6Impact of Malleus and Stapes Status on Results

FTwo structures that decide the result

Of all the variables a surgeon weighs before reconstructing the ossicular chain — the material of the prosthesis, the technique, the aeration of the middle ear, the activity of disease — two anatomical findings stand out for how powerfully they predict the hearing result: whether the malleus handle is still present, and whether the stapes superstructureis still present and mobile. These are the two sturdier ends of the chain, the survivors that chronic disease tends to spare while it dissolves the more vulnerable incus between them. They are so prognostically central that the oldest and most enduring classification of ossicular defects, Austin’s, is built entirely from their presence or absence [1971].

Austin sorted ears into four quadrants. Type A— malleus present, stapes superstructure present — is the most favourable; type D— both absent — is the least. Types B (malleus only) and C (superstructure only) sit between. This is not an arbitrary scheme: it captures, in two binary observations, most of what can be known about the difficulty of the reconstruction and the hearing the patient can expect. The remainder of this module asks why each structure matters, how much it matters, and how to translate that into honest counselling and sound operative planning.

FWhy a retained malleus helps

The malleus earns its prognostic weight in three distinct ways. First, it is the central tent-pole of the drum: the handle gathers the conical vibration of the whole tympanic membrane and funnels it, at the umbo, into the ossicular pathway. A reconstruction that engages the malleus handle taps this concentrated motion at its source; one that ends on the bare drum samples a less favourable part of the membrane. Second, the malleus provides lateral support: it gives the head of a prosthesis a firm structure to lean against, so the construct does not tip, slip or rotate as middle-ear pressures fluctuate and the drum heals. Third, it preserves the lever vector — a strut running from the stapes up to the malleus handle keeps the line of force close to the natural axis of the ossicular lever, rather than driving the stapes obliquely from a column planted on the drum [1994].

Clinicians have long recognised this. Black’s SPITE prognostic scheme treats the presence of the malleus as a critical surgical and prosthetic determinant of success[1992], and Kartush’s Middle Ear Risk Index weights ossicular status, including the malleus, as a core variable [1994]. De Vos and colleagues, analysing 140 titanium ossiculoplasties, found the absence of the malleus to be an adverse prognostic factor on multivariate analysis, attributing its benefit to both the stability it lends the construct and the catenary-lever acoustic gain it restores[2007]. The recurring message across these schemes is the same: keep the malleus, use the malleus, and the reconstruction is both more stable and better aligned.

TWhy a present stapes superstructure helps

The stapes superstructure earns its keep along a different axis. Its own acoustic contribution is modest: almost all the energy that reaches the cochlea passes through the footplate, whether the prosthesis sits on the stapes head or directly on the footplate. The real prize of a present, mobile superstructure is geometry and stability. An intact arch lets the surgeon couple a shortpartial ossicular replacement prosthesis (PORP) to the stapes capitulum rather than balancing a tall total prosthesis (TORP) on the bare footplate. The short construct is shorter, lighter, easier to seat, less likely to tip, and far less prone to displacement — which is precisely why series of PORPs to a present superstructure reliably outperform series of TORPs to the footplate[2001].

There is an important corollary that keeps the picture honest. Because the superstructure’s contribution is largely about the construct rather than intrinsic acoustics, a meticulous TORP technique can sometimes match or beat a routine PORP even when the superstructure is present. Vincent and colleagues, studying 585 ears with an absent incus but an intact mobile malleus and stapes, found a short PORP onto the stapes head closed the air-bone gap to within 20 dB in 70.4% of ears (mean gap 13.1 dB), while a TORP combined with deliberate malleus relocation and Silastic banding reached 86.9% (mean gap 8.9 dB)[2011]. Both are good results; the lesson is that the value of the superstructure is the stable short bridge it normally permits, and that careful technique and tension can substitute for some of that advantage when the surgeon takes the trouble.

THow big and how durable is the effect?

