Flexible motion on articular surfaces in flatfoot during walking: Bi-planar Fluoroscopic Study

Abstract

INTRODUCTION: Collapse of the medial longitudinal arch in flatfoot patients is commonly caused by dysfunction of the tibialis posterior muscle during weight bearing conditions [1,2]. The collapsed arch results in a major dorsal subluxation of the talonavicular joint in the flatfoot. The severity of skeletal deformity in the flatfoot can be measured in radiographs at standing position. However, there is a lack of information on the joint kinematics of the flatfoot during daily activities. Previously, Levinger et al. quantified kinematics of the ankle joint complex in flatfoot subjects using the Oxford foot model with a skin marker-based motion capture system [3]. However, this method could not directly measure the talar motion because the talus is not palpable exteriorly. Recently, high speed bi-planar fluoroscopic systems have been used to measure foot kinematics noninvasively and accurately during walking [4]. The aim of this study was to quantify abnormal skeletal kinematics of the ankle joint complex and midtarsal joint in flatfoot during walking using a bi-planar fluoroscopic system.

METHODS: Eighteen normal and five flatfoot subjects volunteered in this study. The study was approved by the Institutional Review Board at Chung-Ang University. The flatfoot subjects were determined based on physical and radiographic examinations by an orthopaedic surgeon. Three-dimensional (3D) bone models of the foot were reconstructed from computed tomography images by using Seg3D software for each subject. A bi-planar fluoroscopic system was used to obtain the motion of the foot during the stance phase of walking [4]. Polygonal bone models of the tibia, talus, calcaneus, navicular and cuboid were registered to bi-planar X-ray images using a 2D-to-3D manual registration method. The articular contact surfaces in each bone were identified automatically using a template-based registration method [5]. Surface relative velocity vector (SRVV) has been proposed to quantify the magnitude and orientation of relative velocity vectors on articular surfaces [6]. We calculated SRVVs on the articular surfaces in the ankle joint complex (tibiotalar and subtalar joints) and midtarsal joint (talonavicular and calcaneocuboid joints) at every 10% during stance phase [6]. Average relative speed (ARS) and density map [7] was calculated for each joint based on the SRVVs on the articular surfaces (Fig. 1). The flatfoot kinematics during stance phase of walking was quantified and compared with normal foot kinematics using the independent samples t-tests at the significance level of p<0.05.

RESULTS: The SRVVs in the tibiotalar, subtalar and midtarsal joints in a representative frame are shown in Fig. 2. The polar density maps of SRVVs (Fig. 1) show modules and directional distribution of the velocity vectors on articular surfaces. During mid-stance, the SRVVs in the flatfoot were largely distributed in both radial and angular directions with peak density less than 0.02, while the SRVVs in the normal foot were concentrated and aligned with peak density larger than 0.03. In tibiotalar joint, the ARS was significantly larger in the flatfoot than normal foot from mid-stance to terminal stance (at 30, 50, 70 and 90% of stance phase) as shown in Fig. 3. The flatfoot subjects had larger ARS or relative motion during mid-stance in subtalar, talonavicular and calcaneocuboid joints than the normal subjects (p<0.05).

DISCUSSION: Our study suggested a method to quantify the joint motion based on the SRVVs on the articular surface. In the normal foot, the ankle joint complex and midtarsal joints performed large movement in early stance (0-10%) when the heel strike to the ground for shock absorption, and then the foot keeps stable during mid-stance (20-70%). However, the flatfoot subjects presented larger relative motion during mid-stance in ankle joint complex and midtarsal joint and even terminal stance in tibiotalar joint.