Dimensionality of Measures for Severe Unilateral Ankle Arthritis

ObjectiveTo analyze the dimensionality of 2 self-report outcome measures (Foot/Ankle Disability Index [FADI] and Short-Form [SF]-36), 3 biomechanical measures (stance and step symmetry measures, gait speed, and step width), 2 physical-performance measures (timed get-up and go [TUG] and 4-square step test [4SST]), and 1 clinician-report outcome measure (American Orthopaedic Foot and Ankle Society [AOFAS] Hindfoot Scale) in a patient population with unilateral ankle arthritis. These measures captured the following functions: mobility and speed, pain and its relationship to function, social integration, and symmetry and efficiency of gait.DesignCase series design.SettingBiomechanical research laboratory adjacent to a busy orthopedic clinical practice.PatientsSeventy-nine consecutive patients with unilateral traumatic arthritis who were candidates for a total ankle replacement.MethodsAn exploratory factor analysis with oblimin rotation was performed to determine the dimensions of the physical performance, biomechanical, self-report, and clinician-report measures.Main Outcome MeasurementsOutcomes measures included the SF-36 and pertinent subscales, gait speed, the 4SST, the TUG, the FADI, the AOFAS Hindfoot Scale, and biomechanical measures of step width, step symmetry, and stance symmetry.ResultsFour distinct dimensions were captured during factor analysis. Factor 1 included the TUG, gait speed, the 4SST, and step width; factor 2 included the FADI, the SF-36 bodily pain score, and the SF-36 physical function score; factor 3 included the biomechanical scores of stance symmetry ratio and the step symmetry ratio; and factor 4 included SF-36 social functioning and the AOFAS Hindfoot Scale.ConclusionsFindings suggest that various outcome measures for the ankle capture different dimensions and should be considered when evaluating the presence of disability or long-term change in outcome.