Validity and internal consistency of the American Orthopaedic Foot and Ankle Society Midfoot Scale in patients with Lisfranc injury.

BACKGROUND

The American Orthopaedic Foot and Ankle Society (AOFAS) Midfoot Scale is an extensively used outcome measure instrument for evaluating outcomes after foot and ankle surgery or trauma.

METHODS

In total, 117 patients with Lisfranc injury completed the AOFAS Midfoot Scale and the Visual Analogue Scale Foot and Ankle (VAS-FA) instruments. Internal consistency (correlation between different items), floor and ceiling values, convergent validity, item threshold distribution, and the coverage (item difficulty) of the AOFAS Midfoot scale were tested.

RESULTS

AOFAS Midfoot Scale had high convergent validity and acceptable internal consistency (Cronbach's alpha >0.70). The ceiling effect was confirmed. The person-item distribution indicated that the scale had a lack of coverage and targeting in our sample.

CONCLUSIONS

Our data suggests that the AOFAS Midfoot Scale has acceptable validity and internal consistency. However, due to the lack of coverage and targeting, it should not be the primary outcome measure to be used to evaluate the outcomes after Lisfranc injury in the future studies.