results of ossiculoplasty, availability, and affordability of different materials) have been dealt with in this chapter explaining their advantages and disadvantages.
USABLE AUTOGRAFT INCUS
If the incus (Figure 1) is in a usable condition even after partial necrosis, it is the preferred material. It is known to give stable results when used as interposition graft, between the handle of malleus and stapes head/footplate. The affected long process of incus, which is the commonest site of necrosis, is drilled away and the remnant is sculpted as required.
FIGURE 1: A, Autograft incus remodeled into different shapes. B, Incus when placed between stapes and handle of malleus. C, Incus when placed between footplate and handle of malleus.
- Biocompatibility is the same, so there is no possibility of rejection
- Ideal consistency
- No added cost
- No risk of transmitting disease
- Can be done in single stage.
- Needs sculpting which requires good surgical acumen
- May harbor microscopic cholesteatoma, hence must be examined under microscope after its removal, for any epithelial invasion
- There is possibility of displacement of incus in case it is not interposed correctly, between stapes/footplate, and malleus
- Adhesions and/or bony ankylosis may develop between grafted incus and surrounding bone leading to failure of ossiculoplasty.
INCUS IS NECROSED AND/UNUSABLE
In case the patient’s incus is completely necrosed or found unusable due to micro or macroscopic invasion of cholesteatoma or granulations, other materials may be used. Although homologous incus was commonly used earlier, however, with the availability of allografts, there has been a sharp decline in it is use.
FIGURE 2: A, Head of malleus to be remodeled. B, Drilling a groove into head of malleus. C, Groove in head of malleus for stapes head.
Autologous Head of Malleus over Head of Stapes
The head of malleus (Figure 2) is a good choice in case suprastructure of stapes is present. It is used as columella graft and not as an interposition graft. It has the same advantages and disadvantages as the autologous incus.
Autologous Cartilage Graft
Cartilage can be harvested from any of the three sites; namely, tragal/chonchal/floor cartilage and trimmed into a cartilage strip with perichondrium at least on one side (Figure 3A). In case suprastructure of stapes is present, this straight strip is placed over head of stapes on one side and in a groove drilled in tympanic bony sulcus on the other side (Figure 3A). In case only footplate is present, it is converted into an L/boomerang-shaped graft by giving partial thickness cut along the horizontal axis towards one end of cartilage strip and placed between the footplate and the tympanic bony sulcus drilled in the anteroinferior quadrant (Figures 3B and C). It should be ascertain that the cartilage is strong and stiff enough to replace bony ossicles.
- Biocompatible—no possibility of rejection
- No added costs
- No risk of residual disease as graft is harvested from a site away from the disease
- No risk of transmission of disease as it is autologous in nature
- Single stage surgery.
- Different consistency than bone, so strength is not as good as that of bone
- There are chances of resorption over the years. Therefore, we must make sure that the graft is stiff and strong enough to stay there in place for a long time
- At the same time while sculpting the cartilage into a strip, the perichondrium is left intact on one side for better vascularity of graft
- Every case requires a different size of the cartilage graft depending on the dimensions of external auditory canal and middle ear. So the remodelling and reshaping of cartilage depends on the requirement of each case
- Both ends of the graft have to be properly fitting over the footplate and bony sulcus. There has to be enough space between the graft and medial wall of middle ear for optimal height and ventilation of middle ear.
Titanium Partial Ossicular Replacement Prosthesis/Total Ossicular Replacement Prosthesis/Angular Prosthesis/Piston
Since the introduction of titanium PORP/TORP in 1993, their use for ossiculoplasty has gained acceptance and popularity. In 1993, Dalchow designed the TORP (Arial) and the Partial (Bell) prosthesis. The design was enhanced when a new prosthesis that could be trimmed intraoperatively to the appropriate length was introduced by Spiggle and Theis in 1996 (Figure 4). It has the rigidity and biocompatibility of hydroxyapatite but not the mass. Kurz angular prostheses (Figure 5) made completely of titanium, gold, gold shaft, or gold cup only have also been developed and improved upon with time.
