2Sculpted Autograft Incus Interposition

FThe idea: the patient’s own anvil as a strut

When chronic ear disease erodes the long process of the incus, the ossicular chain falls silent: the drum still vibrates, the stapes can still rock the inner-ear fluids, but the broken link between them lets the sound energy leak away as a conductive hearing loss. The oldest and conceptually simplest repair is to take the very ossicle that has failed, lift it out, reshape it, and put it back in a new position so that it bridges the gap. This is incus interposition (sometimes called incus transposition): the bulky bodyof the incus — the part disease usually spares — is sculpted into a small strut and reseated between the handle of the malleus and the head of the stapes.

The appeal is biological. The graft is the patient’s own bone, so there is no immune rejection, no risk of transmitting disease, and no cost beyond operating time. It integrates into the middle ear with minimal foreign-body reaction, and because it reconnects the native malleus and stapes it preserves much of the chain’s natural lever, the mechanical advantage that the middle ear uses to match sound from air into fluid. Popularised for ossicular reconstruction in the era when the alternative was a block of plastic, the sculpted autograft incus became one of the defining techniques of reconstructive otology and remains a benchmark against which newer prostheses are measured [1971].

FWhen it fits: anatomy and indications

Interposition only works when the two anchors it bridges are sound. The reshaped incus must seat against something above and something below: the malleus handle (or, if the handle is gone, the drum) at the top, and a mobile stapes superstructure at the bottom. That pairing — malleus present, stapes arch present and mobile — is exactly the configuration the Austin classification calls type A, and it is the home territory of incus interposition [1971]. Lose the stapes superstructure and you can no longer interpose to the capitulum; you must reach the footplate with a total prosthesis instead.

Beyond the bony scaffold, two further conditions decide success. First, the incus itself must be reusable: its body has to be sufficiently preserved to carve a strut, and — critically — free of cholesteatoma. Second, the middle-ear environmentmust be favourable: a well-aerated cleft, healthy mucosa, a functioning Eustachian tube and quiescent disease. The graft is biological tissue living in that environment, and a poorly aerated, inflamed or fibrotic ear punishes any reconstruction, autograft or alloplastic alike. The decisive intra-operative questions are therefore: is the stapes superstructure intact and mobile, is the malleus handle present, and is the incus body healthy enough — and clean enough — to reshape?

TSculpting and seating the graft

The technical heart of the operation is the carving, and it is done off the field so that drilling debris and slips of the burr cannot injure the inner ear. After the incudostapedial and incudomalleolar joints are separated and the incus is removed, the body is held on a sucker or a small platform and shaped under the microscope with a fine diamond burr. Two features are cut. On one surface a small cup or notch is drilled to seat the head of the stapes; on another a groove or facetis fashioned to receive the malleus handle. The goal is a strut whose length and angle let it sit snugly between the two anchors without tension and without tipping — close enough to perpendicular to the drum that the lever is preserved.

Geometry is everything. Too short, and the graft loses contact and the air-bone gap persists; too long, and it splints the chain, stiffening it or even subluxing the stapes. The seated graft should rest with gentle, stable contact at both ends. Where the malleus is awkwardly medialised or foreshortened, the surgeon may instead carve the incus to bridge drum to stapes, or abandon interposition for a prosthesis that handles the geometry better. Many surgeons protect the contact points with a wisp of fascia or a sliver of cartilage and ensure the reconstruction is buttressed by a well-supported tympanic membrane so the strut is not displaced as the ear heals. The reward for this fiddly carpentry is a reconstruction made entirely of the patient’s own, perfectly biocompatible bone.

THearing results and durability

How well does it work? In a representative series of 137 sculpted incus interpositions, the mean air-bone gap fell from about 27 dB before surgery to roughly 19 dB after, with two-thirds of ears closed to within 20 dBof the bone-conduction line and — importantly — no extrusions. When those ears were re-tested more than a year later the gap had barely moved (a mean change of just −0.2 dB), confirming that the autograft is mechanically stable over time rather than slowly loosening [2005]. Reviews across the autograft literature put air-bone gap closure to within 20 dB at roughly 60–80% of ears, the spread driven largely by the middle-ear environment rather than the technique itself.

Two comparisons frame where interposition sits among the options. Against bone cement, which rebridges a short residual long process directly to the stapes, cement tends to give slightly better hearing for very short defects — in one head-to-head series 78% of cement repairs closed to within 20 dB versus 63% for interposition — but cement is only suitable when a substantial long-process stump remains, whereas interposition can span a longer gap [2013]. Against a modern titanium PORP, a randomised trial in Austin type A defects found the patient’s own sculpted incus gave air-bone gap closure comparable to the manufactured prosthesis [2017]. The autograft, in other words, is not a poor relation of titanium; in the right ear it is its equal, with a near-zero extrusion rate as a bonus.

CThe limits: resorption, fixation and cholesteatoma

The technique would dominate ossiculoplasty were it not for a handful of real limitations that have steadily eroded its popularity. The first is purely practical: sculpting takes time and skill. Carving a strut under the microscope is far slower than dropping in a pre-made titanium or hydroxyapatite prosthesis of known length, and the geometry is operator-dependent. The second is biological: an autograft is living bone in a sometimes hostile environment, and in a poorly aerated, chronically inflamed or fibrotic ear it can resorb over years, producing a delayed return of the conductive loss long after an apparently successful repair.

The third limitation is fixation. A bony graft can ankylose to the surrounding bone — the facial canal, the bony annulus, the promontory — re-fixing the chain it was meant to free and producing a new, late conductive loss that is awkward to revise. The fourth, and the most serious in cholesteatoma surgery, is the risk of reimplanting residual disease. Cholesteatoma matrix can invade an ossicle microscopically in a way that the naked eye, even under the microscope, cannot reliably exclude; reusing such an incus risks burying squamous epithelium in the reconstructed middle ear. Where the incus has been involved by cholesteatoma, surgeons therefore either avoid reusing it or sterilise it first — for example by autoclaving the harvested remnant before reimplantation, an approach shown to give acceptable long-term recurrence rates while retaining the autograft’s biological advantages [2014]. The honest summary is that interposition is superb in a clean, well-aerated, non-cholesteatomatous ear and progressively less attractive as disease, poor aeration and the need for an untainted graft mount up.

CChoosing interposition in the modern era

Set against titanium and hydroxyapatite prostheses — which offer consistent geometry, no carving and predictable mechanics — the autograft incus has lost its former dominance, and in many high-volume practices the manufactured prosthesis is now the default. Yet the technique is far from obsolete. It remains the most physiological and the most biocompatible reconstruction available, costs nothing, never extrudes through the drum the way an exposed alloplastic head can, and is invaluable where prostheses are unavailable or unaffordable. The decision is best framed not as “autograft versus prosthesis” but as a question of which ear you are operating on.

The data point the same way the experienced surgeon does by instinct: outcome is governed less by the material chosen than by the ear it sits in. Staging systems built from large ossiculoplasty series show that the surviving ossicular elements — above all an intact, mobile stapes and a preserved malleus handle — together with aeration and the absence of active disease, predict hearing far more powerfully than whether the strut is bone, titanium or ceramic [2001, 1994]. The practical rule that follows is a conservative one. In a clean, well-aerated Austin type A ear with a healthy, disease-free incus, sculpting the patient’s own anvil into a strut is an excellent, durable, cost-free reconstruction whose hearing results rival a modern prosthesis. When the incus is diseased, the ear poorly aerated, or operative time at a premium, reach instead for an alloplastic prosthesis — and reserve the elegant old technique for the ears that reward it.