Level V, expert opinion.

Recommendation: The historical nomenclature for the adult acquired flatfoot deformity (AAFD) is confusing, at times called posterior tibial tendon dysfunction (PTTD), the adult flexible flatfoot deformity, posterior tibial tendon rupture, peritalar instability and peritalar subluxation (PTS), and progressive talipes equinovalgus. Many but not all of these deformities are associated with a rupture of the posterior tibial tendon (PTT), and some of these are associated with deformities either primarily or secondarily in the midfoot or ankle. There is similar inconsistency with the use of classification schemata for these deformities, and from the first introduced by Johnson and Strom (1989), and then modified by Myerson (1997), there have been many attempts to provide a more comprehensive classification system. However, although these newer more complete classification systems have addressed some of the anatomic variations of deformities encountered, none of the above have ever been validated. The proposed system better incorporates the most recent data and understanding of the condition and better allows for standardization of reporting. In light of this information, the consensus group proposes the adoption of the nomenclature “Progressive Collapsing Foot Deformity” (PCFD) and a new classification system aiming at summarizing recent data published on the subject and to standardize data reporting regarding this complex 3-dimensional deformity. Level of Evidence: Level V, consensus, expert opinion. Consensus Statements Voted: CONSENSUS STATEMENT ONE: We will rename the condition to Progressive Collapsing Foot Deformity (PCFD), a complex 3-dimensional deformity with varying degrees of hindfoot valgus, forefoot abduction, and midfoot varus. Delegate vote: agree, 100% (9/9); disagree, 0%; abstain, 0%. (Unanimous, strongest consensus) CONSENSUS STATEMENT TWO: Our current classification systems are incomplete or outdated. Delegate vote: agree, 100% (9/9); disagree, 0%; abstain, 0%. (Unanimous, strongest consensus) CONSENSUS STATEMENT THREE: MRI findings should be part of a new classification system. Delegate vote: agree, 33% (3/9); disagree, 67% (6/9); abstain, 0%. (Weak negative consensus) CONSENSUS STATEMENT FOUR: Weightbearing CT (WBCT) findings should be part of a new classification system. Delegate vote: agree, 56% (5/9); disagree, 44% (4/9); abstain, 0%. (Weak consensus) CONSENSUS STATEMENT FIVE: A new classification system is proposed and should be used to stage the deformity clinically and to define treatment. Delegate vote: agree, 89% (8/9); abstain, 11% (1/9). (Strong consensus)

Background: Progressive peritalar subluxation (PTS) is part of adult acquired flatfoot deformity (AAFD). We investigated the use of the middle facet as an indicator of PTS using standing, weight-bearing computed tomography (CT) images. We hypothesized that weight-bearing CT would be an accurate method of measuring increased subluxation (“uncoverage”) and incongruence of the middle-facet among patients with AAFD. Methods: We included 30 patients with stage-II AAFD (20 female and 10 male; mean age, 57.4 years [range, 24 to 78 years]) and 30 matched controls (20 female and 10 male; mean age, 51.8 years [range, 19 to 81 years]) who underwent standing, weight-bearing CT. Two independent and blinded fellowship-trained foot and ankle surgeons measured the amount of subluxation (percentage of uncoverage) and the incongruence angle of the middle facet at the midpoint of its longitudinal length, using coronal-plane, weight-bearing, cone-beam CT images. Intraobserver and interobserver reliabilities were assessed using intraclass correlation coefficients (ICCs). Comparisons were performed using independent t tests or Wilcoxon tests. P values of <0.05 were considered significant. Results: Substantial to almost perfect intraobserver and interobserver reliability was observed for both measurements. We found that the middle facet demonstrated significantly increased PTS in patients with AAFD, with a mean value for joint uncoverage of 45.3% (95% confidence interval [CI], 38.5% to 52.1%) compared with 4.8% (95% CI, 3.2% to 6.4%) in controls (p < 0.0001). A significant difference was also found for the incongruence angle, with a mean value of 17.3° (95% CI, 14.7° to 19.9°) in the AAFD group and 0.3° (95% CI, 0.1° to 0.5°) in controls (p < 0.0001). A joint incongruence angle of >8.4° was found to be diagnostic for symptomatic stage-II AAFD. Conclusions: We investigated the use of the middle facet of the subtalar joint as a marker for PTS in patients with AAFD. We confirmed that standing, weight-bearing CT images allowed accurate measurements and that significant differences were found in the percentage of joint uncoverage and the incongruence angle compared with controls. Clinical Relevance: The assessment of the amount of subluxation and incongruence of the middle facet of the subtalar joint represents an accurate diagnostic tool for symptomatic adult acquired flatfoot deformity.

The 3D anatomical complexity of the foot and ankle and the importance of weight-bearing in diagnosis have required the combination of conventional radiographs and medical CT.Conventional plain radiographs (XR) have demonstrated substantial limitations such as perspective, rotational and fan distortion, as well as poor reproducibility of radiographic installations. Conventional CT produces high levels of radiation exposure and does not offer weight-bearing capabilities.The literature investigating biometrics based on 2D XR has inherent limitations due to the technology itself and thereby can focus only on whether measurements are reproducible, when the real question is whether the radiographs are.Low dose weight-bearing cone beam CT (WBCT) combines 3D and weight-bearing as well as ‘built in’ reliability validated through industry-standardized processes during production and clinical use (quality assurance testing).Research is accumulating to validate measurements based on traditional 2D techniques, and new 3D biometrics are being described and tested.Time- and cost-efficient use in medical imaging will require the use of automatic measurements. Merging WBCT and clinical data will offer new perspectives in terms of research with the help of modern data analysis techniques.Cite this article: EFORT Open Rev 2018;3 DOI: 10.1302/2058-5241.3.170066