Studies have shown that within 28 days after implantation, a thin noninflammable, even layer of epithelium forms over the inserted implant. Titanium forms a biostable titanium oxide layer when combined with oxygen.
FIGURE 4: A, Titanium partial ossicular replacement prosthesis. B, Titanium total ossicular replacement prosthesis.
The properties of titanium make it possible to manufacture an extremely fine and light prosthesis with substantial rigidity in the shaft. Different processing techniques of the material surface triggers different tissue reactions. If titanium implants are rough milled, their contact points are increased in proportion to areas that come in contact with cartilage graft, stapes head, or footplate. Conversely, the smoother the surface, the less connective tissue reaction occurs, and the epithelial covering is minimized. Titanium pistons which can be simple clip piston or malleovestibulopexy pistons are much more advanced and easy to use than the preexisting Teflon piston (Figure 6).
- Most biocompatible alloplastic material available at present. It has low specific density, i.e., less than 57% of stainless steel which makes it extremely rigid, nonmagnetic, with excellent biocompatibility
- Most prostheses come with an open head hence, offer visibility during placement
- Is extremely light and fine and yet strong in the shaft
- Does not need any sculpting
- No risk of residual disease
- No risk of transmitting disease
- Results comparable to autologous incus.
- There is some possibility of formation of adhesions between the implant and surrounding tissue leading to failure of ossiculopolasty
- It is equally time consuming to trim length of shaft according to height of middle ear in every case. For the two point stabilization technique, a cartilage shoe has to be designed for supporting the small sized stud at the lower end of prosthesis on the bigger elliptically shaped footplate and right size of partial thickness cartilage graft has to be sculpted to be placed between prosthesis and tympanic membrane
- Though regarded as biocompatible, it can get extruded if it comes in direct contact with the tympanic membrane. So a partial thickness cartilage graft with perichondrium on one side has to be placed between the prosthesis and tympanic membrane.
Universal Titanium Prosthesis with Flex Hydroxyl Apatite Shaft and Titanium Shoe
This composite prosthesis (Figures 7 and 8) has the advantage, that we can use it as PORP, when titanium head and shoe are used together and it can be used as TORP if we cut the titanium shoe and use the flex hydroxyl apatite shaft instead.
FIGURE 7: Universal titanium prosthesis with titanium head and shaft which fits into flex hydroxyl apatite shaft with titanium shoe.
FIGURE 8: A, Hydroxyl apatite shaft with titanium shoe. B, Titanium head with shaft which can be trimmed according to the size required.
Hydroxyl Apatite Partial Ossicular Replacement Prosthesis/Total Ossicular Replacement Prosthesis
Grote introduced this polycrystalline calcium phosphate ceramic (Figure 9), which has the same chemical composition as bone. Being bioactive, it integrates with surrounding bone and tissues. Within two weeks of implantation, a large proportion of hydroxyl apatite implants get covered with an epithelial layer. With passage of time, the implant gradually gets completely covered with epithelial layer. The fine epithelial layer contains all the characteristic of the cells of the mucosa of middle ear. This is a good indicator of an excellent biocompatibility of an implant material.
- No risk of residual disease
- No risk of transmitting disease
- Results comparable to autologous incus
- More stable as it is rigid in consistency and performs good sound transfer function
- As this is a bioinert compound, the makers claim that partial thickness cartilage graft need not be kept between head of prosthesis and neo tympanic membrane. This does not hold true for Plastipore prostheses though. We still keep the cartilage piece in any case.
FIGURE 9: A, Hydroxyl apatite partial ossicular replacement prosthesis. B, Hydroxyl apatite total ossicular replacement prosthesis.
- There is some possibility of formation of adhesions between the implant and surrounding tissue leading to failure of ossiculopolasty
- It is equally time consuming as the length of shaft needs trimming according to height of middle ear in every case. For the two point stabilization technique, cartilage shoe has to be designed for supporting the lower end of prosthesis on the bigger elliptically shaped footplate and right size of partial thickness cartilage graft to fit between prosthesis and tympanic membrane
- Though regarded as biocompatible, it can extrude if it comes in direct contact with the tympanic membrane. So a partial thickness cartilage graft with perichondrium on one side has to be placed between the prosthesis and tympanic membrane
- Large mass which creates a high input impedance
- As the head of prosthesis is solid it can obstruct the surgeon’s view to the placement of lower end of prosthesis on stapes/footplate.
