12The Middle Ear Risk Index (MERI) Explained

FWhat MERI is and why it exists

Before any tympanoplasty or ossiculoplasty the surgeon is trying to answer a single hard question: how well is this particular ear likely to hear afterwards?The temptation is to look only at the ossicular chain — is the incus eroded, is the stapes intact? — but the surrounding middle-ear environment matters just as much. A draining, scarred, previously operated ear behaves very differently from a clean, dry, first-time ear, even when the ossicular defect looks identical. The Middle Ear Risk Index (MERI) was designed to capture that whole environment in one number [1994].

MERI grew out of Kartush’s 1994 work on ossicular reconstruction and was given its familiar modern form by Becvarovski and Kartush, who added smoking as a weighted variable. The idea is simple and powerful: take the disease- and surgery-related factors that experience says worsen outcome, assign each a numerical weight by severity, and sum them into a single 0–12 total. A low score describes a favourable ear; a high score flags a difficult one [1994, 2001]. That number lets you do three things you cannot do well by intuition alone: counsel the patient with honest, banded expectations; plan whether to reconstruct in one stage or two; and compare cases and outcomes consistently between surgeons and centres.

It is worth being clear about what MERI is not. It does not measure the preoperative audiogram, it does not specify a prosthesis length, and it does not assess cochlear reserve — that is the job of the bone-conduction thresholds. MERI is a prognostic risk score for the conductive, middle-ear side of the operation, and it earns its keep precisely because it forces attention onto the factors that surgeons most often under-weight.

FThe seven variables and their weights

The modern MERI sums seven weighted parameters. The exact point values differ slightly between published versions, but the structure and the relative weighting are consistent [2001]:

The weighting is the interesting part. Notice that ossicular status carries the widest range (0–4) and otorrhoeathe next (0–3), while perforation contributes least. That is deliberate: the surviving ossicular scaffold dominates both the surgical technique and the achievable result, and chronic drainage signals the inflamed, fibrosis-prone environment in which a prosthesis must survive. The chart makes the relative weights explicit.

Two of these variables borrow directly from older classifications. The otorrhoea grade is Bellucci’s four-step scale, which ties drainage to eustachian-tube and mucosal health [1973]. The ossicular grade follows the Austin–Kartushscheme, which categorises defects by the presence or absence of the malleus handle and the stapes arch — the two structures that most determine whether a reliable columella can be built [1971, 1994]. MERI is therefore not a rival to those systems but a way of combining them, with several other factors, into one comparable figure.

TScoring an ear in practice

Computing a MERI is quick once the ear has been examined and, ideally, the middle ear inspected at surgery. You grade each of the seven variables, add the points, and read off the band. The published thresholds put 0–3 in the mild band, 4–6 in the moderate band, and 7 or more in the severe, high-risk band [2001]. Build a few ears with the calculator below and watch how quickly several independently “minor” findings stack into a high total.

The single most important habit the calculator teaches is that MERI is additive. No one variable usually condemns an ear; rather, a wet history (1–2), some granulation (2), a revision setting (2) and a smoker (2) combine with even a modest ossicular defect to push the total well into the severe band before cholesteatoma is even considered. This is exactly why a clean-looking, dry-on-the-day ear can still be a high-risk ear. A second practical point: the otorrhoea variable describes the pattern of disease, not a single snapshot. An ear that is dry today but discharges every few weeks is graded as occasionally wet, not as dry.

Because some inputs — particularly the extent of granulation and the true ossicular status — are best judged under the microscope, MERI is often finalised intraoperatively rather than purely from the clinic examination. That makes it both a preoperative counselling tool and an operative record that travels with the case into any future revision.

TWhat the score predicts

The clinical value of MERI rests on a consistent finding across multiple series: higher scores track with poorer outcomes. As MERI rises, studies report a larger residual air–bone gap, lower rates of graft uptake, greater surgical complexity and more frequent revision and extrusion [2019, 2022]. A prospective tympanoplasty series of 200 ears, for instance, found that higher MERI correlated with a larger postoperative gap and a lower success rate [2019], and narrative reviews synthesising the wider literature reach the same conclusion [2022].

Within the index, the components do not all pull equally. Ossicular status remains the strongest single driver of hearing outcome: the presence of a usable malleus handle and a mobile stapes markedly improves the odds of closing the gap to within 20 dB [1994]. Chronic otorrhoea, cholesteatoma and granulationraise the score by marking an inflammatory ear that is prone to fibrosis, adhesion and prosthesis displacement. And the host- and history-related factors — smoking and previous surgery— raise it because they independently worsen graft survival and reconstruction stability; the smoking weight was added to MERI on exactly this evidence [2001].

The right way to use these predictions is by band, not by decibel. MERI cannot tell an individual patient they will end with a 17 dB gap. It can place their ear in a group whose average outcome is good, guarded or poor, and that is precisely the information an honest preoperative conversation needs. A severe-band ear is the one for which you discuss staging the reconstruction, temper the hearing target, and put amplification on the table from the outset.

CLimits, modifications and honest use

MERI is pragmatic and reproducible, but it is not a precise individual forecast, and a thoughtful surgeon should know its weaknesses. The score cannot see the microscopic intraoperative nuancesthat often decide a case — fibrotic adhesions, round-window obstruction, the true mobility of the footplate, the load-bearing quality of the malleus. Several of its inputs, notably the extent of granulation and the grading of fibrosis, carry real interobserver subjectivity, which limits how cleanly two surgeons will agree on the same ear [2022].

These limitations have driven modifications. The best known is the OOPS index of Dornhoffer and Gardner, built not from clinical intuition but from a multivariate analysis of 200 ossiculoplasties. Strikingly, in that derivation cholesteatoma and tympanic-membrane status did not independently predict the gap, so OOPS deliberately omits them and leans instead on mucosa, drainage, ossicular and malleus status, revision and surgery type [2001]. Black’s SPITEmethod — Surgical, Prosthetic, Infection, Tissue, Eustachian — took a complementary route, grouping twelve significant predictors into families designed more for structured counselling than for a single tidy number [1992]. The disagreement between these systems over which variables earn their place is a healthy reminder that an index is only as good as the cohort and the method that built it.

So how should MERI be used well? Score the whole ear, not just the chain— that is the entire point of the index, and the environmental variables it captures move the outcome at least as much as the ossicular defect. Read the result as a band to drive honest, comparable counselling and to decide on staging in high-risk ears. And respect what the score cannot see: use it to structure the conversation and to standardise comparison, never to promise a decibel, to refuse an operation outright, or to replace the audiogram and your own eyes at the microscope. Within those limits MERI remains one of the few genuinely useful, evidence-anchored instruments the ossiculoplasty surgeon owns [2022, 2019].