Implant Design

Design of the prosthesis requires understanding of the acoustic mechanisms involved in the middle ear, as well as the anatomic and acoustic changes that occur with reconstruction. Reconstructing a defect in the ossicular chain requires adequate conduction of sound energy from the tympanic membrane to the stapes footplate. This must take advantage of the lever mechanisms inherent in the middle ear and transmitting the energy in a piston-like manner from the manubrium of the malleus to the footplate. Many designs have been developed that accomplish this goal (Fig. 19-1).

Adequate function of this design depends on maintaining contact with the stapes superstructure or footplate, as well as over the surface area in contact with the tympanic membrane. Poor outcomes result from movement at the lateral attachment of the prosthesis, movement at the medial

Torp Tympanic Membrane

FIGURE 19-1 Prosthesis designs: (A) Bojrab universal; (B) Grace titanium adjustable designed by Bojrab; (C) hydroxyapa-tite incus strut and incus-stapes strut designed by Kartush; (D) Polycel PORP and TORP designed by Sheehy; (E) Micro-PORP designed by Bojrab.

FIGURE 19-1 Prosthesis designs: (A) Bojrab universal; (B) Grace titanium adjustable designed by Bojrab; (C) hydroxyapa-tite incus strut and incus-stapes strut designed by Kartush; (D) Polycel PORP and TORP designed by Sheehy; (E) Micro-PORP designed by Bojrab.

attachment, extrusion of the prosthesis, or from poor eustachian tube function.26

Failure of ossicular chain reconstruction arises from two main causes: extrusion, and movement of the prosthesis (Table 19-3). To overcome this, the design of the prosthesis should decrease these risks (Table 19-4). Many implant designs have been developed with myriad materials, shapes, sizes, and weights to be used in the middle ear. success seems comparable among many of these. Other factors contribute to the success of ossicular chain reconstruction, such as eustachian tube function and aeration of the middle ear. The principles applied to improving tympanoplasties can contribute to ossi-culoplasty success by preventing atelectasis or later-alization. These include proper graft placement, grommet insertion when needed to ventilate middle

Table 19-3 Reasons for Ossicular Reconstruction failures

Disease

Prosthesis failure

Recurrent or residual middle ear disease

Eustachian tube dysfunction

Extrusion

Improper size Design flaw

Movement

At lateral connection At medial connection ear, using Silastic sheeting to maintain middle ear, and staging the reconstruction when necessary.

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Responses

  • Sarah
    Does the kartush incus strut prosthesis go in the middle ear space or tympanic membrane?
    3 years ago

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