14Intraoperative Tricks for Prosthesis Stabilization

FWhy prostheses move, and why it matters

A reconstruction that conducts beautifully on the operating table is worthless if the prosthesis works loose over the following weeks. Healing is not a passive process: the middle ear fills transiently with fluid and blood, pressure swings with every eustachian-tube opening, mucosa re-grows, and scar contracts. Against that backdrop a strut must hold its position, angle and contact at both ends until a fibrous capsule forms and the construct settles. Most late failures are not the material giving way but the prosthesis slipping, tilting or extruding— the air–bone gap quietly re-opens, and the patient returns with a recurrent conductive loss.

Stability is hardest to achieve at the medial end, where the strut couples to what the disease has left behind. A partial prosthesis on a present, mobile stapes head sits on a platform the crura hold steady; a total prosthesis balanced on the bare footplate has no such arch to capture it and is intrinsically prone to wander. The prognostic literature reflects this: a present mobile stapes and an intact malleus handle are among the strongest predictors of a good, durable result [2001]. This module is a practical tour of the small intraoperative tricks — cartilage shoes, footplate centring elements, judicious Gelfoam and lateral-end shielding — that keep a prosthesis seated long enough for biology to take over.

FThe bare footplate problem and the cartilage shoe

When the stapes superstructure is gone, a total ossicular replacement prosthesis (TORP) must rest its foot on the footplate itself. The footplate is small, smooth, mobile and slightly domed, and a plain prosthesis foot has nothing to capture it: each time the surgeon releases the strut, the foot tends to slide toward the oval-window rim, and the shaft tilts. An off-centre, tilted strut couples poorly and is primed to displace as the ear heals.

The most elegant answer is the cartilage shoe. A thin plate of tragal or conchal cartilage — ideally only about 200–300 µmthick so it adds minimal mass and friction — is punched with a small central hole and seated into the oval-window niche. The hole acts as a guide: it captures the foot of the TORP and holds it at the centre of the footplate, resisting lateral slip and tilt. Beutner and colleagues introduced the technique and confirmed acoustically that it stabilises a titanium TORP on the footplate, with second-look surgery showing the shoe ingrown into the niche [2008]. A prerequisite, easy to forget, is that the niche must first be cleared of granulation so the shoe seats on bare bone and ingrows; a shoe bedded into granulation does not anchor.

Longer follow-up has borne the technique out. In a single-centre series of cartilage-shoe anchorage after type III tympanoplasty, the rectangular shoe fitting snugly between the stapedial crura gave reliable coupling and low displacement over years, leading the authors to advocate it for dependable long-term total ossiculoplasty [2016]. The principle generalises: where an arch is missing, build the missing capture rather than trust a smooth foot on a smooth plate.

TFootplate centring elements and the evidence

The cartilage shoe is one way to centre a TORP foot; a second is a purpose-made footplate prosthesis (a small titanium element that seats on the footplate and accepts the foot of the strut at its centre). Both share the same logic — give the foot a defined, central seat instead of leaving it to find its own resting place — and both aim at the same failure mode of slip and tilt.

The clearest evidence comes from a comparison of TORP ossiculoplasty with versus withouta centring stapes footplate element. Adding the footplate prosthesis lowered the displacement rate and improved hearing: the air–bone gap closed to within 20 dB in about 70% of ears with the element versus 44% without, a statistically significant difference, and the mean gap reduction was correspondingly larger [2015]. The lesson for any footplate reconstruction is that a defined central seat for the foot is worth building, whether you fashion it from cartilage or place a manufactured element.

Two caveats keep the enthusiasm honest. First, any added element — cartilage or metal — sits in the sound path, so it must be kept thin and light to avoid loading the footplate or stiffening transmission. Second, centring does not excuse poor length: the foot must reach a mobile footplate centre under gentle, not crushing, contact. A perfectly centred but over-tensioned strut trades one problem for another by loading the annular ligament and raising cochlear input impedance.

