Diagnostic Accuracy of the Progressive Collapsing Foot Deformity (PCFD) Classification

Abstract

Background: A consensus group recently proposed the term progressive collapsing foot deformity (PCFD) and a new classification with 2 stages plus 5 classes to describe the complex array of flatfoot deformities. This study aimed to validate different diagnostic accuracy rates of the PCFD classification. Methods: This was a survey-based study distributed among 13 foot and ankle fellowship programs for 3 groups of participants with varied experience in practice (group 1: fellows in training, group 2: surgeons in practice for 1-4 years, and group 3: surgeons in practice for ≥5 years). Each participant was asked to assign 20 different cases of flatfoot deformity to the appropriate classes and stages using the PCFD classification. The overall diagnostic accuracy, class, and stage diagnostic accuracy rates for the 20 cases were calculated first for the entire cohort and then compared among the 3 groups. The misdiagnosis rate for each class of deformity (the sum of overdiagnosis and underdiagnosis rates) of the entire cohort was calculated and compared with the other classes. Mean and standard evidence were used to describe numerical data. One-way analysis of variance was used to compare values among the 3 groups and the 5 classes. P <.05 was considered statistically significant. Results: For the whole cohort, the overall diagnostic accuracy, class diagnostic accuracy, and stage diagnostic accuracy rates were 71.0%, 78.3%, and 81.7%, respectively There was a statistically significant difference between group 1 and 2, and group 1 and 3, in overall diagnostic accuracy and class diagnostic accuracy, with no significant difference among the 3 groups regarding stage diagnostic accuracy. Class B had a significantly higher overdiagnosis rate than the rest of the classes, whereas class D was significantly underdiagnosed than others. The misdiagnosis rates for classes A to E were 3.3%, 17.5%, 11.1%, 26.0%, and 3.7%, respectively. Conclusion: The PCFD classification showed overall fair diagnostic accuracy rates. The highest diagnostic accuracy was for “hindfoot valgus deformity” and “ankle instability.” Further content validation of the PCFD classification is needed to examine the terminology and interpretation of those classes with low diagnostic accuracy including “midfoot/forefoot abduction deformity,” “forefoot varus deformity/medial column instability,” and “peritalar subluxation/dislocation.” Level of Evidence: Level II, prospective comparative study.

Content validation of the progressive collapsing foot deformity classification

“…Among the total, 35.4% reported that "increased hindfoot moment arm" in class A was difficult to use (19.5% considered the description unclear, 11% did not how to diagnose it, 5% considered the term inaccurate, and 5% considered this concept was not suitable for clinical use), 42.7% reported that "increased foot and ankle offset" in class A was difficult to use (14.6% considered the description unclear, 13.4% did not know the term, 8.5% did not know how to diagnosis it, and 6.1% considered this concept was not suitable for clinical use) (Figure 6), 13.4% reported that the term "Sinus tarsi impingement" in class B was difficult to use (4.9% considered "sinus tarsi impingement" had an unclear description with a missing reference range for diagnosis, interest with precision and accuracy (15,16) . Lee et al (7) tested the reliability, Li et al (8) evaluated the diagnostic accuracy, while our study investigated the content validity of the PCFD classification.…”

“…The PCFD classification has been found to have moderate interobserver reliability, very good intraobserver agreement (7) , and good diagnostic accuracy (8) . The aim of this study is to validate the content accuracy of the PCFD classification system, an important step when a newly introduced classification system is being widely adopted for clinical use.…”

What’s New in Foot and Ankle Surgery

“…In an attempt to establish the diagnostic reliability of a new classification for progressive collapsing foot deformity, Li et al 16 distributed a survey to current trainees, graduates, and faculty of 13 foot and ankle fellowship programs. For the entire cohort, the diagnostic accuracy rates were 71.0% overall, 78.3% for class, and 81.7% for stage.…”

Influence of Weightbearing Computed Tomography in the Progressive Collapsing Foot Deformity Classification System

“…3 The reliability of this new system was assessed by Lee et al, 5 and found a multitude of possible combinations, a moderate interobserver reliability (0.56), a good intrarater reliability (0.85), and 1ABC (25.4%), 1AC (8.7%), and 1ABCD (6.9%) as the more prevalent subclassifications. Later, Li et al 6 tested the accuracy of surgeons with different experience levels in determining the correct classification and found a 71% to 81.7% rate.…”