14Maintaining Middle Ear Aeration and Preventing Adhesions

FWhy a prosthesis needs air around it

An ossicular prosthesis is a passive strut. It transmits sound only if the structures it connects are free to move, and that freedom depends on the one thing easiest to overlook in a reconstruction: the air around it. The middle ear is the only air-filled space in the body sealed behind a membrane, and that air is not a passive void but a working part of the hearing mechanism. An aerated cleft keeps acoustic impedance low, lets the tympanic membrane sit at its natural tension and lets the ossicular chain swing freely. Fill that space with fluid, scar or an adherent membrane and the whole transformer stiffens, adding a conductive loss before a single ossicle has been touched.

The numbers are stark. A completely non-aerated middle ear can produce a conductive loss of roughly 35–55 dB even with an anatomically intact ossicular chain, simply because the loaded, retracted membrane and stiffened system cannot transmit sound. This is why the dominant teaching of modern ossiculoplasty is that the environment, more than the prosthesis material, decides the result — and why middle-ear and mucosal status is a weighted, negative term in prognostic staging systems such as Dornhoffer’s OOPS index[2001]. A beautifully calibrated prosthesis set into an airless, scarring cleft is a reconstruction already failing.

For the surgeon, this reframes the task. Ossiculoplasty is not the mechanical placement of a strut but the restoration of a ventilated, mucosa-lined cleft in which a strut can work. Everything in this module — spacers, silastic sheeting, mucosal preservation, cartilage reinforcement and staging — serves that single goal: to send the prosthesis into an aerated space and to keep that space aerated while the ear heals.

FHow aeration is lost: retraction to adhesion

Aeration is rarely lost suddenly. It fails along a recognisable spectrum, and being able to place an ear on that spectrum is the first practical skill. Sadé’s staging of tympanic-membrane atelectasis captures it well [1981]. It begins with mild, mobile retractionof the drum — aeration preserved, the membrane re-inflating on Valsalva or suction. As negative pressure persists, the retracted drum drapes onto the incus and stapes, then reaches the promontory, and finally becomes permanently adherent: adhesive otitis media, an airless cleft in which the membrane is fixed to the medial wall and the ossicles.

The clinical importance of this progression is the loss of reversibility. Early grades re-inflate; late grades do not. Once the membrane is adherent and the air space obliterated, any prosthesis placed beneath it is pressed medially, immobilised and prone to extrusion at the membrane interface. Worse, a posterosuperior or attic retraction pocket that loses its self-cleaning is the seedbed of acquired cholesteatoma. Reading the grade therefore tells the surgeon both how much aeration there is to protect and how aggressive the protective strategy needs to be.

Two further mechanisms compound the problem at surgery. First, disease and its clearance leave denuded surfaces: stripping mucosa from the promontory, posterior mesotympanum and attic exposes raw bone that, if left apposed to another raw surface, heals by fibrous bridging rather than re-lining. Second, the mucosa itself becomes the enemy: chronic inflammation thickens it, fills the cleft with oedema and granulation, and stiffens the round-window membrane. The reconstruction must contend with both — preserving what healthy mucosa remains and keeping raw surfaces apart until new mucosa can grow.

TPreserving mucosa and clearing the niches

The cheapest aeration-protective measure costs nothing but discipline: preserve middle-ear mucosa. Mucosa is the source of the new lining that will re-aerate the cleft, and the migrating epithelium that re-lines a denuded floor comes from the islands of mucosa left behind. Aggressive, circumferential stripping in pursuit of a “clean” cavity is therefore self-defeating: it removes the very tissue that would have re-aerated the space and converts reversible inflammation into permanent fibrosis. Where disease forces mucosal removal — over cholesteatoma matrix, for instance — the surgeon plans for the denuded surface rather than ignoring it.

The second discipline concerns the windows. Both niches must be cleared and kept clear. Granulation, adhesions or packing across the round window stiffen its membrane and degrade the phase relationship the cochlea needs; tissue or cement spilling onto the oval window and footplate fixes the stapes. Clearing the oval- and round-window niches under high magnification, and protecting the footplate (commonly with a small piece of gelatin sponge soaked in antibiotic saline) while working nearby, preserves the low-impedance pathway on which the whole reconstruction depends.

• Keep mucosa. Leave every viable mucosal island; it is the seed of the new lining and the re-aerated space.
• Clear the niches. Remove obstructing tissue from the oval and round windows; do not let grafts, packing or cement cover them.
• Protect the footplate. Shield it while drilling or applying cement to avoid ototoxic spillage or inadvertent fixation.
• Pack lightly.Dense packing of the whole cleft organises into fibrous tissue that tethers the chain — use only what is needed to support, not to fill.

