9PORP Versus TORP: Matching Prosthesis to Residual Chain

FOne anatomical fact, two prostheses

When the ossicular chain has been broken by disease, the surgeon must rebuild a bridge from the vibrating tympanic membrane to the cochlear fluids. The market offers a confusing array of prostheses, but the first and most important decision is binary, and it turns on a single anatomical fact: is the stapes superstructure still there? The stapes has two parts — the superstructure (the two crura meeting at the head, or capitulum) and the footplate sealing the oval window. If the superstructure survives intact and mobile, a partial ossicular replacement prosthesis (PORP) can rest on the stapes head. If the superstructure has been destroyed but the footplate remains mobile, only a longer total ossicular replacement prosthesis (TORP), seated directly on the footplate, will reach.

This is the practical heart of Austin’s classic classification, which groups ossicular defects by the presence of the malleus handle and the stapes superstructure precisely because those two features dictate the geometry the reconstruction must reproduce [1971]. Everything that follows — prosthesis length, stability, expected hearing — flows from this one observation made in the oval window niche. The explorer below lets you toggle the superstructure and watch the matching prosthesis change.

FWhat a PORP and a TORP actually connect

The names are descriptive once unpacked. A PORP replaces only part of the chain: it bridges from the malleus handle (or, if the malleus too is gone, from the drum or a cartilage graft) down onto the head of the intact stapes. The native stapes therefore remains in the sound path, doing the final job of driving the footplate. A TORP replaces the chain totally: it spans from the malleus/drum all the way to the stapes footplate, becoming the entire columella because no usable superstructure is left to borrow.

Two further principles apply to both. First, couple to the malleus handle whenever it is present: a malleus-to-stapes (PORP) or malleus-to-footplate (TORP) construct retains some of the native lever and is more stable than a prosthesis terminating only on the drum. Second, protect the drum with a cartilage shieldwherever a rigid head abuts a thin membrane, to curb the slow extrusion that plagues synthetic heads. Neither “P” nor “T” specifies a material — titanium, hydroxyapatite and polymers are all made in both lengths.

TWhy the stapes superstructure decides

It would be tidy to say the superstructure simply gives the prosthesis somewhere to sit — and it does — but its real significance runs deeper. The superstructure is a marker of disease severity. An intact crural arch usually means the destructive process spared the medial chain; an absent arch usually means a more aggressive cholesteatoma or chronic inflammation that has eroded further [1971]. So the moment you reach for a TORP, you are typically operating in a worse ear from the outset, and prognostic staging systems weight this accordingly: the Middle Ear Risk Index treats a more denuded ossicular status as a higher-risk situation [1994], and the OOPS index likewise loads the surviving remnant as a dominant predictor of the eventual hearing result [2001].

Mechanics compound the disadvantage. A TORP is longer, and it is balanced on the small, flat footplate rather than nestled in the cup of the capitulum. That makes it intrinsically more liable to tilt, slip, and extrude, and harder to tension correctly: too loose and it loses contact, too tight and it loads the annular ligament and stiffens the footplate. A PORP, shorter and seated in a defined cup on a structure that already moves as a unit, is simply an easier and more forgiving reconstruction. The superstructure, in other words, predicts the outcome on two grounds at once — it reflects how much disease the ear has suffered, and it determines how demanding the rebuild will be.

TWhat the comparative evidence shows

The literature is consistent on the headline: PORP outperforms TORP on average. A meta-analysis pooling comparative series found that partial prostheses closed the air-bone gap successfully significantly more often than total prostheses, with a combined risk ratio of 1.28 (95% CI 1.17–1.41) favouring PORP [2013]. Long-term clinical experience tells the same story and adds a sobering note about durability: success rates drift downward with time for both, but the TORP curve sits well below the PORP curve at five years. The chart below sets the long-term figures beside a contrasting scenario discussed in the next section.

Read these numbers correctly. They do notprove that a TORP is a bad prosthesis, nor that you should ever choose a PORP when the superstructure is gone — you cannot, because a PORP has nothing to sit on. They show that the defecta TORP is called upon to fix is inherently harder. The fair comparison is not “PORP versus TORP” in the abstract but “a present superstructure versus an absent one” — and the present superstructure wins because it is the better starting point, as much as because it allows the simpler prosthesis [2001].

CWhen the rule bends: present but unfavourable

The binary rule — superstructure present → PORP, absent → TORP — is the right default, but the experienced otologist knows when to bend it. Occasionally the superstructure is intact yet geometrically unfavourable: rotated inferiorly under an overhanging facial ridge, or set in a shallow middle-ear cleft, so a PORP repeatedly tilts and will not seat squarely on the capitulum. In that situation a TORP placed onto the footplate alongside the intact superstructure can give a more stable, better-coupled construct than a wobbling PORP. A prospective comparison of titanium reconstructions in ears with an intact stapes found that TORP-through-the-intact-arch produced hearing results not significantly different from PORP and stable beyond a year, making it a legitimate alternative when the anatomy fights the partial prosthesis [2015].

Going further, several groups have shown that a footplate-seated TORP is feasible independent of whether the superstructure is present. In one series using a tympanic-membrane/malleus-to- footplate TORP even where the stapes arch survived, the air-bone gap closed to within 20 dB in 83% of ears with a mean closure of 27 dB [2021]. Comparative work in superstructure-present ears similarly finds that partial and total prostheses can converge when placed on the same favourable anatomy [2020]. The lesson is not that the superstructure is irrelevant — on average it matters greatly — but that when a present superstructure cannot be used stably, dropping to the footplate is wiser than forcing an unstable PORP or, worse, amputating a healthy stapes arch to tidy the field.

CA choosing routine at the microscope

With the oval window niche cleared and the chain inspected, the decision can be made in a few seconds:

• Is the stapes superstructure intact and mobile? If yes and it offers a stable seat, default to a PORPfrom the malleus/drum to the stapes head — the shorter, more forgiving, higher- yield reconstruction [2013].
• Is the superstructure destroyed, with a mobile footplate surviving? Use a TORP from the footplate to the malleus/drum. Expect a harder rebuild and counsel accordingly — this defect starts from a worse baseline [2001].
• Is the superstructure present but unstable (inferiorly rotated, crowded cleft, PORP keeps tilting)? Consider dropping to a footplate-seated TORP rather than forcing the PORP; results can match a PORP in this setting [2015, 2021]. Never sacrifice a healthy mobile superstructure merely for access.
• Is the footplate fixed or absent?Then neither standard prosthesis transmits — the problem is now at the footplate, and a staged stapes procedure or alternative strategy is needed before columellar reconstruction makes sense.
• Whatever you place, optimise the constants. Couple to the malleus when present, cap a rigid head with cartilage, set the tension to firm-but-mobile, and remember that aeration and mucosal health govern the result more than the letter on the prosthesis [1994].

The mature view is therefore neither dogmatic nor casual. The presence or absence of the stapes superstructure is the correct first question and a powerful predictor of success, but it is a guide to the default prosthesis, not an immovable law. Match the prosthesis to the residual chain, bend the rule only for a clear mechanical reason, and counsel the patient that a TORP ear — because of the disease that emptied the oval window niche — has further to climb [2013, 2020].