These are not soft qualitative claims; the magnitude has been measured. In Yung and Vowler’s analysis of 242 ossiculoplasties for chronic otitis media, overall success — air-bone gap closed to within 20 dB — was 66.5% at six months and fell to 50.3% by five years. On multivariate analysis, which isolates each factor from the others, a present malleus made success 6.36 times more likely at six months. More strikingly, when the same cohort was re-examined at five years, a present malleus was the only factor that still independently predicted success, raising the odds 2.65-fold; an absent malleus was the single significant unfavourable factor for the long-term result[2006].

Two features of that finding deserve emphasis. The first is independence: the malleus effect survives adjustment for aeration, disease and the other prognostic variables, so it is not merely a marker of an otherwise healthier ear. The second is durability: where many favourable factors lose their statistical force over time as ears drift, the malleus remained the standout long-term predictor — a clue that its benefit is bound up with the stability of the reconstruction rather than only its initial acoustics. The stapes superstructure carries a similar, independent favourable weight in prognostic series and risk indices: studies using the Middle Ear Risk Index and multivariate models consistently place greater ossicular loss, including loss of the stapes superstructure, on the unfavourable side of the ledger[2009, 2001].

CMechanism versus stability: reconciling the evidence

A thoughtful clinician will notice an apparent paradox. If the malleus matters so much in clinical series, why do controlled temporal bone experiments show such a small effect? Shimizu and Goode reconstructed eight human temporal bones with and without the malleus and measured stapes footplate velocity by laser-Doppler vibrometry. Reconstruction without the malleus tended to be slightly worse between 0.6 and 3.0 kHz, but the difference did not reach statistical significance [2008]. Taken alone, that might suggest the malleus is acoustically almost irrelevant.

The resolution is that a temporal bone measures the wrong thing for this question. It captures the instantaneous transfer function of a freshly, perfectly assembled construct held motionless on a bench. It cannot capture what unfolds over months and years in a living ear: prosthesis migration, drum retraction, healing, scarring, fluctuating pressures and the slow loosening or tipping of a construct that lacks firm lateral support. The clinical advantage of the malleus is therefore best understood as primarily one of mechanical stability and durable coupling, not a large intrinsic acoustic gain — which is exactly why its benefit is modest in vitro yet powerful and, above all, long-lasting in patient series [2008, 2006]. The two literatures do not conflict; they describe different timescales, and together they sharpen the mechanism rather than muddy it.

The same reasoning explains the stapes superstructure. Bench measurements show that bypassing the superstructure with a well-seated TORP onto the footplate transmits sound nearly as well acutely; the clinical edge of the superstructure comes from the shorter, more stable, more forgiving construct it permits, which is what protects the result over time[2001]. In both cases the practical maxim is identical: the surviving structure buys you durability, and durability is what separates a good early audiogram from a good audiogram five years on.

CPutting it to work: counselling and planning

Three practical consequences follow directly. First, counsel from the anatomy. When the surgeon documents the malleus and stapes status at operation, the patient’s likely outcome can be discussed in concrete terms: a type A ear can be offered the best prognosis in ossiculoplasty, while a type D ear — no malleus, no superstructure — warrants frank, guarded expectations and a lower threshold for staging or for accepting a hearing aid. These two findings predict the result more reliably than the choice of titanium, hydroxyapatite or autograft.

Second, preserve the survivors. Because both structures are independent favourable factors, neither should be sacrificed casually. A healthy, mobile stapes arch must never be removed merely to drop in a total prosthesis, since that converts a favourable defect into a worse one; and a present malleus should be retained and engaged, lateralising it by dividing the tensor tympani tendon if it is medialised, rather than bypassing it. Equally, confirm that an apparently intact superstructure is genuinely mobile— a tympanosclerotic or otosclerotic fixation will defeat any reconstruction however perfect the bridge.

Third, let the anatomy, not the implant, lead the prognosis. The strongest, most reproducible message of the prognostic literature is that the surviving ossicular elements outweigh the prosthesis material in deciding the result [2001]. A present malleus and a present, mobile stapes superstructure are independent, measurable, durable advantages; respect them, retain them, build on them, and the reconstruction will reward the patient with hearing that lasts.