7Reconstruction on a Mobile Versus Fixed Footplate

FWhy the footplate decides the operation

When the surgeon opens an ear and finds the stapes superstructure gone— the capitulum and the two crural arches eroded away by years of chronic otitis media or cholesteatoma — the reconstruction is not yet decided. What remains is the footplate, the small oval plate of bone suspended in the oval window on its annular ligament, and the single most important question of the whole operation is whether that plate still moves. A prosthesis can only deliver sound to the cochlea if the structure it stands on can transmit that sound onward; a column resting on a plate that cannot piston is a column that carries nothing. Footplate mobility therefore divides the absent-superstructure ear into two completely different operations[1971].

If the footplate is mobile, the oval window is already doing its job: the missing element is only the bridgebetween the footplate and the drum. Rebuilding that bridge is a mechanical task — a total ossicular replacement prosthesis (TORP) spanning footplate to drum or malleus — and the vestibule is never opened. If the footplate is fixed, the problem is no longer a missing column but a blocked window: the plate itself will not move, and no bridge placed upon it will conduct until the window is re-opened by stapedotomyor, occasionally, mobilisation. The same anatomical defect — an absent superstructure — thus demands either a simple span or an entry into the inner ear, depending entirely on one property felt at the tip of a pick.

FReading footplate mobility at surgery

Because so much follows from it, the test for mobility must be done deliberately and gently. After the superstructure is confirmed absent and the oval niche is cleared of any obstructing scar, granulation or tympanosclerotic plaque, the surgeon places a fine pick or a small flat instrument on the footplate and applies the lightest pressure, watching for the plate to visibly piston in and out of the niche. A mobile footplate dips and recoils; a fixed one sits rigidly, often with white sclerotic plaque crusting its margin or bridging it to the niche wall.

Several cautions surround this simple manoeuvre:

• Be gentle. Heavy pressure on a thinned footplate can fracture it, creating a floating footplate— a fragment loose in the vestibule that is far harder to manage than either a mobile or a fixed plate.
• Clear the niche first. Adhesions, a fibrous band, or a plaque can splint a footplate that is actually mobile, giving a false impression of fixation; the niche must be inspected and freed before judging.
• Distinguish the level of fixation. A stiff chain can also reflect malleus head fixation in the attic; the footplate may be mobile while a more lateral block masquerades as oval-window fixation. Each ossicle is assessed in turn.

The reward for getting this right is large, because the two paths diverge so sharply: a misread mobile footplate leads to an unnecessary and risky entry into the vestibule, while a misread fixed footplate leads to a beautifully placed prosthesis that hears nothing.

TThe mobile footplate: span it with a TORP

When the footplate is mobile, reconstruction is conceptually straightforward and the vestibule stays closed. A TORP— in titanium, hydroxyapatite or a composite — is seated on the footplate and carried out to the reconstructed drum or, better, coupled toward the malleus handle. Where the lateral end lands matters: a malleus-to-footplate construct anchors the column to a firm, central point and recovers part of the native ossicular lever, transmitting several decibels more across the speech frequencies than a column running straight from the drum to the footplate [2005]. In a large prospective series of ears with an intact mobile footplate, a malleus-to-footplate TORP combined with malleus relocation and a stabilising technique produced a mean residual air–bone gap of just 8.9 dB, with closure to within 10 dB in roughly seven of ten ears [2011].

The recurring difficulty is not the column itself but its seat. Unlike the cup-shaped stapes head a partial prosthesis would rest in, the footplate is a smooth, flat, socketless plate: a foot balanced on it tends to tilt, rock and migrate as the ear heals, and a long strut magnifies any tilt so that force is delivered obliquely rather than axially into the cochlear fluids. The standard countermeasure is to manufacture the socket the footplate lacks — classically the cartilage “shoe”, a small oval cartilage plate roughly 2.5 × 3.5 mm with a central hole, set in the oval niche so that the hole grips and centres the prosthesis foot while still letting the footplate piston freely [2008]. The head is protected from the drum by a thin cartilage cap to resist extrusion, and the column is sized for the loosest length that remains positionally stable, since over-lengthening stiffens the annular ligament and can subluxate the footplate.

