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Foot and Ankle Outcome Score Validated for Adult Acquired Flatfoot Deformity

Sriniwasan B. Mani, BS
Hospital for Special Surgery

Haydee C. Brown, MD
Hospital for Special Surgery

Pallavi Nair, BS
Hospital for Special Surgery

Lan Chen, MD
Hospital for Special Surgery

Huang Do, MA
Hospital for Special Surgery

Stephen Lyman, PhD
Hospital for Special Surgery

Image - Photo of Jonathan T. Deland, MD
Jonathan T. Deland, MD
Attending Orthopaedic Surgeon, Hospital for Special Surgery
Image - Photo of Scott J. Ellis, MD
Scott J. Ellis, MD
Associate Attending, Orthopaedic Surgery, Hospital for Special Surgery
Associate Professor of Orthopaedic Surgery, Weill Cornell Medical College

When assessing a patient’s condition, doctors frequently use standardized performance tests and established sets of measurements that medical professionals across the field agree are accurate, reliable, and relevant.

These universally-recognized criteria aid in the initial diagnosis. They can also demonstrate the effectiveness of a treatment. By comparing the benchmark scores and results taken before treatment to the same tests taken during and after treatment, doctors can follow how and when a patient did – or did not – improve.

Having these agreed-upon, codified sets of data showing treatment outcomes also facilitates research. Outcomes from large groups of patients, taken over time and from different hospitals, can be accurately and reliably compared. Best practices are revealed, and the entire field benefits.

Without these sets of agreed-upon questions, accurate field-wide communication is not possible. Different tests can mean different things. Patient case histories cannot be accurately compared. Best outcomes cannot be determined.

That’s why an important area of medical research is validating whether a particular set of test scores or performance measurements can be reliably used to assess a patient’s condition. Validation allows all doctors across the field to speak the same language, using the same tests.

Now, an HSS-led study has validated the Foot and Ankle Outcome Score (FAOS) as being an appropriate and accurate test to use in assessment and treatment of a progressive condition known as Adult Acquired Flatfoot Deformity – or AAFD.

Measuring Patient Outcomes

The FAOS is a subjective survey of highly detailed questions covering a patient’s personal experience of important areas like pain, stiffness, quality of life, daily function, and recreational activities.

Each question has 5 incrementally rising answers from which patients choose the best description of their current condition. For example, when asked “Can you straighten your foot/ankle fully?,” the patient can select one of the five options of “Never, Rarely, Sometimes, Often, Always.”

The patient’s answers are computed into statistical analysis giving them a score indicating their degree of function. As treatment helps a patient’s condition improve, the answers can move up the scale, and as “Never” changes to “Always”, the scores improve.

HSS has used the FAOS, routinely over the past seven years, as the primary measurement when assessing the outcomes of patients treated for AAFD. Comparing patients pre-treatment scores to post-treatment answers allows consistent, measurable results that doctors can use to track individual patient’s outcome as well as compare treatment results for all patients.

The FAOS has also been previously validated to use when assessing two other conditions: lateral ankle instability and, more recently, for hallux valgus. However, until now, the FAOS had not been validated through specific, scientific assessment for AAFD.

Authenticating the Test Results

The research team was able to assess the validity of the FAOS by using a method of statistical analysis known a construct validity sample. Five areas – or domains as they are called in statistics – which correspond to sections of the FAOS, would be considered in the analysis to determine whether the questions in that area provided accurate, reliable measurement of patient function and experience. The domains were: 1) Quality of life, 2) Pain, 3) Daily Activities, 4) Mental Health, and 5) Sports/Recreation.

The collaborators reviewed 126 patients who had been diagnosed with flexible AAFD from 2006 to 2011 at HSS. During treatment, all the patients had been simultaneously assessed using two separate tests. One test was the FAOS. The second test was a widely used set of assessments known as the Short Form 36/Short Form 12 (SF-36/SF-12). 

Having two separate sets of evaluation scores for each patient, taken at the same time, allowed the research team to compare the two sets of test results to each other. What’s more, 49 of the patients completed answers to the FAOS not just once, but before and after treatment, adding to the research team’s ability to compare outcome results.

Further, 63 patients were asked to rate all the questions of the FAOS survey as whether or not the question was relevant to their AAFD condition. The patients assessed each question as being 1 (not relevant), 2 (somewhat relevant), or 3 (very relevant).  A score of 2 or more for a question would indicate the content of that question had acceptable validity and was appropriate to use when assessing AAFD.

Validity Demonstrated

The FAOS showed excellent construct validity. When comparing the results of the FAOS to the same time results of the SF-36 test of all 126 patients in the study, the FAOS showed strong correlation with the physical health component of the SF-36.

When comparing the scores of the 49 patients who had completed the FAOS before and after treatment, three domains – Quality of Life, Pain, and Daily Activities – were most responsive.

The patients who rated the relevance of the FAOS questions to their condition found Quality of Life and Sports/Recreation areas to be most relevant.

The study demonstrated that the FAOS can be utilized as a simple, effective tool for assessing patients with flexible AAFD. As the changing healthcare climate increasingly emphasizes patient-driven outcome measures, the validation of the FAOS gives doctors another valuable tool to help advance patient care.


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