TSpacers and silastic sheeting

Where surfaces are denuded and apposed, the surgeon needs to keep them apart while mucosa regrows. The classic solution is an interposed inert Silastic (silicone) sheet, introduced into otologic practice by Sheehy [1973]. The principle is simple and durable: a thin sheet laid over the raw promontory and mesotympanum holds the two denuded surfaces apart, preserves an air-filled space, and lets migrating mucosa re-line the floor of the cleft rather than fusing to the undersurface of the drum. The sheet is an adhesion barrier and space-maintainer, not a prosthesis — it conducts no sound and is placed precisely to allow the things that do conduct to move freely afterwards.

Silicone earns this role by being remarkably inert. In temporal bones with Silastic left in place for between one and twenty years, Ng and Linthicum found no foreign-body reaction, no rejection and no chronic inflammation; the middle-ear space was lined by normal, continuous mucosa, and most specimens showed little submucosal fibrosis[1992]. The sheet can therefore be left as a permanent liner or, more often, used as a temporary spacer at a first stage and removed at a planned second look once the cleft has re-mucosalised. The same logic scales up to the mastoid: a large silicone sheet spanning the eustachian-tube orifice to the antrum after canal-wall reconstruction more than doubled the rate of good CT-confirmed mastoid re-aeration (about 60% versus 24% of controls), because it keeps a continuous gas pathway open while healing proceeds [2008].

Does this translate into hearing? In a comparative series of ears with chronic otitis media, middle-ear adhesions and intact ossicles, those receiving a middle-ear Silastic sheet at single-stage tympanoplasty had significantly better air-conduction, bone-conduction and air–bone-gap averages at one year than those without [2011]. The gain is modest and the evidence retrospective, but the direction is consistent with the mechanism: fewer adhesions, a more mobile reconstruction, a better gap.

Two cautions temper the enthusiasm. Silastic is a foreign body: in an actively infected or wet ear it can become a nidus for persistent discharge, and a sheet that curls, migrates or extrudes loses its benefit. And it is a barrier, not a cure — it buys time for mucosa and aeration to recover but does nothing for the eustachian dysfunction that caused the airless cleft. Sheeting is therefore an adjunct within a strategy, used in the right ear and often paired with staging, not a reflex deployed in every case.

CCartilage, staging and ventilation

The single most powerful structural defence against an airless, adherent cleft is cartilage reinforcement of the tympanic membrane. A thin fascia graft in an atelectatic ear re-retracts and re-adheres to the promontory; cartilage, by contrast, is rigid enough to resist resorption and retraction even with persisting eustachian dysfunction, yet thin enough to preserve acceptable hearing. In large series, cartilage tympanoplasty achieved drum closure in around 91% of atelectatic ears with few deep recurrent retractions, and across a thousand-patient experience it became the technique of choice precisely for the retraction-prone and high-risk ear [2003]. Palisade and island-flap cartilage techniques deliver comparable anatomical durability with hearing close to that of fascia [2009]. When ventilation is unreliable, rigidity at the drum is worth more than compliance.

The second clinician-level strategy is staging. In a denuded, atelectatic or infected ear, many surgeons deliberately separate disease clearance from ossicular reconstruction. A spacer (often Silastic) is placed at the first stage to keep the cleft aerated and surfaces apart; the ear is allowed to re-mucosalise and re-aerate over some months; and only at a planned second look — with aeration confirmed and residual disease excluded — is a prosthesis committed. The cost is a second operation; the benefit is placing the prosthesis into a known, stable, aerated space rather than gambling on one healing favourably. A staged canal-wall-up approach with temporary Silastic delivered reasonable hearing (mean air–bone gap around 21 dB) while keeping residual and recurrent cholesteatoma rates controlled [2021].

Finally, none of this substitutes for addressing ventilationitself. A prosthesis cannot generate the air it needs, so a eustachian-tube problem present before surgery is a problem the reconstruction must survive. Restoring pressure with a ventilation tube in a wet or atelectatic ear, optimising the upper airway, and — where appropriate — treating the tube directly, all act on the upstream cause that the spacers and grafts only defend against downstream.

CBuilding an aeration-protective operation

The individual measures combine into a coherent operative philosophy. The aim throughout is to deliver the prosthesis into an aerated space and to keep that space aerated until it is lined by mucosa and stable. A practical hierarchy runs from the cheapest, universal measures to the case-selected adjuncts:

No single technique is a panacea, and over-reaching with any of them does harm: dense packing scars, an unnecessary sheet in an infected ear festers, an over-thick cartilage graft dampens sound, and staging an ear that did not need it is two operations for one result. The art is matching the measure to the ear — reading the atelectasis grade, the extent of denuded surface, the mucosal and ventilation status — and accepting that, in the long run, it is a ventilated, mucosa-lined cleft, far more than the prosthesis within it, that decides whether hearing is restored or merely promised [2001].