Hello, my name is Eli Schmidt. I am a medical student at the University of Iowa Carver College of Medicine, and I am presenting my project, Factors Influencing Different Classes in Progressive Collapsing Foot Deformity. Here are the relevant disclosures. So a recent consensus statement proposed a new nomenclature for what was previously called flat foot. It is now called progressive collapsing foot deformity, or PCFD. The same consensus statement also introduced a new classification system for the disease. This classification system includes two stages, flexible and rigid, and five classes, classes A through E. Each class also has its own associated radiographic findings. Although PCFD is understood as a complex and three-dimensional deformity, these classes are often treated as independent from each other. This begs the question, does the deformity defining each class have an impact on the deformities of other classes, and if so, to what extent? Our objective for this study is to assess the influence and impact of each PCFD class on the other classes by evaluating their associated angular measurements. We hypothesized that each class would be positively and linearly correlated with at least one other class, and that that influence would be high. 32 PCFD feet and 28 control feet were assessed using weight-bearing CT scans, and all measurements were completed by two foot and ankle surgeons. So again, according to the new classification system, each deformity is associated with specific measurements. In this study, every measurement was completed on each foot. The deformity and the radiographic measurements for each class are as follows. For class A, the deformity is hindfoot valgus, and this was measured using the hindfoot moment arm. And note, for each of these deformities, a conventional radiographic image is shown on the left to show the deformity, and a weight-bearing CT image is shown on the right as an example of the measurement that was completed. For class B, midfoot abduction was the deformity, and this was measured using the tail and navicular coverage angle. For class C, medial column instability was the deformity, and this was measured using the MIRI angle. Peri-Taylor subluxation for class D was measured using medial facet uncoverage, and class E, or ankle valgus, was measured using the Taylor tilt angle. We performed the relevant statistics, and each class was evaluated separately after removing confounding variables. For the results, in class A, MIRI was positively correlated with hindfoot moment arm, explaining 21% of the changes seen in that angle. For class B, medial facet uncoverage was correlated with the tail and navicular coverage angle, explaining 63% of the variation. For class C, both hindfoot moment arm and medial facet uncoverage were positively correlated with MIRI's angle. Together, these two measurements were responsible for 58% of the variation seen in MIRI's angle. For class D, tail and navicular coverage angle and MIRI correlated with medial facet uncoverage, and together were responsible for 63% of the variation seen in that angle. Finally, class E, being Taylor tilt angle a measure of ankle valgus, was not correlated with any other measurement. To conclude, this study demonstrated relationships between the classes of PCFD, the exception being that of ankle valgus in class E. We found a relationship between distinct features of PCFD that are commonly treated as independent from one another, further supporting the notion that PCFD is complex and three-dimensional. To go one step further, with each component impacting the others, it stands to reason that correction of a specific component may impact other aspects of a patient's overall deformity, and this would possibly decrease the necessity for additional procedures and would change how providers assess and surgically plan for PCFD. Thank you.

Progressive Collapsing Foot Deformity

classification system

angular measurements

correlations

interdependence