Identification of the Apex of the Medial Longitudinal Arch Break in Progressive Collapsing Foot Disorder

Abstract

Category: Midfoot/Forefoot Introduction/Purpose: Progressive Collapsing Foot Disorder (PCFD) is caused by failure of both dynamic and static structures. The aim of this study was to identify the anatomical location of the medial longitudinal arch break in symptomatic flat foot deformity and analyze its relationship with Meary's angle. Methods: We analyzed weight-bearing radiographs of 81 patients [mean age 53.7 years (range, 18-81) with 101 flat feet. The apex of the medial arch break was determined on the lateral foot radiographs as the intersection of the anatomical axis of the talus and the first metatarsal. Therefore, the overall centre of rotation of angulation (CORA) of the medial arch break was documented as the angle at its apex (Meary's angle). Each separate joint angulation was then calculated to determine if the overall CORA was made of separate CORAs. Correlations between the apex location, and the number of apices, with Meary's angle were conducted. Results: There was an isolated apex of deformity in 50.4% (51/101) of cases. These were localised at talonavicular joint (TNJ) in 47% (24/51), the naviculocuneiform joint (NCJ) in 52.9% (27/51) and none at the cuneiform-first metatarsal joint (C-1MTJ). The remaining 49.5% (50/101) had combination apices with the primary deformity being at TNJ in 58% (29/50), the NCJ in 40% (20/50), and 2% (1/50) at the C-1MTJ. The mean Meary's angle was -17.9° for isolated and -18° for combination which was not statistically significant (p=0.92). There was no statistical difference in the talonavicular uncoverage angle between the single and combination apices group (p= 0.99). Conclusion: The apex of the medial arch break occurs distal to the talonavicular joint in the majority of cases, and thereby the main insertion points of the posterior tibial tendon and spring ligament. In 52.9% (27/51) of cases, the deformity occurs solely distal to the TNJ and in 58% (29/50) cases, it involves joints in addition to the TNJ. These will involve pathology of other structures, including the naviculocuneiform ligament. Surgical strategies in successfully correcting Progressive Collapsing Foot Disorder will therefore need to address joints distal to the TNJ in the majority of cases.