Crucially, stabilising the foot must never mean fixingit. The annular ligament supplies most of the chain’s compliance; a shoe that splints the footplate, or bone pate packed rigidly into the niche, would convert a mobility problem into a fixation one and undo the very reconstruction it was meant to support. The aim is a compliant centring cushion, not a rigid mounting.

TThe fixed footplate: open the window first

A fixed footplate changes the problem entirely. The most common cause in the chronic-ear population of this atlas is tympanosclerosis, in which calcified plaques stiffen the chain and crust the oval window niche, although congenital fixation and otosclerosis coexisting with chronic disease are also seen [2010]. Whatever the cause, a column placed on a rigid plate transmits nothing, so the window must be made to move again. Two strategies exist:

• Stapedotomy— a small calibrated fenestra is made in the footplate (or the plate is partially removed) and a piston is placed, restoring a controlled, mobile coupling into the vestibule. This is the more reliable approach and the one most analogous to otosclerosis surgery.
• Mobilisation— the fixed plate is gently freed from its sclerotic moorings without fenestration. It is simpler and avoids opening the vestibule, but is notorious for early refixation, so its results are less durable.

Opening a chronically diseased footplate has long been regarded as hazardous, because tympanosclerotic plaque can make the plate thick, brittle and adherent, raising the risk of fracture and of sensorineural injury. Yet careful series have shown the operation can be safe and effective when the rules are respected: in a review of 68 tympanosclerotic stapes fixations treated by stapedotomy, the air–bone gap closed to within 20 dB in 70% of ears (within 10 dB in 39%), bone conduction was unchanged in 92%, and no patient suffered a sensorineural loss [2002]. Where the malleus and incus are also involved, the window may be fenestrated and the chain rebuilt in the same sitting — a stapedectomy or stapedotomy combined with a cartilage-connected column to the oval window closed the gap to within 20 dB in six of seven such ears, best at the low and mid frequencies [2010].

The unifying principle is that with a fixed footplate the window itself is the lesion. Restoring its movement — not merely bridging to it — is the necessary first step, after which the lateral chain is reconstructed exactly as for any mobile footplate.

COutcomes across the footplate scenarios

Pooled across the literature, two patterns deserve emphasis at the clinic. First, the mobile-footplate TORP hears best when it recruits the malleus: malleus-to-footplate constructs give the narrowest residual gaps, and the device should default toward the handle whenever a usable one exists. Second, the fixed footplate is not a barrier to good hearing— stapedotomy in tympanosclerotic fixation closes the gap to within 20 dB in roughly seven of ten ears, comparable in magnitude to many ossiculoplasty series, provided the surgeon accepts the added vestibular risk and operates carefully [2002, 2010].

Set against this, it is worth remembering why the absent-superstructure ear, mobile footplate notwithstanding, tends to trail the ear with a present stapes head. A meta-analysis of 40 studies and more than 4,000 ears found partial prostheses seated on a present superstructure significantly more effective on average than footplate-seated total prostheses, with a combined risk ratio around 1.28 in their favour [2013]. Part of this is mechanical — the longer strut and the socketless plate — but part is selection: the very loss of the superstructure marks a more aggressive disease course, and an absent superstructure is an independent adverse prognostic factor in formal staging systems [2001]. The footplate-seated TORP is therefore the correct device for its indication, not an inferior one; its job is simply harder, and the company it keeps is sicker.

CDecisions, staging and pitfalls

The biomechanics and outcomes converge on a short clinical rule-set for the absent-superstructure ear:

Two judgements round out the picture. The first is staging. Entering the vestibule in an ear that is still inflamed, poorly aerated or freshly cleared of cholesteatoma compounds the sensorineural risk of stapedotomy with the uncertainty of an unstable bed. Many surgeons therefore stage the fixed-footplate ear: control the disease and re-establish a dry, aerated middle ear first, and open the window only once the ear is quiet. The second is honest counselling. A mobile-footplate reconstruction is a closed operation with a modest, predictable outlook; a fixed-footplate reconstruction involves opening the inner ear, with its small but genuine risk of sensorineural loss or vertigo, and the patient should understand which operation they are consenting to before the footplate is ever touched.

The single discipline that protects the patient through all of this is the one named at the start: palpate before you reconstruct. The footplate, not the absent superstructure, dictates whether the ear needs a simple span or an entry into the cochlea, and that one gentle test redirects the entire operation[1971, 2002].