10Prosthesis Displacement, Tilting, and Refixation

FWhen a closed gap reopens

The moment that defines a successful ossiculoplasty is the closing of the air-bone gap — the strut takes up its place between stapes and drum, sound flows again, and the patient hears. Yet that success is provisional. The prosthesis sits in a moist, mobile, biologically active cavity, and over months or years the column it forms can come undone. When it does, the gap reopens and the patient returns with a hearing loss that had seemed cured. This module is about the two principal ways that happens: displacement— the strut physically slips or tilts off its seat — and refixation— the strut stays in place but is progressively tethered and splinted by scar. Both reopen the gap; they do so by opposite mechanisms and demand different remedies.

The clue is almost always in the history. The classic pattern is the hearing honeymoon: good hearing for a year or two, then a slowly widening conductive gap in an ear that stays dry and well aerated. That trajectory, more than any single test, says the reconstruction itself has failed rather than a new disease having arisen[2001, 2021]. The first job is to distinguish a mechanical slip from a fibrotic tethering — and, before either, to be certain the relapse is not the visible tip of recurrent cholesteatoma, which changes everything. The interactive below contrasts the well-seated construct with its two failure states.

FDisplacement, tilting, and extrusion

Displacement is the commonest mechanical cause of late failure. The strut tilts away from its vertical line, its medial tip slides off the stapes capitulum (or off the footplate, in a total reconstruction), and the conductive column is broken. On imaging the prosthesis lies tilted, often with its tip fallen toward the promontory, in an otherwise clear and aerated middle ear with the rest of the chain intact[2021]. Because the cochlea is untouched, the audiogram shows a pure conductive deficit with a preserved bone line; tympanometry stays type A. The hallmark is the timing — a period of restored hearing followed by a gradual decline.

Extrusion is the related failure of the lateral interface. A rigid prosthesis head placed bare against the tympanic membrane concentrates pressure on one point; the membrane thins, the squamous epithelium migrates around the foreign body, and the head is gradually pushed laterally until it erupts through the drum, often leaving a perforation. A poorly aerated, retracting ear accelerates the whole sequence. Contemporary titanium series put the combined extrusion-or-dislocation rate at around 5% on average, though individual cohorts range widely from near zero to a third [2023]. The single most consistent protection is a disc of cartilage interposed between the prosthesis head and the drum, which spreads the load and shields the membrane; in hydroxyapatite series this dropped extrusion from 13% to under 2% [2002]. Cartilage interposition is now near-universal practice, reported in over nine in ten titanium series[2023].

TWhy struts slip: tension, coupling, and seat

Displacement is rarely bad luck; it is usually written into the reconstruction at the moment of placement. Three biomechanical variables govern whether a strut stays put: its tension, its lateral coupling, and the geometry of its seat.

Tension is the most counter-intuitive. There is a strong temptation to wedge the prosthesis in tightly so that it cannot move, but temporal-bone studies show the opposite is correct. Using laser-Doppler vibrometry on fresh bones, Morris and Bance demonstrated that loose prostheses give the best overall stapes vibration, an effect most pronounced at low frequencies, while tight prostheses buy only a marginal high-frequency gain at the cost of worse low-frequency transmission [2004]. An over-tight strut also distends the annular ligament, raises the chance of stapes subluxation or perilymph fistula, and — paradoxically — can lever itself out of position. The operating principle is therefore the loosest configuration that is still positionally stable: stable enough not to slip, loose enough to transmit. Errors of length on the order of a few tenths of a millimetre move a construct across this narrow window.

Couplingat the lateral end is the next determinant. A head that engages the malleus handle is far more stable than one resting on the drum alone, because the manubrium anchors it against the slippage and lateralisation that displace a free-floating head. Re-establishing continuity from the stapes capitulum to the malleus — the principle that gives the classic “capitulum to malleus” reconstruction its name — minimises both extrusion and displacement and is the most durable configuration available[1994]. Finally, the seat: a shaft set vertical on a square capitulum or footplate resists the tilting torque that throws a tip onto the promontory, whereas an oblique strut on a sloping seat is primed to slide. Get all three right — loose-but-stable tension, malleus coupling where anatomy allows, a vertical shaft on a clean seat, capped with cartilage — and the construct is built to last. The checklist below lets you assemble those factors and watch the stability of the construct respond.

