The ideal material for ossicular reconstruction should meet three principal criteria. First, the material must be stable in the middle ear environment. There should be minimal if any rejection phenomena to avoid any granulation tissue formation or subsequent degradation of the reconstruction. Second, the material should present no risk of interaction in the middle ear environment. in reference to this, the reconstruction should minimize the risk of infection or deleterious chemical reaction in the middle ear. Finally, the prosthetic material should allow stable coupling to the remaining ossicles to maximize sound transduction through the reconstructed chain. The options for prosthetic materials comprise auto-grafts, homografts, and allografts.
The autograft incus is clearly well tolerated in the middle ear environment. Long-term results with this type of prosthesis abound in the literature and have proven its stable results over time.20,21 Because of its nature as an autograft, there is no risk of rejection or transfer of nonhost disease in a reconstruction. The only caveats for using an autograft are the stability of the coupling and the risk of cholesteatoma within the haversian canals.22 In a recent review by Goldenberg and Emmet,7 the autograft prosthesis was shown to be in frequent use in the united States.
Homografts have similar benefits to autografts. These materials present no significant risk of rejection in the middle ear, and their use has been validated in numerous studies to date.4 As with the autograft, homograft stability and effective coupling are dependent on the shape used in reconstruction. In contrast to autografts, however, homografts do bring an additional set of risks. of particular concern is the risk of transmission of viruses or viral particles (prions). Although there are no reports in the literature of transmission of prions or HIV, the theoretical risk has greatly hampered use of homografts in the united States since the mid-1980s. Newer techniques of sterilization have been reviewed elsewhere5 and might usher in a resurgence of homograft use in the middle ear.
options for allografts include multiple plastics, ceramics, metals, and combinations of any of the above, with HA and titanium representing the most commonly used materials for allograft prostheses. Introduced in the 1980s by Grote,23 HA is a calcium phosphate compound that comes in both dense and porous forms. The dense form is well tolerated by the tympanic membrane in terms of extrusion rates but is hard to shape or cut. The porous form is easier to cut and shape but induces more osteoblast activity and has a higher rate of extrusion when in contact with the tympanic membrane.2 Because of its induction of osteoblastic activity, porous HA is considered bioreactive. As a totally synthetic material, HA carries no risk of disease transmission to the recipient site. Numerous studies regarding implants of this material have been published to date and have shown generally good results.19,24 Although dense HA has been proven safe when placed directly against the tympanic membrane,2 we espouse covering the prosthesis head with cartilage to prevent extrusion in the presence of continued poor eusta-chian tube function (Fig. 20-4). Placement of this firm and well-tolerated substance between the tympanic membrane and the prosthesis maximizes protection and controls the extrusion rate in even the most inhospitable middle ears.
The second allograft material worth mentioning is titanium. used for years in Germany as the preferred material for reconstruction, titanium is gaining significant attention in the united States as an
implant material. Unlike HA, titanium is classified as a bioinert material. It poses little risk of rejection in the middle ear environment and has been clearly demonstrated to be of no risk for chemical reaction or degradation in the middle ear.25 Unlike HA, use of titanium prostheses mandates the use of cartilage in any reconstruction. Because the titanium prosthesis is machined or pressed, its edges are much sharper than dense HA and, subsequently, pose a higher risk of extrusion. In addition to this caveat, the other issue with titanium is shaping and trimming the prosthesis. Many of the currently marketed products require separate cutting instruments when these prostheses are utilized.
To date, the senior author (J.D.) has implanted over 100 titanium prostheses and over 500 HA prostheses, and good results have been obtained from both. The authors have found both materials to be well tolerated in the middle ear and to result in very low extrusion rates; however, we espouse the copious use of cartilage and believe this helps account for our success with either type of prosthetic material. Although we prefer HA against the tympanic membrane, we appreciate the outstanding coupling of a titanium bell at the stapes superstructure. For this reason, the Dornhoffer titanium bell PORP (Gyrus ENT Division, Memphis, TN) is our choice for partial reconstructions (Fig. 20-5). For total reconstructions, we utilize the Dornhoffer HAPEX TORP (Gyrus ENT Division) when the malleus is present and the Kurz Tübingen type (TTP) aerial (Kurz Medical, Tübingen, Germany) when the malleus is not present or when the tympanic membrane is significantly lateralized. All of these prostheses have a center of gravity over the intended vector of the stapes and allow good coupling in the planned environment.
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