Evaluation for Postural Balance Pattern of Patients with Adolescent Idiopathic Scoliosis using Pressure Sensor Systems

Abnormal lateral curvature of the spine may affect postural balance pattern in static and dynamic condition. Previous studies demonstrated asymmetrical balance patterns of adolescent patients with idiopathic scoliosis during sitting and walking. However, pressure distribution data have been rarely used to analyze asymmetrical postural pattern of scoliotic patients. In this study, pressure data analysis for evaluation of postural balance in patients with idiopathic scoliosis was conducted by utilizing two types of pressure sensor systems. Subjects were classified into a control group, scoliosis with left convex side of the curve group, and scoliosis with right convex side of the curve group. All subjects were instructed to walk and sit on pressure sensor systems which is consist of a lot of capacitive sensors. Pressure distribution data were subdivided into two regions of masks and analyzed for maximum force, peak pressure, and contact area. There were significant differences in pressure distribution patterns between scoliosis patient groups according to the direction of the curve during walking and sitting. From these results, it was concluded that idiopathic scoliosis cause postural asymmetry and unequal weight distribution during walking and sitting. Furthermore, pressure sensor systems can be used to detect asymmetrical balance and postural change of patients with idiopathic scoliosis and provide accurate diagnosis and rehabilitation method for individuals. Introduction Postural balance is the ability to keep the line of gravity of a body within the base of support. The ability to keep balance is one of the most essential factors in activities of daily living. Human body tries to maintain its correct posture under static and dynamic conditions against gravity. Good posture provides normal biomechanical functions of the musculoskeletal system. However, improper postural alignment and trunk stability including asymmetrical pelvic tilt in the three different planes (frontal, sagittal, and transverse) and excessive curvature of the spine such as lordosis, kyphosis, and scoliosis can cause spinal deformities as well as influence on our balance system negatively. Previous studies discovered that abnormalities in balance function caused by progressive curve were found to be associated with pelvic deformities in the sagittal and frontal plane [1]. Scoliosis is a three-dimensional deformity defined as an abnormal lateral curvature of the spine. It is divided into two categories: congenital and idiopathic. Congenital is caused by vertebral anomalies Recent Advances on Mechanics, Materials, Mechanical Engineering and Chemical Engineering ISBN: 978-1-61804-295-8 138 present at birth and idiopathic means the identifying cause of the disease is unknown. Idiopathic scoliosis is defined by the age of onset such as infantile, juvenile, and adolescent. Generally, curve types of scoliosis are classified as C-shaped and S-shaped based on the direction and location of the curve in spinal deformity. C-shaped and S-shaped curves refer to a single and double curve, respectively, in the thoracic, lumbar, or thoracolumbar region. These curve types are connected to asymmetrical rotation, elevation, and tilting of the pelvis which can cause various pain-related symptoms. Adolescent idiopathic scoliosis (AIS) is the most common type that is present in 2 to 4 % of children between the ages of 11-17 years [2]. More severe curve that requires treatment is present more frequently in females than males. Initial asymmetry of the body during growth phases may affect progression of AIS. Progressive curve is related to posture asymmetry, and it can affect physical activity in adolescent. Scoliosis in adolescent has been closely associated with excessive spinal curvature, asymmetrical load on the spine, and progressive loss of both trunk and lower limb balance [3]. In biomechanics, the trunk and pelvis plays a fundamental role in the maintenance of body balance. Therefore, convexity and concavity of the spinal curve with pelvic inequality would alter the postural balance pattern in standing, sitting, and during walking. The scoliosis patients group displayed increasing displacement of the center of pressure (COP) and the center of mass (COM) excursion [4]. Aggravated scoliosis with pelvic imbalance leads to increasing several trunk muscle contraction, postural instability, and asymmetrical tilting angle while standing and sitting [5,6]. Shamberger [7] described the connection between asymmetrical alignment of the lower extremities and compensatory curvatures of the spine. Additionally, patients with idiopathic scoliosis showed asymmetrical gait in kinematic and ground reaction force (GRF) due to changes in postural control strategies [8]. To date, many studies related to postural balance of idiopathic scoliosis in adolescent have been conducted by utilizing various balance assessment systems. Muscle imbalance in the lumbar or thoracolumbar area on the convex side of patients with idiopathic scoliosis was observed by measuring electromyography (EMG) signals in thoracic, lumbar, and abdominal trunk muscles [9]. More reduced step length, pelvis, hip, and shoulder frontal motion, hip transversal motion, knee sagittal motion of scoliosis patients than normal subjects was observed by using three-dimensional motion analysis equipment [10]. However, pressure distribution data have been rarely used to analyze asymmetrical postural pattern of scoliotic patients in the literature. It is crucial to assess the pressure distribution pattern for patients with idiopathic scoliosis because pressure distribution data is useful to get the quantitative information about normal or abnormal balance pattern for individuals in static and dynamic conditions. In addition, in recent years, adolescent students spend most of time sitting with the increase in sedentary activities such as studying, watching television, and playing computer game. Bennett [11] reported that patients with AIS have muscular imbalance between concave and convex side of the spine as they spend most of time sitting. Accordingly, there is need to investigate the weight distribution pattern of AIS patients during sitting and effect of sitting balance control on body balance system during gait. Pressure sensors are commonly used in various medical fields to provide the information about postural balance of patients by converting electric signal into physical output. There are many pressure measurement methods including resistive, inductive, capacitive, and piezoelectric for measuring pressure between two contacting surfaces. Especially, capacitive sensors are more suitable than other sensors for assessing interface pressure due to its advantage of high sensitivity and linear characteristics. Platform system with capacitive sensors has been utilized to collect pressure distribution of the foot during walking [12]. In addition, capacitance mapping system was used to analyze the effect of the body asymmetry, trunk mobility, postural change caused by prolonged sitting in working conditions on spinal deformity [13]. The purpose of this study was to assess the postural balance pattern of AIS patients and to analyze the correlation between compensatory strategies of subjects during sitting and walking by utilizing two types of pressure sensor systems based on capacitive sensors. Recent Advances on Mechanics, Materials, Mechanical Engineering and Chemical Engineering ISBN: 978-1-61804-295-8 139 Methods Subjects Eighteen adolescents were recruited from the Department of Rehabilitation Medicine of Chungnam National University Hospital in Daejeon, South Korea. Subjects were consisted of three groups as shown in Fig. 1. The control group (CG) consisted of 6 adolescents without spinal deformation, previous history of injury, and abnormal gait pattern. The scoliosis patient group was divided into two subgroups according to the direction of the curve in scoliosis: scoliosis group 1 (SG 1) and scoliosis group (SG 2). The inclusion criteria for scoliosis patients were anteroposterior (AP) full spine standing X-ray evidence of idiopathic scoliosis with a C-shaped lumbar or thoracolumbar curve and no previous conservative or surgical treatment for the scoliosis. The SG 1 consisted of 6 adolescents with the left convex side of the curve and SG 2 consisted of 6 adolescents with the right convex side of the curve. Fig. 1. (a) Control group; (b) Scoliosis group 1; (c) Scoliosis group 2 All adolescents and their parents provided written informed consent prior to their voluntary participation. Characteristics of subjects about demographic data including mean age, height, body weight, body mass index (BMI), and Cobb angle are shown in Table 1. Table 1 Characteristics of subjects Control group (mean±SD) Scoliosis patients