SLR - December 2022 - Brandon Selby Blanken, DPM
Title: Unique Shape Variations of Hind and Midfoot Bones in Flatfoot Subjects—A Statistical Shape Modeling ApproachReference: Fallon Verbruggen F, Killen BA, Burssens A, Boey H, Vander Sloten J, Jonkers I. Unique shape variations of hind and midfoot bones in flatfoot subjects-A statistical shape modeling approach. Clin Anat. 2022 Nov 14. doi: 10.1002/ca.23969.
Level Of Evidence: IV
Reviewed by: Brandon Selby Blanken, DPM
Residency Program: Eastern Virginia Medical School - Suffolk Virginia
Podiatric Relevance: Most surgical decision-making has been dictated by two-dimensional (2D) radiological analysis. It can be difficult to evaluate the flatfoot condition on 2D radiographs, as the three-dimensional nature of the condition involves rotational aspects. Three-dimensional (3D) scanning is attractive for accurate treatment decision-making. Computer tomography (CT), has become more readily available. However, there is difficulty in extracting clinically relevant metrics from 3D surface reconstructions as clinicians try to apply previously learned 2D techniques Statistical shape models (SSMs) are a potential solution, as they provide relevant 3D metrics to showcase the natural shape variation of a given population. With guidelines of flatfoot diagnosis also relying on multiple criteria across the hind- and midfoot joints for condition classification the extension of such SSM analyses to multiple joints may reveal novel shape variations previously unreported, which may assist further flatfoot condition classification.
Methods: CT scans were obtained from 40 subjects (22 patients and 18 cadavers). Inclusion criteria for the scans were patients who had no history of degenerative or traumatic hind- or midfoot injury. Exclusion criteria were scans with incomplete imaging. The tibia, talus, calcaneus, navicular, and cuboid bones were then manually refined and smoothed. Segmentations were then exported as stereolithography (STL) files. Subjects were classified as either flatfoot or control based on the hindfoot alignment angle (HAA). A HAA greater than 7 lateral was considered flatfoot. The STL files were then processed to generate a SSM for the hindfoot joints. Shape variations were further processed to generate principle components (PCs) that were then compared between flatfoot and control groups.
Results: Of the patient cohort, 9 were classified as flatfoot deformity. Analysis demonstrated that flatfoot STJ’s had two significant PCs, in which flat feet correspond to a less pronounced, shortened calcaneus and talus along with a less thickened medial subtalar articulation of the calcaneus, and a more posteriorly oriented medial articulation slope, more adducted talar head, and more inferior inclined talar neck. For the TNJ, one significant PC demonstrated that flatfoot corresponds to a narrower, shallower navicular cup, more abducted talar body relative to the talar head, and a more prominent, posterior, and downward displaced medial tuberosity of the navicular. The CCJ presented trends of a more adducted calcaneus, more abducted cuboid, narrower calcaneal roof, and less prominent cuboid beak compared to control.
Conclusions: 3D generated standard shape models’ parameters were able to identify significantly different shape variations in the hindfoot between flatfoot and controls. Although the findings aren’t groundbreaking, the methodology in its own advances how flatfoot can be diagnosed and classified. As 3D imaging becomes more standard in a clinical setting, there will likely be a modernization in how it is diagnosed and classified. These advances may enhance understanding and computer-aided models of the intricacies of flatfoot, leading to better diagnosis and, ultimately, surgical treatment.