The disadvantage which limits use of hydroxyl apatite prosthesis to a large extent is that its size cannot be customized/trimmed as required because it is too brittle and the shaft breaks when pressure of any kind is applied. As explained earlier, to overcome this hurdle, it is often combined with other materials to create a shaft that is trimmable and easier to shape.
Plastipore Partial Ossicular Replacement Prosthesis/Total Ossicular Replacement Prosthesis
Plastipore has been the first alloplastic material commercialized and used worldwide (Figures 10 and 11).
FIGURE 10: A, Plastipore total ossicular replacement prosthesis trimmable yet rigid. B, Shaft can be cut to the desired size.
It is a semisoft white sponge of high density polyethylene. It has nonreactive properties with sufficient porosity to allow ingrowth of tissues. It can be easily trimmed with a knife. Short-term results were encouraging but it had unacceptable long-term extrusion rate (15–30%). Hence, a cartilage piece is used between prosthesis and tympanic membrane, which has reduced the extrusion rate to below 10%.
Teflon Partial Ossicular Replacement Prosthesis/Total Ossicular Replacement Prosthesis
Teflon is a biocompatible alloplastic material (Figure 12), however its use has substantially reduced after titanium PORP/TORP came into existence.
- Does not need any sculpting. Only the length needs trimming.
- No risk of residual disease
- No risk of transmitting disease
- Although proven to be biocompatible, there are fair chances of extrusion if it comes in direct contact with tympanic membrane. Therefore, in every case, we must use partial thickness cartilage graft with perichondrium on one side, between the prosthesis and newly constructed tympanic membrane
- Few cases have shown formation of adhesions between the implant and surrounding mucosa leading to failure of ossiculopolasty
- It is equally time consuming as the length of shaft needs trimming according to height of middle ear in every case. Cartilage shoe is to be designed for supporting the small sized lower end of prosthesis on the bigger, elliptically shaped footplate and finally the right size of partial thickness cartilage graft which sits between prosthesis and tympanic membrane
- Not as fine and light as titanium prosthesis
- Results are not as good as a titanium piston.
Homologous incus has been in use since 1966 and is used very cautiously. As there is a possibility, though quite low, of transmitting some diseases from donor to recipient, we must make sure that the donor is not suffering from any transmittable disease. Incus after removal from the donor site is to be properly prepared for usage in the recipient patient. It is first examined thoroughly under the microscope for any microinvasion after harvesting. Then the incus is thoroughly washed with saline and kept in 4% formaldehyde for 48 hours for fixation and then kept in 70% ethanol for minimum of 2 months before usage. At our center, we reserve their use in revision cases.
- Biocompatibility, contour, size, shape, and consistency are the same as that of original ossicle, so no chance of rejection or extrusion
- Cost effective
- Can be done in single stage.
- A very low possibility of transmitting disease from donor to recipient
- A very low possibility of rejection, if the graft is not prepared properly
- Needs remodeling and reshaping so requires good surgical acumen
- There is possibility of the incus harboring microscopic cholesteatoma. Therefore, we must examine incus under microscope after its removal to detect any such invasion. It should be used only when found free of disease
- In cases of absent suprastructure of stapes, the size of footplate should match the width of short process of incus for proper fit and stable assembly.
Three important points should be kept in mind. These are:
- Always make sure that the donor is not suffering from any transmittable diseases
- Perform all the steps to prepare the graft religiously in all cases
- Always inform the patient regarding usage of homologus grafts
Bone cement is the latest addition as an ossiculoplasty material in cases of incudostapedial joint necrosis with the gap between stapes head and incus less than 3 mm and minimal necrosis of long process of incus. Termed as incudostapedial rebridging ossiculoplasty with ionomeric/hydroxyapatite bone cement, it is a relatively newer and reliable technique for ossicular reconstruction that is cost effective and offers satisfactory hearing results in selected patients.
