From acquired flatfoot to progressive collapsing foot deformity: a review of classifications

Flatfoot deformity has historically been a complex problem, characterized by a combination of multiplanar deviations. To date, a wide range of classifications has been proposed, based on various principles—from posterior tibial tendon dysfunction, historically considered the primary cause of deformity, to segmentation by foot regions and specific types of deformities within them. A major challenge lies in the fact that foot deformity, as described below, does not follow a linear pattern, and various deformity combinations frequently occur, complicating its systematization. The work aimed to analyze existing and most widely used classifications of flatfoot deformity that have been proposed at different times and remain relevant in foot and ankle surgery, with emphasis on their features and limitations. A scientific data review was conducted using PubMed, eLIBRARY.RU, and CyberLeninka databases with the search terms классификация плосковальгусной деформации / classification of flatfoot deformity and flatfoot deformity. A total of 12 sources were selected for the review. The analyzed scientific data covered the period from 1988 to 2025. In the course of the review, an evident trend was identified toward more detailed segmentation of the deformity by different regions of the foot and the types of abnormalities within them. We observed a shift from hierarchical to faceted classifications, reflecting attempts to encompass the wide variability of deformities across all foot regions and their combinations encountered in clinical practice. And despite numerous attempts at systematization, there is still no universal classification that fully reflects all aspects of flatfoot deformity and satisfies the needs of clinicians in determining patient management strategies for this condition.