6TORP onto the Stapes Footplate

FWhen the superstructure is gone

Chronic ear disease destroys ossicles from the most vulnerable point outward. The long process of the incus goes first; later the delicate arch of the stapes — its capitulumand the two slender crura — can erode away entirely, leaving only the footplate sitting in the oval window like a tiny mobile trapdoor. Once the superstructure is gone there is nothing left for a partial prosthesis to perch on, and the reconstruction must reach all the way down to that footplate. This is the job of a total ossicular replacement prosthesis (TORP): a single strut spanning from the footplate to the drum or malleus, a modern realisation of the old columella idea of one bone bridging the cleft [1956].

The medial coupling point is what names the device. A PORP rests on a present, mobile stapes head; a TORP reaches past the missing arch to the footplate itself. So the decision between them is made at one moment at tympanotomy, by answering a single question: is there a usable stapes superstructure?If the arch is intact and mobile, preserve it and reconstruct with a PORP; if it is gone, reach the footplate with a TORP. The same finding that mandates the TORP — an absent superstructure — also tells you something sobering, because losing the arch is itself a marker of more aggressive disease and an independently worse prognosis [2001].

The technique that follows is therefore not just “a longer PORP.” Reaching the footplate changes the mechanics, the failure modes and the tricks needed to make the reconstruction hold. The footplate is a flat, slippery target with no socket; the drum is a thin membrane that resents a rigid head pressed against it; and the strut is long enough that small errors of angle or length are magnified. Good TORP surgery is, at heart, the art of taming those two free ends.

FTwo free ends: why the TORP is unstable

A PORP enjoys a built-in advantage the TORP lacks. Its foot drops onto the cup-shaped head of the stapes, a natural socket that centres and steadies it. A TORP has no such luxury. Its foot balances on the smooth, almost featureless surface of the footplate, and the longer the shaft, the more any small tilt is amplified at the base. The two ends of the prosthesis are, in effect, both free: a head that wants to extrude laterally through the drum, and a foot that wants to tilt and slide medially off the footplate.

These are not theoretical worries. In the largest synthesis of the literature — a meta-analysis of forty studies and more than four thousand ears — PORPs significantly out-performed TORPs at chain reconstruction, with a combined risk ratio of about 1.28 in favour of the partial prosthesis [2013]. Part of that gap is mechanical, the price of the unstable footplate interface and the longer lever arm; part is selection, because the ears that need a TORP have lost more to disease. Whatever the mix, the message for technique is clear: the surgeon must actively build in the stability that a PORP gets for free. The widget below walks through how, assembling the construct one stabilising step at a time.

TCentring the foot on the footplate

The medial end is where TORP surgery has advanced most. Left to itself, a prosthesis foot on a bare footplate is poised to slip; the solution is to manufacture a socket the anatomy no longer provides. The most elegant version is the cartilage “shoe”: an oval plate of cartilage, roughly 2.5 by 3.5 mm, with a small central hole punched through it, seated in the oval window niche so that its hole grips and centres the foot of the prosthesis over the middle of the footplate [2008]. A grooved titanium footplate plateachieves the same end with a manufactured channel that captures the shaft. Either way, the principle is identical — convert a flat target into a socket.

Two cautions govern this step. First, do not violate the footplate. The temptation to drill a well into it, or to seat the foot deeper for security, must be resisted: breaching a mobile footplate invites perilymph fistula, sensorineural loss and vertigo, and sacrifices the compliance of the annular ligament that the whole system depends on. The prosthesis is centred on top of the footplate, never driven into it. Second, the centring graft must stay compliant. Packing the oval niche rigidly — with bone pate, say — risks fixing the prosthesis and the footplate together, abolishing the very mobility the operation is meant to restore. A thin cartilage shoe or a precise grooved plate centres without splinting.

