13The Ossiculoplasty Outcome Parameter Staging (OOPS) Index

FWhat the OOPS index is

Every ossiculoplasty ends with the same quiet question: how close to normal will this ear hear?The honest answer depends on far more than the prosthesis the surgeon chooses. It depends on the ear the prosthesis lands in — its ossicles, its mucosa, whether it is wet or dry, and how many times it has been operated on before. The Ossiculoplasty Outcome Parameter Staging (OOPS) index, published by John Dornhoffer and Elizabeth Gardner in 2001, is a simple tool that turns those features into a single number that predicts the postoperative air–bone gap (ABG)— the standard measure of conductive hearing result after reconstruction [2001].

The idea behind a staging index is borrowed from oncology: take the messy, individual reality of a case and place it on an ordered scale, so that prognosis, counselling and outcome reporting can all speak the same language. Earlier ossiculoplasty schemes — the Austin–Kartush ossicular grades, Bellucci’s otorrhoea classification, the Middle Ear Risk Index (MERI) and Black’s SPITE method — tried to do this by clinical intuition or by listing risk factors [1994, 1992, 1973]. What made OOPS different was its method: rather than guess which factors matter, Dornhoffer and Gardner let a statistical analysis of real outcomes tell them. The result is a compact, evidence-derived score running from 0 to 9, where a low number marks a favourable ear and a high number a difficult one.

FThe five variables and the score

OOPS is built from five intraoperative variables, each contributing a small number of points. The strength of the system is that every input is something the surgeon can read off directly at the microscope, and the weights reflect how strongly each factor moved the outcome in the derivation cohort [2001].

Add the points and the total falls between 0 and 9. A pristine, dry, primary ear with an intact chain scores 0; a multiply diseased ear — revision surgery, an absent malleus, active drainage, fibrotic mucosa and a canal-wall-down cavity — climbs toward the top of the range. The higher the score, the larger the air–bone gap you should expect to be left with. Build a score yourself below and watch the risk band move.

Two features of the weighting are worth noticing immediately. First, the ossicular variable is graded, not binary: a present malleus scores better (1) than an absent one (2), because the malleus handle gives a prosthesis a stable, well-vectored anchor. Second, the heaviest individual penalties — revision, fibrosis, a canal-wall-down cavity — describe the environment the reconstruction must survive in, not the choice of prosthesis. OOPS is, at heart, a way of scoring how hostile the ear is.

THow the index was derived

OOPS did not spring from opinion. Dornhoffer and Gardner reviewed 200 ossiculoplastiesperformed in 185 patients by a single surgeon, recorded a long list of candidate preoperative and intraoperative variables, and tested each against the measured postoperative air–bone gap using multivariate statistical analysis. Only the factors that remained independently associated with the outcome were kept; the rest were discarded. The five survivors became the index, and their relative weights were set to mirror their statistical influence [2001].

The single observation that anchors the whole system is the behaviour of the malleus. In the derivation cohort, ears in which the malleus handle was present achieved a markedly smaller mean postoperative gap than those in which it was absent — a difference large enough to reach statistical significance. By contrast, the choice between a partial (PORP) and a total (TORP) ossicular replacement prosthesis made essentially no difference to the mean gap. That pairing is why OOPS scores the malleus but does not score the prosthesis type at all [2001].

This is the deeper lesson of the OOPS derivation, and it generalises well beyond one index: a factor is only worth scoring if it survives multivariate scrutiny against the actual outcome. Surgical lore is full of variables that “obviously” matter but melt away once you control for everything else. OOPS earns its authority precisely because it threw such variables out.

TWhat OOPS leaves out, and why

The omissions are as instructive as the inclusions. Three variables that clinicians had long treated as central did notsurvive the analysis as independent predictors of air–bone-gap closure, and so they are absent from the score [2001]:

• The stapes superstructure.This is the most famous and most counter-intuitive of the OOPS findings. Generations of surgeons had taught that an intact stapes arch — allowing a PORP rather than a TORP — guaranteed a better result. In the OOPS cohort the presence of the superstructure was not an independent predictor of the gap once the other factors were accounted for, so it carries no points at all.
• Cholesteatoma. The specific disease label did not independently predict the outcome. What mattered was the statethe disease left the ear in — the mucosa, the drainage, the need for a canal-wall-down cavity — all of which OOPS already captures directly.
• The size of the preoperative air–bone gap. How bad the hearing was beforehand did not forecast how good it would be afterwards.

It would be a mistake to read these omissions as claims that the stapes arch or cholesteatoma are clinically irrelevant. The point is narrower and more rigorous: once you already know the surgery type, ossicular status, drainage, mucosa and mastoid anatomy, those additional labels add no extrapredictive power. A good index is parsimonious; it keeps only what pulls its weight. The disagreement with MERI — which does count the stapes — is a reminder that “obvious” prognostic factors do not always survive the statistics.

CDoes it actually predict? Validation

An index is only worth using if its number genuinely moves with the outcome. In the original series the correlation between the cumulative OOPS score and the postoperative gap was strong — a higher score reliably went with a larger gap [2001]. But a model built and tested on the same single-surgeon cohort always flatters itself; the real test is whether OOPS holds up in other hands.

It largely does. A study of 526 chronic-otitis-media ears treated with tympanoplasty scored every case with both OOPS and MERI and compared how well each discriminated the hearing outcome. OOPS came out ahead at both three and twelve months, with a receiver-operating-characteristic area of about 0.64 against roughly 0.5–0.55for MERI — the latter barely better than chance [2021]. The chart sets the two indices side by side.

Other work points the same way. Series correlating cumulative risk scores with the air–bone gap have repeatedly found that a rising score tracks a rising gap [2009], and the recent multi-institutional Ear Environment Risk study — the largest benchmark yet, with 1,679 ears — confirmed that OOPS outpredicts MERI, though it edged ahead of both with its own purpose-built scale [2025]. The consistent message is that OOPS is the better of the two classic indices, yet all of them correlate with outcome only modestly. The score and the result move together far more often than chance, but the score still leaves much of the variability in an individual ear unexplained.

CUsing OOPS in the clinic

How, then, should a thoughtful surgeon use OOPS? The honest state of the evidence — a clear front-runner that is still only modestly predictive — points to a few principles.

Use it for banded counselling, not decibel promises. The value of a modestly correlated score lies at the level of groups, not individuals. You cannot tell a patient their gap will be 19 dB, but you cantell the patient whose ear scores 7 that ears like theirs, on average, end up with a substantially larger gap than a favourable ear — and that staging the reconstruction or accepting more modest goals is reasonable. The score turns a vague sense that “this is a difficult ear” into a defensible, comparable statement [2001, 2021].

Let the malleus, not the prosthesis, drive your expectations.The derivation data are clear that a present, mobile malleus predicts a better result, while the PORP-versus-TORP decision does not move the mean gap. Preserve and use the malleus as a load-bearing strut wherever you can, and do not promise a better result simply because the stapes arch happens to be intact [2001].

Respect what the score cannot see.OOPS captures none of the microscopic intraoperative realities — fibrotic adhesions, the true mobility of the footplate, round-window patency, the quality of the malleus as an anchor — that often decide an individual case, and some of its inputs carry interobserver subjectivity. Use OOPS to structure honest, risk-banded counselling and to standardise outcome reporting between cases and centres. Do not use it to promise a decibel, to refuse an operation outright, or to replace the audiogram and your own eyes at the microscope. Within those limits, OOPS remains one of the few genuinely evidence-derived instruments the ossiculoplasty surgeon owns [2021, 2025].