TGelfoam: support without strangling the ear

Absorbable gelatin sponge (Gelfoam) is the oldest and most ubiquitous stabilisation aid. Placed into the middle ear it does several jobs at once: it supports a tympanic graft from below, steadies a strut until a fibrous capsule forms, helps with haemostasis, and holds a healing space open. Around an alloplastic prosthesis a few pledgets packed gently against the stapes can splint the construct through the vulnerable early weeks before ingrowth.

The trick is restraint. Gelfoam is not inert filler: it persists for weeks and then resorbs, and how the ear heals depends on how much was used. Dense packingis followed by fibrosis, adhesions, a retracted drum and delayed aeration — an experimental ear packed full of Gelfoam fills with new bone and fibrous tissue and the drum becomes fixed to the promontory [1983]. Clinically the same tendency appears as slower healing: a randomised tympanoplasty study found earlier epithelialisation and faster air–bone-gap recovery without middle-ear Gelfoam than with it, with no penalty in closure rate [2021]. The implication is not to ban Gelfoam but to use the lightest amount that does the job: enough to support, little enough to absorb cleanly and let the ear aerate.

There is a second, subtler hazard. Packing placed before the prosthesis is finally seated can push the strut off the footplateor alter its angle as it is inserted. The safe sequence is to seat and confirm the construct first, then add only the supportive Gelfoam needed — and to remember that a self-stable design, such as a clip PORP crimped onto the stapes head, may need no stabilising Gelfoam at all, sparing the ear the fibrotic cost.

CShielding and centring the lateral end

Stabilisation is not only a footplate problem. At the lateral end, a bare hard alloplastic head sitting against the mobile drum tends, over months, to erode through the membrane and extrude— the most visible stabilisation failure of all. The standard prophylaxis is a thin cartilage shield interposed between the head and the drum: it protects the membrane from the hard surface, broadens and softens the contact so the strut cannot pivot on a point, and helps hold length and angle. The material of the head matters too — a hydroxyapatite surface, which mimics bone mineral, is unusually well tolerated in direct drum contact, and hybrid HA-head designs reached low extrusion rates partly for this reason [1992].

Centring applies laterally as well as medially. The drum vibrates most at its centre, around the umbo and malleus handle, so the head should sit near the centre, not out at the annulus where excursion is small and the strut pivots. Where a medialised malleus pulls the head off-centre, gentle lateralisation of the malleus or a slight bend of the shaft toward the promontory restores both a central contact and an efficient line of force. The trade-off to name is acoustic: an over-large or peripherally placed cartilage shield blunts the very central input the head should capture, so the bargain is a thin, centrally trimmed shield— a small acoustic cost for a large gain in durability.

CA stabilization checklist at the microscope

The tricks above reduce to a short, ordered list of decisions once the ear is open:

• Clear the niche first. Remove granulation from the oval-window niche and footplate so any shoe or foot seats on bare bone and ingrows; bedding a strut into granulation guarantees lift-off [2008].
• Capture the medial foot.On a bare footplate, centre the foot with a thin cartilage shoe or a dedicated footplate element rather than leaving a smooth foot to slide — it lowers displacement and improves hearing [2008, 2015].
• Prefer the arch when you have it. Keep a mobile stapes superstructure and a malleus handle where possible; they are the most stable platforms an ear offers and predict the best outcomes [2001].
• Shield a bare head. Interpose a thin, centrally trimmed cartilage cap between an alloplastic head and the drum to resist extrusion, accepting the small acoustic cost [1992].
• Size for loosest-stable, then pack lightly.Seat the construct under gentle continuous contact, confirm it, then add only the minimum Gelfoam needed — dense packing slows aeration and breeds fibrosis [2021, 1983].

The final humility is the chapter’s recurring one: no trick rescues a hostile ear. Aeration, mucosal health and eustachian-tube function decide whether any stabilised construct stays healthy, and a fibrotic, non-aerated middle ear will defeat the most elegant cartilage shoe. These maneuvers give a reconstruction its best mechanical start; the biology has the last word, and the durable cartilage-shoe series make the point precisely because they were done in well-selected, well-aerated ears [2016].