TLate fibrotic refixation

If displacement is the failure of mechanics, refixation is the failure of biology. Healing after the index operation does not stop when the flap settles. Over months and years the middle ear lays down fibrous tissue, and the reconstruction is steadily drawn into it. Temporal-bone histopathology of retrieved grafts and implants shows the process directly: prostheses become ensheathed in fibrous tissue, provoke a foreign-body reaction, and are bridged by adhesions and, in places, by new bone, while autograft materials may resorb[2007]. The result is a strut that has not moved at all yet no longer works, because the chain around it has been splinted rigid. Sclerotic plaques compound the problem when they fix the very structures the reconstruction depends on — a tympanosclerotic ring around the oval window can immobilise a perfectly positioned footplate.

Refixation produces a different clinical signature from displacement. The prosthesis is in place on imaging, with no soft-tissue mass to suggest cholesteatoma, but the gap is back, sometimes fluctuating, and at exploration the chain feels stiff rather than discontinuous. It is favoured by exactly the milieu that the OOPS analysis identified as hostile to ossiculoplasty: poor mucosa, a non-aerated ear, and previous surgery, the same factors that load against any reconstruction [2001]. Distinguishing “the strut has slipped” from “the strut is stuck” matters, because freeing a refixed chain means lysing adhesions and paring plaque from the oval window — delicate work over the footplate — whereas a displaced strut simply needs re-seating.

CRecognising and refixing the failure

The workup of a reopened gap is the primary evaluation done again with a sharper eye. Audiometryconfirms the deficit is conductive and, crucially, that bone conduction is preserved — a sensorineural drop changes the calculus and may make revision pointless or hazardous. Tympanometry separates an aerated type-A ear from effusion or marked retraction. Microscopy and otoscopy look for a visible prosthesis head, a retraction pocket, a perforation, or discharge. Imaging earns its place chiefly to map the distorted anatomy and, above all, to exclude recurrent cholesteatoma: high-resolution CT shows a clear aerated ear with a tilted strut in simple displacement, or a soft-tissue mass when disease has returned, and non-echo-planar diffusion-weighted MRI is the most specific test for residual cholesteatoma. No surgeon should re-operate for “displacement” while a soft-tissue density sits unexamined on the scan.

Once disease is excluded, the operative remedy follows the mechanism. A displacedstrut is re-seated — assess the platform (a mobile superstructure supports a partial prosthesis; an eroded or absent superstructure over a mobile footplate calls for a total prosthesis), confirm footplate and round-window mobility, and re-build to the same rules as a primary but with an even lower tolerance for a bare interface. A refixed chain is first freed: adhesions are lysed sharply and tympanosclerotic plaque pared away from the oval window, sparing the footplate, before deciding whether the liberated chain conducts or must be replaced. Both should be counselled honestly, because revision results trail primary ones. In dedicated revision titanium series, a satisfactory air-bone gap of 20 dB or less is achieved in only about half of ears, with the location of the original ossiculoplasty among the few preoperative factors that predict success[2017]. That is a real, useful improvement for many patients — but a well-fitted hearing aid remains a legitimate, sometimes preferable, alternative for a borderline gap, and that conversation belongs in the clinic before the consent form.

CBuilding to prevent re-displacement

The best treatment for displacement and refixation is to engineer them out of the first operation, and to engineer them out again at revision. A handful of principles raise the odds of a durable result. First, treat the cause, not just the symptom. If a strut displaced because the ear was retracting and unaerated, simply re-seating it into the same hostile environment invites the same failure; ventilation, drum support with cartilage, and addressing eustachian-tube dysfunction matter as much as the prosthesis itself [2001].

Second, build for stability.Favour designs and positions that resist re-displacement — a head coupled to the malleus handle where the anatomy allows, a vertical shaft seated squarely on the capitulum or footplate, the loosest tension that is still stable, and a cartilage cap that both prevents extrusion and steadies the lateral interface [1994, 2004]. In the scarred, previously failed ear a bare interface is close to indefensible; cartilage interposition there is effectively mandatory[2023, 2002]. Third, respect the footplate.Much of the danger in correcting a refixed chain lives at the oval window, where dissecting fibrosis and tympanosclerosis off the stapes risks subluxation, fistula and sensorineural loss; if the footplate is densely fixed, it is often wiser to accept a residual gap than to chase closure into the inner ear. Approached this way, the displaced or refixed reconstruction is not a dead end but a soluble problem — one whose solution lies as much in the mechanics of how the strut was first placed as in any later heroics [2021, 2017].