The AOFAS foot and ankle scores: what they measure and why the society withdrew them

Kitaoka and colleagues published four rating systems together in 1994, one for each region of the foot: the ankle and hindfoot, the midfoot, the hallux metatarsophalangeal and interphalangeal joints, and the lesser toes. Each totals 100 points and each is built from pain, function and alignment.

The ankle-hindfoot scale allocates 40 points to pain, 50 to function across seven items and 10 to alignment. The hallux and lesser toes scales allocate 40 to pain, 45 to function across six items and 15 to alignment. We publish the ankle-hindfoot, hallux and lesser toes scales; the midfoot scale is not yet published here because the sources we could reach disagreed on one of its point values, and we do not publish a scoring table we cannot confirm.

Every AOFAS scale combines what the patient reports with what the examiner measures. On the ankle-hindfoot scale, 40 of the 100 points come from the examiner — gait, sagittal motion, hindfoot motion, stability and alignment. On the hallux and lesser toes scales it is also 40 of 100: joint motion, stability, callus and alignment.

That means a total cannot be collected by post, by telephone or by an electronic form, and it cannot be read as a patient-reported outcome even though it is often presented as one. Reporting the pain, function and alignment components beside the total, rather than the total alone, restores some of what the single number conceals.

In 2011 the American Orthopaedic Foot and Ankle Society published a position statement withdrawing its endorsement of its own clinical rating systems. The grounds were that they were never formally validated and do not meet current standards for outcome measurement: the point weightings were assigned by expert consensus rather than derived from patient data, and the developers did not establish the scales’ reliability.

The withdrawal is a scientific statement, not a legal one. Nobody is prohibited from using the scales, and the published tables are reproduced freely. But a society telling its members that its own scale is not an adequate outcome measure is a stronger reason to avoid choosing it than any licensing consideration would be.

Check which of the four scales was used, because their points are distributed differently and totals are not comparable across them. Expect a ceiling effect: a painless, well-aligned, stable foot scores close to 100 even when joint motion is limited, because motion carries only a small fraction of the points.

No minimal clinically important difference has been established for any of the scales, so a change of a given number of points cannot be called meaningful. The grades of excellent, good, fair and poor at 90, 80 and 70 are a convention that grew up in the literature, not part of the original publication. On the ankle-hindfoot scale, the walking-distance item is expressed in city blocks of roughly 100 metres, which is interpreted inconsistently outside North America.

For a patient-reported outcome after foot and ankle surgery, the Foot and Ankle Ability Measure and the Foot and Ankle Outcome Score are both validated and both published on this site. For the forefoot, the Manchester–Oxford Foot Questionnaire was developed for foot and ankle surgery, and the PROMIS physical function measures are an option where a generic measure is wanted.

If the aim is to compare with an existing series that reported an AOFAS score, collect the AOFAS alongside a validated patient-reported measure, so the new data can be set against the old without being limited to it.