5PORP onto a Mobile Stapes Superstructure

FThe best seat in the middle ear

Of all the ways an ossicular chain can be broken, one is comparatively kind to the surgeon: the incus is gone or eroded, yet the malleus is present and the stapes superstructure is intact and mobile. In the classification that otologists still reach for, this is Austin type A— malleus present, stapes present — and it is the configuration that predicts the best hearing results in all of ossiculoplasty [1971]. The reason is the small, mobile knob at the top of the stapes: the head, or capitulum. It offers a stable, freely moving seat on which a partial ossicular replacement prosthesis (PORP) can rest, bridging the gap back to the drum or the malleus handle and restoring the chain with a single, short strut.

This module is about that operation: how to seat a PORP on a mobile stapes head, anchor it laterally, protect it with cartilage, and get the tension right. It is a technique worth doing well, because the anatomy it depends on — a present malleus and a mobile arch — is exactly the anatomy that the outcome data single out as the strongest predictor of success [2001, 2006]. Get the construct right and you are working with the grain of the best evidence in the field.

FWhat a PORP is and why the stapes head matters

A PORP— partial ossicular replacement prosthesis — is a strut that replaces the partial defect in the chain: it spans from the lateral structures (the drum or malleus handle) to the head of the stapes. Its sibling, the TORP (total ossicular replacement prosthesis), is needed when the superstructure is gone and the strut must rest directly on the footplate. The single anatomical fact that decides between them is therefore the presence or absence of a usable stapes arch. When the superstructure is present and mobile, a PORP is the natural and superior choice; when it is absent, a TORP is unavoidable.

Why does the head matter so much when most of the sound energy is delivered at the footplate? It is a fair question, and the honest answer is that the arch itself adds little acousticadvantage — the theoretical gain from the superstructure is small [1998]. Its value is mechanical. The capitulum is a rounded, mobile knob that a head plate or a cupped autograft socket can cradle: a broad, stable, low-profile seat that keeps the strut short and lets it move physiologically. A TORP, by contrast, must balance on the flat, slippery footplate, where it is more prone to tip, slip and migrate. So the stapes head earns its reputation not by amplifying sound but by giving the reconstruction a place to stand.

TBuilding the short columella

The construct a PORP creates is called a short columella: a single vertical pillar from the lateral chain to the stapes head, in contrast to the longer, more precarious columella a TORP builds to the footplate. Two design choices define it. The first is the lateral anchor. When the malleus is present — and the data say its presence is the most powerful single predictor of success — the head plate is best notched or grooved onto the manubrium. Kartush described this capitulum-to-malleus strut precisely because the malleus handle behaves like a central tent-pole: it captures the prosthesis, aligns the vibratory vector and minimises both extrusion and displacement [1994]. Where the malleus is foreshortened or medialised, the head plate instead couples beneath the drum, ideally near the umbo, where the membrane vibrates most; eccentric placement out toward the annulus sits where the drum barely moves and is prone to slip.

The second choice is the vector. The shaft should run as vertically as possible, perpendicular to the plane of the footplate, so the prosthesis drives the stapes in a clean piston-like motion. An angulated strut couples poorly and tends to walk off the capitulum or subluxate the arch during the pressure swings of normal middle-ear life. Many surgeons, when remodelling an autograft incus, deliberately drill a small acetabulum— a shallow socket — into the prosthesis so it cups the capitulum: neither so shallow that it slips nor so deep that it grips and damps the natural micromotion the chain depends on. The widget below lets you switch between the malleus-anchored and drum-coupled forms and toggle the protective cap.

