Peritalar Subluxation: A Key Finding for Both Cavovarus and Flatfoot Deformities
Authors: Li Shuyuan , Myerson Mark S. , Netto Cesar de Cesar 
Published: January 2022

Category: Hindfoot; Midfoot/Forefoot Introduction/Purpose: Peritalar subluxation in both the talonavicular and subtalar joints has been described as characteristic markers for adult acquired flatfoot deformity (AAFD). However, no study has reported these changes in in cavovarus deformity, and we postulated that peritalar subluxation would apply to both the AAFD as well as the cavovarus foot deformity but in different directions using the same markers. Furthermore, the use of calcaneocuboid (CC) joint subluxation as an additional marker for peritalar subluxation has never been investigated in either flatfoot or cavovarus deformities. This study used three dimensional images of weightbearing cone beam computed tomography (WBCT) to evaluate the alignment of the peritalar joints in feet with normal, varus and valgus hindfoot alignment. Methods: WBCT scan images and medical charts of 400 patients were retrospectively reviewed. Thirty cavovarus and 15 flexible AAFD feet were chosen as the study groups. Fifteen feet without deformities and arthritis, a history of trauma or surgery in both the hindfoot and ankle were chosen as controls. Hindfoot moment arm (HMA), Foot and ankle offset (FAO) were used to assess hindfoot alignment. Middle facet subluxation (MFS), talonavicular joint coverage angle (TNCA), and calcaneocuboid joint subluxation (CCS) were used as markers of peritalar subluxation. The talocalcaneal (Kite's) angle in the axial plane was used to demonstrate the relative position between the talus and the calcaneus. The arch height index in the sagittal plane was used to assess medial arch height. Positive was used to reflect lateral subluxations while negative for medial ones. Correlations between HMA, FAO and each of the above three peritalar subluxation parameters were assessed by bivariate linear regression. Results: Patients in both the cavovarus and the AAFD groups showed totally different hindfoot alignment, peritalar subluxation and the height of the medial arch compared to the control group. In the order of Cavovarus, AAFD, and Control, the mean HMA- CR values were -20.43mm, 14.02mm, and 0.03mm, respectively; HMA-WBCT values were -6.34mm, 15.75 mm, and 3.19 mm; FAO values were -11.17%, 7.42%, and 2.63%; TNCA were -16.8 degrees, 22.11, and 6.45; The MFS values were -17%, 42%, and 22%; CCS values were -21% (IQR=-35%,-0.17%), -7% (IQR=-11%, 0) and 0 (IQR=-4%, 5%); The Kite's angles were 22.19 degrees, 34.27 degrees, and 28.06 degrees; The arch height index values were 0.25, 0.71, and 0.44. There was a statistically significant difference among the three groups in all the above parameters. There was a strong positive linear correlation between each parameter of the peritalar subluxation marks with both hindfoot moment arm and FAO. Conclusion: This is the first study to bring the concept of peritalar subluxation to cavovarus deformity assessment, proving that peritalar subluxation is a key characteristic in both flatfoot and cavovarus foot deformities. The two deformities are pathologically completely different, and as expected, markers of peritalar subluxation were in opposite directions. The use of calcaneocuboid joint subluxation as additional marker of perisubtalar subluxation is novel to assess both deformities. The findings of this study will provide useful guidelines for future clinical evaluation and decision making in treating patients with either varus or valgus hindfoot deformities.