Bone cements are substances that have been used in dentistry as filling material. The formulated powder mixed with the dissolving liquid results in a mixture that hardens within minutes through an exothermic reaction.
The glass ionomer bone cement contains a powder composed of glass powder, polycarboxylic acid, and pigments, as well as a liquid composed of water, tartaric acid, and conservation agents. After mixing the two components, the material hardens to a bone-like consistency in 5–10 minutes. The cement can be shaped within a few minutes before hardening. The cement bonds directly with bone, and once the cement has set, it is no longer sensitive to surrounding fluids. These features make this material potentially useful in ossiculoplasty procedures.
Preparation of Bone Cement
Included in the sterile package of Ketac Cem Radiopaque are a powder and a dissolving liquid. The powder and liquid are mixed on a metal plate, causing a minimal exothermic reaction. The mixture becomes a paste before it is hardened in a couple of minutes, rebridging has to be performed within this period of time. With use of a dropper, the cement is deposited on the necrosed incudostapedial joint or the ossicular gap between the incus and stapes head. This material hardens at this stage and becomes a part of joint itself.
Selection of Patients
The distance between the remnant of necrotic incus and the stapes head is the most important criterion for selecting patients for use of bone cement. It can be either partial incudostapedial or complete necrosis of joint but the gap has to be minimal.
It is also proposed to be used:
- To stabilize the bony ossicles in their normal position
- In cases of necrosis of long process of incus in stapedotomy or in stapedectomy cases
- To secure ossiculoplasty prostheses like TORP or PORP in place
- In incus subluxations
- To fix the cartilage graft used to reconstruct the outer ear canal
- Fixation of cochlear implant array into the cochleostomy
- Fixation of hearing devices
- In cases of revision stapedotomy to secure the loop of the stapes over the incus.
Tympanic membrane grafting is performed after cement sets. Bone cement does not interfere with graft take up. Gel foam/piece of cartilage or perichondrium is placed between cement bridge and eardrum during grafting.
- It should be performed within minutes before the mixture becomes hard
- Any hemorrhage should be controlled before application of bone cement because it may interfere with hardening of the cement
- Mucosal covering over ossicles should be removed and bone cement should be applied directly over denuded bone since bone cement does not adhere to soft tissue
- Ionomeric bone cement should not come into contact with neural structures, perilymph, or dura because of its potential aluminum toxicity. Therefore, we always keep small pieces of gel foam over facial nerve, chorda tympani, and stapes footplate during application
- In case of contamination, immediate aspiration of cement and multiple irrigations and aspirations with serum are necessary to remove the cement. To prevent contamination, bone cement should be applied in its most suitable consistency. There have been no reported cases of toxicity secondary to glass ionomer cement ossiculoplasty.
The other material used is hydroxyapatite bone cement. Hydroxyapatite bone cement is inert in nature, so, has better tissue tolerance than ionomeric bone cement. Calcium phosphate or hydroxyapatite cement is self-hardening, and forms pure hydroxyapatite when set, which makes them the preferred material in ossicular chain defects. The main problem with hydroxyapatite bone cements, when used in the reconstruction of cranioplasty defects, is their prolonged setting time.
However in ossiculoplasty cases, as small amount of hydroxyapatite bone cement is used, the setting time of hydroxyapatite cement is not more than 5 minutes.
The cement is mixed with water and sodium phosphate causing a minimal exothermic reaction as described in the package insert. This mixture forms a paste that hardens to form a microporous implant within 5–8 minutes. This paste is applied, and shaped to form a stable bridge, between the incus and stapes.
Patient selection in bone cement ossiculoplasty is very important so as to obtain satisfactory postoperative hearing results and also to avoid possible undesired complications.
Bone cement ossiculoplasty is not advocated in canal wall down surgeries, in atelectatic ears, and in the presence of a cholesteatoma.
The long-term results of bone cement ossiculoplasty are still a matter of controversy.
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