TThe head, the cartilage cap and tension

With the foot centred, attention turns to the lateral end. Two decisions matter: what the head leans on, and how tightly the whole strut is sized. The first decision is where to couple the head. Wherever the malleus handle survives, the head should be angled toward it rather than left on bare drum. The malleus offers a stable proximal fixation point and preserves part of the native lever, and cadaveric work shows that malleus-coupled assemblies transmit vibration more efficiently than drum-coupled ones — a principle that carries directly to the footplate-to-malleus TORP [2004].

The second decision is the cartilage cap. A bare, rigid alloplastic head pressed against the thin tympanic membrane concentrates its load on a tiny patch of epithelium; over months that point load drives pressure necrosis, the drum thins, and the prosthesis migrates and finally extrudes. Interposing a thin disc of tragal or conchal cartilage spreads the load over a firm, resorption-resistant cushion and keeps the metal off the epithelium, dropping extrusion to low single digits. Whether the cap is strictly mandatoryis genuinely debated — series of bare titanium heads in favourable, well-aerated ears report acceptably low extrusion, the rare failures linked to drum retraction rather than the head itself [2014]. The pragmatic position is that a thin cap costs almost nothing acoustically and buys real protection, so most surgeons use one routinely in the reconstructed, previously diseased ears that need a TORP.

Underlying both decisions is tension. The annular ligament that suspends the footplate supplies most of the conductive system’s compliance, and a TORP that is too long over-tensions it — stiffening low-frequency transmission and risking footplate subluxation — while one that is too short loses contact and leaves the gap open. The target is the time-honoured one: the loosest length that is still positionally stable, with a touch of shaft flexibility rather than a rigid wedge. Centred foot, malleus-leaning head, thin cartilage cap, loosest stable fit: four moves, each countering one of the TORP’s built-in weaknesses.

CWhat the footplate device buys you

Does stabilising the foot actually change outcomes, or is it surgical fastidiousness? The clinical evidence says it matters. In a series of 161 titanium TORP ossiculoplasties, adding a titanium stapes footplate prosthesis— a centring device that seats the foot over the oval window — closed the air-bone gap to within 20 dB in roughly 70% of ears, versus about 44% when the foot was left on the bare footplate, with fewer prosthesis displacements [2015]. A separate titanium series using a footplate shoe found the same direction of effect on the magnitude of closure: a mean air-bone gap reduction of roughly 22 dB with the shoe against about 13 dB without it, and a smaller residual gap that held up over longer follow-up [2014].

Read together, these series make a coherent case. Centring the foot is not a flourish; it converts the TORP’s single greatest mechanical liability — an unanchored base on a slippery footplate — into a stable, reproducible interface, and the hearing numbers move with it. The same logic underlies the cartilage cap and the malleus coupling: every one of these manoeuvres trades a small amount of operative effort for a measurable reduction in the construct’s tendency to fail.

CCounselling and the honest ceiling

However well the construct is built, the surgeon must counsel against the right benchmark. The meta-analytic truth is that TORPs close the gap less reliably than PORPs, and no amount of technical polish fully erases that difference [2013]. The reason is twofold and worth stating plainly: the footplate interface is inherently less stable than a stapes-head interface, and the absent superstructure that forces a TORP is itself a signature of more severe disease and a worse host bed [2001]. The device is being asked to do a harder job in a less forgiving ear.

Three practical rules follow. First, preserve any usable arch: if even a stub of mobile superstructure remains, a PORP onto it will usually out-perform a TORP, so never sacrifice a superstructure to standardise the operation. Second, optimise the host bed— aeration, mucosal health, a functioning Eustachian tube, quiescent disease — because these govern outcome more than the choice of prosthesis, and a hostile ear may be better served by staging the reconstruction. Third, when the superstructure is genuinely gone, do the TORP well: centre the foot, recruit the malleus, cap the head and size for the loosest stable fit, and tell the patient honestly that a real but more modest hearing improvement is the expected result. The TORP onto the footplate is the correct device for a difficult situation; respected for what it is, and built with its instability in mind, it restores serviceable hearing to ears that would otherwise have none.