Abnormal Joint Moments in the Flatfoot during Walking

Abstract

INTRODUCTION: The flatfoot is characterized by collapsed medial arch of the foot during weight bearing, and the most common etiology is considered to be soft tissue dysfunction [1]. Analysis of biomechanical mechanism by muscles and ligaments is necessary for understanding the pathology in foot impairments [2]. Previously, differences of net moment in foot joints between the normal and flatfoot patients was investigated during walking using multi-segment foot model [3]. Although the net moment of a joint have provided clues on the forces and tensions of internal structures of the joint, separation of active moment by muscles and passive moments by connective tissues could help narrow the sources of joint problems [4]. Net moment can be easily obtained from even a stick model but the separation of active and passive moments requires a more sophisticated computational methods. Recently, a detailed musculoskeletal foot model has been developed to enable calculation of active moment by muscles and passive moment by ligaments [5]. The objective of this study was to calculate and compare the active and passive moments of the foot joints in normal and flatfoot separately for ankle, Chopart’s, Lisfranc and metatarsophalangeal joints during walking using a musculoskeletal simulation.

METHODS: This study was approved by Chung-Ang University IRB and a written informed consent was obtained from each subject prior to testing. Ten normal subjects (All males, 24.7±1.2 years, 173.4±5.6 cm, 71.1±9.1 kg) and ten subjects with flatfoot (All males, 23.5±2.3 years, 175.7±4.0 cm, 74.4±9.1 kg) were volunteered for the study. Flatfoot subjects were clinically determined by an orthopaedic surgeon based on physical examination. Full body motion during ground walking at self-selected walking speed was acquired using an optical motion capture system (6 cameras, Vicon, Oxford, UK), and ground reaction forces were measured using a force plate (OR6, AMTI, Boston, USA) and a pressure mat (FDM-S, Zebris, Isny im Allgäu, Germany). Plug-in-gait marker set for full body kinematics and Oxford foot marker set for foot kinematics were placed on each subject. Measured joint kinematics and external forces were input to the musculoskeletal foot model in AnyBody Modeling System (AnyBody Technology, Aalborg, Denmark). The musculoskeletal foot model was consist of five segments including toes, metatarsals, midfoot, talus and calcaneus with nine degree of freedom as shown in figure [5]. Active and passive moments for each instance during walking were estimated from tension of muscles and ligaments through inverse dynamics-based optimization in AnyBody Modeling System. The independent samples t-tests were used to quantify statistical differences between the normal and flatfoot groups with the significance level at 0.05 by using SPSS version 21 (SPSS Inc., Chicago, USA).

RESULTS: Maximum active, passive and net moments in direction of plantar flexion were calculated during the stance of walking for ankle, Chopart’s, Lisfranc and metatarsophalangeal joints as shown in the table 1. The net moment of flatfoot was significantly decreased 1.2, 1.4 and 0.4 %BW∙HT in the ankle, Chopart’s and Lisfranc joint, respectively. Statistically significant differences were also observed in the active and passive moments. The active moment of flatfoot patients was significantly decreased 1.2 %BW∙HT than that of normal foot in the ankle. While, the passive moment were significantly decreased only 1.6 %BW∙HT than that of normal foot in the Chopart’s joint.

DISCUSSION: Abnormal active, passive and net moments in the foot joints of flatfoot were shown for the individual joints by comparing them to the moments in normal subjects during ground walking. The significantly increased net moment of flatfoot subjects in the ankle joint conformed to previous studies [3,6]. The low magnitude of net moment is considered to be related to less efficient walking causing less functional walking.