TThe evidence: why PORP beats TORP

The claim in the standfirst — that this is the technique behind the best ossiculoplasty results — is not rhetoric. When a mobile superstructure is present, a PORP closes the all-important air-bone gapmore reliably and more durably than a footplate TORP. The largest synthesis is a meta-analysis of 40 studies and 4,311 ears: PORP was significantly more effective at closing the gap to within 20 dB (combined risk ratio 1.28, 95% CI 1.17–1.41) and significantly more stable on long-term follow-up, with the advantage attenuated only in staged and cholesteatoma subgroups [2013]. Yung’s long-term audit told the same story from a different angle: a present malleus made an ear more than six times more likely to succeed at six months, and an absent stapes was an unfavourable factor [2006].

Two caveats keep this honest. First, when the head-to-head numbers control for the prosthesis material and the middle-ear environment, the gap narrows: Dornhoffer and Gardner found PORP and TORP air-bone gaps that were statistically indistinguishable (13.4 versus 14.0 dB), with the malleus and the middle-ear environment doing the heavy lifting rather than the prosthesis type per se[2001]. Second, the durability advantage of the PORP is partly a story about stability: a strut that sits in a stable capitular cradle drifts less than one balanced on the footplate. The practical synthesis is straightforward — when you have a mobile superstructure, use it; the favourable anatomy and the stable seat together deliver the field’s best results.

CSeating, tension and the cartilage cap

The craft of this operation lives in three details. The first is length and tension. The strut must bridge the capitulum to the lateral anchor with light, even contactat both ends — neither compressed nor distracted. A PORP that is too long lifts and tilts the drum, lateralising it and pulling it into retraction over time; one that is too short leaves a loose coupling that transmits little. Trial lengths are seated and the drum observed: it should sit naturally over the construct, not tented up by an over-long strut.

The second detail is the cartilage cap. A rigid head plate resting directly on the thin drum concentrates load on the epithelium and, over months, erodes through and extrudes. Interposing a thin disc of tragal or conchal cartilage — shaved toward roughly 0.5 mm — spreads that load, keeps the hardware off the epithelial surface, and is the near-universal final move of the operation. The clinical proof is clean: with a hydroxyapatite prosthesis, extrusion fell from 13.2% without a cap to 1.9% with one, and the hearing gain was no worse [2002]. Resist the urge to over-protect: a heavy, oversized cap adds mass that damps the high frequencies the reconstruction is meant to restore. The rule is the thinnest cap that still keeps the head plate off the drum.

The third detail is the one beginners under-weight: the environment. The most beautifully seated PORP will fail in a wet, atelectatic, poorly ventilated ear, because the statistical staging of ossiculoplasty shows the middle-ear environment outweighs the prosthesis itself [2001]. So the final check is not just “is the construct stable” but “is this an ear that will keep it stable” — dry, aerated, with healthy mucosa. Where it is, the favourable anatomy delivers what the evidence promises.

CWhen the favourable ear turns awkward

A present, mobile superstructure is the ideal, but it is not always cooperative. Chronic inflammation or prior surgery can leave the arch inferiorly rotated, medialised or fibrosed, sitting deep in a shallow middle-ear cleft where a PORP cannot seat squarely on the capitulum. Forcing a steeply angulated PORP onto a tilted head is a false economy: it couples poorly and slips. In these awkward ears a TORP that bypasses the archand rests on the footplate can give comparable results to a PORP and avoid an unstable construct — a well-seated TORP beats a badly seated PORP [2015]. What is almost never justified is removing a healthy mobile superstructure to make room: that discards the very structure the outcome data prize, and violating a mobile footplate to ease seating risks a sensorineural loss and a perilymph leak.

A workable routine falls out of all this. Confirm mobility of the superstructure and footplate. Measure the gap and pick a length that bridges it without compression. Seat the head on the capitulum with a near-vertical shaft, and anchor it to the malleus handle where one is present or beneath the centre of the drum where it is not. Cap the head with a thin cartilage disc. Then re-check stability and aeration before the flap goes back. Done this way, with the grain of the anatomy and the evidence, the PORP on a mobile stapes head delivers the most reliable, most durable hearing result that ossiculoplasty has to offer [2013, 1994].