Tympanoplasty

Definition
Tympanoplasty is stictly speaking the reconstruction of a tympanic membrane. It is often combined with a mastoidectomy for erradication of active chronic ear disease or with ossicular reconstruction for restoration of the conductive mechanism when this has been damaged by chronic otitis.

Classification
The Wullstein classification is the one most commonly used.
Type 1. The ossicular chain is intact. A tympanic membrane graft is used in such a way as to bridge the tympanic membrane perforation. Two types of this procedure exist:
a. Overlay technique: in this situation the epithelial layer of the tympanic membrane is removed and the graft is layed onto the denuded ear drum remnant. Skin flaps fashioned in the ear canal are positioned on top of the margins of the graft.
b. Underlay technique: with the appropriate incisions in the bony part of the ear canal flaps are elevated. The middle ear is entered and the tympanomeatal flap (posterior flap) is reflected along with the tympanic annulus and tympanic membrane remnant anteriorly. The middle ear is then filled with gelfoam and the graft is placed over the gelfoam. In the situation where there is a subtotal perforation, the malleus handle is denuded of any epithelial remnant and the graft is placed underneath the malleus handle. Most importantly the edges of the graft are placed under the tympanic remnant or the annulus anteriorly. Posteriorly, the graft lies onto the bony canal wall. The flaps are repositioned over the graft posteriorly.

Type 2. The incus is erroded. The tympanoplasty is performed in an underlay fashion in combination with a reconstruction of the ossicular chain at the level of the incus.

Type 3. Both malleus and incus are missing, the stapes is present. This is commonly encountered in cholesteatoma surgery as the result of ossicular errosion. The following posibilities exist
a. Intact external auditory canal wall
1.grafting of the tympanic membrane in so that it is in contact with the capitulum (head) of the stapes.
2.grafting of the tympanic membrane and use of an ossicular prosthesis from the head of the stapes to the undersurface of the tympanic membrane graft (this is called a partial ossicular reconstruction prosthesis = PORP).
b. External auditory canal wall has been removed
1.grafting of the middle ear space bounded by the horizontal and vertical portion of the facial nerve so that it is an aerated space in continuity with the eustachian tube. The head of the stapes is in contact with the tympanic membrane graft. This is also called a cavum minor and is most commonly done in canal wall down mastoidectomy procedures for extensive cholesteatoma.

Type 4. All ossicles: malleus, incus, stapes are missing. The stapes superstructure is present. In this situation the tympanic membrane graft is fashioned in a way to isolate the round window niche and leave the stapes footplate exposed in the ear cavity. In this way the round window is acoustically isolated from the oval window preventing maximum conductive hearing loss.

Type 5. All ossicles are missing with the exception of the stapes footplate and/or part of the superstructure. In addition, the stapes superstructure is fused to the middle ear medial wall by tympanosclerosis or the oval window is involved with otosclerosis. In a type 5 tympanoplasty the middle ear is grafted with the tympanic membrane graft in contact with the stapes, a fenestration of the horizontal semicircular canal is then performed and the graft is placed in close apposition to this fenestra. In this circumstance the acoustic energy is transmitted through this fenestra into the labyrinth. This operation is not performed today.

Indications for tympanoplasty
1. To restore the normal anatomy of the middle ear, providing a protected middle ear space, isolated from the external environment
2. To provide for the normal physiologic milleu of the middle ear: a ventilated middle ear space, free of intercurrent disease
3. As a function of the above most importantly to prevent the reccurence of active chronic otitis media with it's attendant sequelae on the organ of hearing and it's potential life threatening complications
4. To restore a conductive hearing mechanism as close to normal as possible with impovement of hearing as the ultimate goal.

Contraindications for tympanoplasty
1. The presence of active infection
2. The presence of active chronic otitis in the form of cholesteatoma involving the middle ear and / or it's related structures
3. In the face of incomplete erradication of disease by other means (surgical or medical)
4. In the presence of medical reasons contraindicating surgery




OSSICULAR RECONSTRUCTION

When the ossicular conductive chain is affected by disease, this results in attenuation of the sounds transmitted from the tympanic membrane to the oval window.
This attenuation / hearing loss reaches a maximum of 60db when the ossicular chain is disrupted.
The ossicular chain may become completely disrupted, partially disrupted or healed with a fibrous union. Alternatively, active chronic ear disease processes or other middle ear inflammation can interfere with the normal function of sound transmittion by the ossicular chain.
Common causes of ossicular chain abnormalities:

Congenital
Atresia of EAC with attendant ossicular abnormalities
Atresia or deformity of the oval window
Fusion of ossicles to surface of middle ear walls

Traumatic
Temporal bone fracture with ossicle dislocation
Direct penetrating injury through tympanic membrane
Ossicular chain disruption through fracture

Inflammatory
Chronic inflammation with ossicular errosion secondary to inflammation
Acute necrotizing inflammation with ossicular necrosis by loss of vascular supply
Cholesteatoma with errosion of the ossicles
Cholesteatoma without errosion but interference with ossicular chain
Inflammatory hyperplastic mucosa interfering with ossicular function

By far the most common cause of ossicular problems is chronic ear disease with or without cholesteatoma.
The goal of reconstructing the ossicular chain is to restore conductive hearing loss.

Contraindications to ossicular reconstruction
1. Only hearing ear
2. Presence of cholesteatoma
3. Tympanic membrane perforation
4. Deafness of the involved ear
5. Presence of active infection
6. Poor eustachian tube function

To stage or not to stage
Often times when disease in the middle ear is erradicated there is an ossicular discontinuity that follows created either by the disease process itself or iatrogenically for access to anatomically difficult areas. Data collected from a variety of operations, techniques and surgeons demonstrate that when a canal wall up mastoidectomy is performed a higher rate of cholesteatoma reccurence is observed. Therefore it has been suggested that the ossicular reconstruction be delayed to a second stage where a second look procedure functions as a method to erradicate any disease reccurence and to reconstruct. Alternatively a reconstruction can be performed at the first stage realizing that the rate of failure in such a situation is higher. In a canal wall down procedure the rate of failure is much lower and the magnitude of ossicular reconstruction is also more limited than a canal wall up procedure.

Prosthetic materials used for ossicular reconstruction

Autologous
sculpted incus as partial ossicular reconstruction for absence of incus long process
intact incus / inverted for total ossicular reconstruction in absece of stapes superstructure
auricular / tragal cartilage

Homologous cartilage
banked cartilage either from rib or from knee which has been radiated and can be sculpted
Homologous middle ear grafts
not used any more secondary to risk of transmitting jacob-kreutzfeld, aids and other diseases. These were harvested from fresh cadavers and stored in sterile, antisceptic solutions.
Artificial grafts
hydroxyapatite and derivatives (flex H/A)
polytetrafluorethylene and derivatives (polytef)
polyethylene
metal

Types of ossicular defects
There are only a limited number of combinations of ossicular defects that can be observed:
Incus Stapes Malleus reconstruction type
absent present present sculpted incus, PORP
absent absent present TORP
absent absent absent TORP + cartilage
absent present absent PORP + cartilage
absent incus in this table means absent superstructure, absent malleus means absent long malleolar process

In search of the ideal graft
After several attempts at different artificial materials the newer ceramics and plastics seem to have the best potential properties. These include:
excellent performance (high stiffness to mass ratio)
tolerance by environment without inflammatory responce
limited rejection
improved incorporation
absent toxicity

In limited situations the use of a sculpted incus is indicated, this is most commonly encountered when the long process of the incus is erroded but the malleus and stapes remain intact.

Cartilage as a graft may have excellent properties circumstances where a small defect needs to be bridged. However cartilage is exceptionally susceptible to infection and resorbs over time.
Performance .

The performance of a prosthesis depends on:
Physical characteristics: stiffness, maleability
Status of the remainder of the conductive mechanisms
Angles between the proximal and distal anchoring points
Healing prossesses resulting in fibrous union, fibroses, adhesions and misplacements
Complications
Failure of an ossicular reconstruction could be due to one of the following:
Extrusion of the prosthesis through the tympanic membrane or down the eustachian (rarely)
misplacement
adhesions
fibrosis and resorption
Extrusion for total ossicular reconstruction prosthesis is higher than partial ossicular reconstruction prosthesis.
Older materials have a higher extrusion rate than newer more biocompatible materials.
To avoid extrusion the procedure has to be attentive to technical detail:
Use of precise length proshtesis
Avoid reconstructing in inflammation or disease
Cartilage interface with tympanic membrane
proper positioning and cushioning in the middle ear